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1 INFORMATION TO USERS This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted. The following explanation of techniques is provided to help you understand markings or notations which may appear on this reproduction. 1. The sign or target for pages apparently lacking from the document photographed is Missing Page(s). If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure you of complete continuity. 2. When an image on the film is obliterated with a round black mark it is an indication that the film inspector noticed either blurred copy because of movement during exposure, or duplicate copy. Unless we meant to delete copyrighted materials that should not have been filmed, you will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., is part of the material being photographed the photographer has followed a definite method in sectioning the material. It is customary to begin filming at the upper left hand comer of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again beginning below the first row and continuing on until complete. 4. For any illustrations that cannot be reproduced satisfactorily by xerography, photographic prints can be purchased at additional cost and tipped into your xerographic copy. Requests can be made to our Dissertations Customer Services Department. 5. Some pages in any document may have indistinct print. In all cases we have filmed the best available copy. International

2 LEE, JUNE BOK ELECTROCHEMICAL APPROACH TO THE CORROSION PROBLEMS OF SEVERAL IRDM-NICKEL-CHRQHIUM ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE WATER. THE OHIO STATE UNIVERSITY, PH.D., 1978 International 300 n. zleb road, anm arbor, mi asiob

3 ELECTROCHEMICAL APPROACH TO THE CORROSION PROBLEMS OF SEVERAL IRON-NICKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE WATER DISSERTATION P re s e n te d i n P a r t i a l F u lf il lm e n t o f th e R eq u irem en ts f o r th e D egree D octor o f P h ilo s o p h y i n th e G rad u ate School o f The Ohio S ta te U n iv e rsity By Ju n e Bok L ee, B.S., M.S. ****** The Ohio S ta t e U n iv e r s ity 1978 Reading Comm ittee: Dr. R. W. S ta e h le D r. G, R. S t. P i e r r e Dr. J. A. Begley ^ p r o v e d By ' d jà A d v ise r D epartm ent o f M e ta llu g ic a l E n g in e e rin g

4 IKNOWLEDGMENT The B ib le sa y s " A ll th in g s v/ere c r e a te d th ro u g h Him and f o r H im." (C o lo s s ia n s l : l 6 ). I w ish to e x p re s s my a p p r e c ia tio n to Dr. H.W. S ta e h le f o r h is a d v ic e, warmth and encouragem ent th ro u g h o u t th e c o u rs e o f t h i s s tu d y. S p e c ia l th a n k s to Dr. A.K, A graw al who p ro v id e d d ir e c tio n and g u id a n c e. I w ould l i k e to th a n k th e fo llow ing people fo r th e tim e, d iscu ssio n and unders ta n d in g th a t th e y have shown me d u rin g my te n u re i n : g ra d u a te s c h o o l, H. C hoi, H. Chaung, Ü. Kim, S. S z k la r s k a - Sm ialowska, F. Beck, J. Sykes, G. Welch, G. C ragnolino, W. N u tte r, P. C a r te r, H. S t.c l a i r e, B. F a r r a r, T. B ig g e r t, R. O tenberger. R. Ju stu s and M.S. Lee. I w ould a ls o l i k e to th a n k D rs. G. R, S t.p i e r r e and J.A. B egley who s e rv e d a s members o f re a d in g com m ittee f o r t h i s d i s s e r t a t i o n. F in a n c ia l s u p p o rt from th e E l e c t r i c Power R esea rc h I n s t i t u t e i s a ls o g r a t e f u l l y a p p r e c ia te d. F in a l ly, I w ould l i k e to e x p re s s my d e e p e st a p p r e c ia t i o n to my w ife Sung Hee, who h as shovm h e r lo v e i n e v e ry way; by bein g a good w ife and m other.

5 May 2, Born - S e o u l, K orea B.S., S eo u l N a tio n a l U n iv e r s ity, S e o u l, K orea M.S., The Ohio S t a t e U n iv e r s ity, Colum bus, Ohio P r e s e n t... R e searc h A s s i s t a n t, D epartm ent o f M e ta llu r g i c a l E n g in e e rin g, The Ohio S t a t e U n iv e r s ity, Columbus, Ohio FIELDS OF STUDY M ajor F ie l d : M e ta llu r g ic a l E n g in e e rin g * Aqueous C orro sion o f M etal * E le c tro c h e m is try * Therm odynam ics

6 TABLE OF CONTENTS Pages ACKNOWLEDGEMENTS... ü VITA... i i i LIST OF TABLES... v i i i LIST OF FIGURES... LIST OF SYMBOLS... v i i i i C h a p te r 1. INTRODUCTION THERMODYNAMICS OF IRON-NICKEL-CHROMIUM ALLOYS 2.1 I n tr o d u c tio n Thermodynamic d ata R e s u lts 8 3. CORROSION POTENTIAL OF IRON-NICKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE OXYGENATED WATER 3.1 I n t r o d u c t i o n T heory o f Oxygen E le c tro d e... 1? 3.3 E x p e rim e n ta l D e s c r ip tio n o f E x p e rim e n ta l System Specim en P r e p a r a t io n and M easurem ents R e fe re n c e E le c tro d e Oxygen A n a ly s is 3.4 R e s u lts D i s c u s s i o n C om parison o f E x p e rim e n ta l D ata w ith Thermodynamic E q u ilib riu m P o t e n t i a l s A M ath e m atical E x p re s s io n o f th e C o rro s io n P o t e n t i a l s o f I r o n - N ic k e l- Chromium A llo y s i n te rm s o f Oxygen Cone e n t r a ti o n s S i g n i f i c a n t O b s e rv a tio n s C om parison o f P r e s e n t S tudy ;v ith t h a t R e p o rte d i n L i t e r a t u r e 3.6 Summary o f E x p e rim e n ta l R e s u lts iv x v i

7 4. CORROSION POTENTIAL OF IRON-NICKEL-CHROMITJM ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE WATER; THE EFFECT OF HYDROGEN PEROXIDE Pages 4.1 I n tr o d u c tio n Theory o f Hydrogen P e r o x i d e E x p e rim e n ta l E xperim ental S etup and P rocedures Chemical'. A nalysis 4.4 R e s u lts D is c u s sio n C om parison o f P r e s e n t S tu d y w ith t h a t R ep o rte d i n L i t e r a t u r e CORROSION POTENTIAL OF IRON-NICKEL-CHROMIUM ALLOYS m HIGH TEI4PERATURE HIGH PRESSURE WATER; THE EFFECT OF HYDRAZINE 5.1 I n tr o d u c tio n Theory o f H y d r a z in e E x p e rim e n ta l E xperim ental S etup and P rocedures Chemical A n aly sis 5.4 R e s u l t s D is c u s sio n CORROSION POTENTIAL OF IRON-NICKEL-CHROMIUM ALLOYS IN WATER AT 250 C; THE EFFECT OF CHROMATE AND NITRATE 6.1 I n t r o d u c t i o n E x p e r im e n t a l R efreshed A utoclave System S ta tic A utoclave System Chemical A n aly sis

8 6.3 R e s u l t s Chromâte N i t r a t e 6.4 C o n c l u s i o n s...« ELECTROCHEMICAL KINETICS OF TYPE 304 STAINLESS STEEL IN HIGH TEMPERATURE OXYGENATED WATER 7.1 I n tr o d u c tio n E x p e rim e n ta l A nodic K in e tic s C ath o d ic K in e tic s 7.3 R e s u lts E f f e c t o f Scan R ate E f f e c t o f S u lf a t e C o n c e n tra tio n R everse Scan E f f e c t o f T em p eratu re E f f e c t o f Oxygen C urrent Decay Experim ent 7.4 D is c u s sio n E f f e c t o f S u lf a t e ; L i t e r a t u r e S urvey C a lc u la tio n s o f ph a t V ario u s Cone, o f S u lfa te a t Temp, between C E f f e c t o f S u lf a t e ; E x p e rim e n ta l T ra n s p a s s iv e Peak E s tim a tio n o f E le c tro c h e m ic a l P a ra m e te rs o f Oxygen R ed u c tio n K in e tic s H y p o th e tic a l P o l a r i z a t i o n Curve in Pure W ater a t 25O C Com parison o f P r e s e n t S tudy w ith th a t R ep o rted i n L i t e r a t u r e 7. 5.' Summary o f E x p e rim e n ta l R e s u l t s S u g g e s tio n s f o r F u tu re Work... I 60

9 8. LIST OF REFERENCES APPENDIXES APPENDIX A Thermodynamic C a l c u l a t i o n s Thermodynamic C a lc u la tio n s f o r th e C o n s tru c tio n o f P o te n tia l-p H D iagram s o f Iron-N ickel-c hrom ium A lloys in High Tem perature Aqueous S o lu tio n s o C a lc u la tio n o f E q u ilib riu m P o te n t ia l s as a F u n ctio n o f C o n c e n tra tio n o f D is so lv e d S p e c ie s in H igh T em p eratu re Aqueous S o lu tio n s o C a lc u la tio n - o f E q u ilib riu m Oxygen C o n c e n tra tio n o f Fe, Ni and Cr w ith t h e i r O xides in High T em perature Aqueous S o lu tio n s APPENDIX B M a te r ia ls o Nominal Com positions o T herm al H is to r ie s o M ic ro s tru c tu re s APPENDIX C F a c i l i t i e s APPENDIX D Raw D a t a o C o rro sio n P o t e n t i a l M easurem ents i n O xygenated High Tem perature Water o C orrosion P o te n tia l M easurements in High Temp. H igh P re s s u re W ater; The E f f e c t o f Hydrogen P e ro x id e 0 C orrosion P o te n tia l M easurements in High Temp, H igh P r e s s u re W ater; The E f f e c t o f H ydrazine 0 C orrosion P o te n tia l M easurements in High Temp. H igh P re s s u re W ater; The E f f e c t o f C hrom âte and N itr a te

10 LIST OF TABLES 1, Comparison o f E stim ated and E xperim ental V alues o f E n tro p ie s , The V alues o f A, B and M fo r Type 304, In c o n e l 600 and In c o lo y , T e s t M a trix f o r H ydrogen P e ro x id e S tudy , E f f e c t o f H ydrogen P e ro x id e on th e C o rro s io n and O xidation P o te n tia l in S im ulated BWR W ater a t , T e s t M a trix f o r H y d razin e S t u d y , T est M atrix fo r Chromâte and N itra te Study., 125 7, phrp f o r Sodium S u lf a t e S o lu tio n s ' 8, E le c tro c h e m ic a l P a ra m e te rs i n Oxygen R ed u c tio n K i n e t i c s , Thermodynamic D ata F ree E n e rg ie s o f F o rm atio n a t E le v a te d T e m p e r a tu r e s V alues o f H enry s Law C o n s ta n ts f o r Aqueous H ydrogen and O x y g e n O x id a tio n P o t e n t i a l s f o r V ario u s E k e c tro d e R e a c tio n s ( i n V o lts ) N e u tra l ph a t H igh T e m p eratu re A G (c a l/m o l) f o r th e r e a c t i o n s E q u ilib riu m P a r t i a l P r e s s u r e o f Oxygen E q u ilib riu m D is s o lv e d Oxygen C o n c e n tra tio n (mol/kg.hgo) E q u ilib riu m D is so lv e d Oxygen C o n c e n tra tio n (PPb)

11 LIST OF FIGURES F ig u re Page U P o te n tia l- p H Diagram o f Fe-Ni-Cr-HgO a t 100 C P o te n tia l- p H Diagram o f Fe-Ni-Cr-H^O a t 1$0 C P o te n tia l- p H Diagram of Fe-Ni-Cr-HgO a t 200 C P o te n tia l- p H Diagram o f Fe-Ni-Cr-H^O a t 250 C P o te n tia l- p H Diagram o f Fe-Ni-Cr-H^O a t 288 C E x p e rim e n ta l S etu p f o r O x y g e n W orking E le c tro d e A ssem bly C o rro s io n P o t e n t i a l s o f Type 304 v e rs u s Time; E f f e c t o f E le c tro d e C o n fig u ra tio n s C o rro s io n P o t e n t i a l s o f Type 304 v e rs u s Time; E f f e c t o f E le c tro d e C o n f ig u r a tio n s C o rro s io n P o t e n t i a l s v e rs u s Time a t 288 C C o rro s io n P o t e n t i a l s v e rs u s Time a t 250 C C o rro s io n P o t e n t i a l s o f P t v e rs u s D is so lv e d Oxygen C o rro s io n P o t e n t i a l s o f H i v e r s u s D is so lv e d Oxygen C o rro s io n P o t e n t i a l s o f Cr v e rs u s D is so lv e d Oxygen C o rro s io n P o t e n t i a l s o f Type 304 v e rs u s D is so lv e d O x y g e n C o rro s io n P o t e n t i a l s o f I n c o n e l 600 v e rs u s D is so lv e d Oxygen C o rro s io n P o t e n t i a l s o f In c o lo y 800 v e rs u s D is so lv e d O x y g e n C orrosion P o te n tia ls v ersu s D issolv ed Oxygen a t 250 C... 49

12 Figure 19, The E f f e c t o f T e m p eratu re Change on th e C o rro s io n P o t e n t i a l s i n D e a e ra te d W ater.. 2 0, The E f f e c t o f T e m p eratu re Change on th e C o rro s io n P o t e n t i a l s i n O xygenated W ater., 2 1, The E f f e c t o f Oxygen C o n c e n tra tio n Change on th e C o rro s io n P o t e n t i a l s a t 150 C , The E f f e c t o f Oxygen C o n c e n tra tio n Change on th e C o rro s io n P o t e n t i a l s a t 250 C 23o E q u ilib riu m P o t e n t i a l s o f Oxygen E le c tro d e E q u ilib riu m P o t e n t i a l s o f H ydrogen E le c tro d e E q u ilib riu m C o n c e n tra tio n s o f Oxygen v e rs u s Tem perature fo r th e O xid ation o f Fe, Ni and Cr C o rro s io n P o t e n t i a l s v e r s u s D is so lv e d Oxygen a t 250 C; The E ffe c t o f Oxygen Consumption i n th e System C o rro s io n P o t e n t i a l s v e r s u s D is so lv e d Oxygen a t 288 C; The E ffe c t o f Oxygen Consumption i n th e System C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d Oxygen C o n c e n tra tio n E f f e c t o f D is so lv e d Oxygen C o n c e n tra tio n on th e C o rro s io n P o t e n t i a l o f Type 304 S ta i n le s s S te e l a t 274 C,,,,, S chem atic D iagram o f Ag/AgCl R e fe re n c e E l e c t r o d e Ag/AgCl R e fe re n c e E le c tro d e C a lc u la te d and E x p e rim e n ta l S ta n d a rd E le c tro d e P o t e n t i a l s o f Ag/AgCl E le c tro d e w. r. t. S ta n d a rd H ydrogen E le c tro d e a t E le v a te d T e m p e r a tu r e.,,,..,, E le c tro d e P o t e n t i a l o f Ag/AgCl R e fe re n c e E l e c t r o d e...» E xperim ental Setup fo r Hydrogen P ero xid e, N i t r a t e and Chrom âte E q u ilib riu m P o t e n t i a l s o f H ydrogen P e ro x id e O x id a tio n R e a c tio n

13 F ig u re E q u ilib riu m P o t e n t i a l s o f H ydrogen P e ro x id e S e d u c tio n R e a c tio n... C o rro s io n P o t e n t i a l s v e rs u s Time a t 250 C, C o rro s io n P o t e n t i a l s v e rs u s Time a t 200 C, C o rro s io n P o t e n t i a l s o f Type 304 S ta i n le s s S te e l v e rs u s I n l e t H ydrogen P e ro x id e..... C o rro s io n P o t e n t i a l s o f In c o n e l 600 v e rs u s I n l e t H ydrogen P e ro x id e... C o rro s io n P o t e n t i a l s o f In c o lo y 800 v e rs u s I n l e t H ydrogen P e r o x i d e... C o rro s io n P o t e n t i a l s o f P la tin u m v e rs u s I n l e t Hydrogen P e ro x id e... C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d H ydrogen P e ro x id e a t 100 C C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d H ydrogen P e ro x id e a t 288 C C o rro s io n P o t e n t i a l s v e r s u s D is so lv e d Oxygen a t 288 C E f f e c t o f H ydrogen P e ro x id e on C o rro sio n and O x id a tio n P o t e n t i a l o f Type 304 S ta in l e s s S te e l and P la tin u m i n A e ra te d W ater 47. C o rro s io n P o t e n t i a l v e r s u s I n l e t Oxygen L e v el f o r 304 S ta i n le s s S te e l a t 250 C. 48. C o rro s io n P o t e n t i a l v e rs u s I n l e t Oxygen L e v el f o r In c o n e l 600 a t 250 C E q u ilib riu m P o t e n t i a l s o f H y d razin e O x id a tio n R e a c t i o n E q u ilib riu m P o t e n t i a l s o f H y d razin e R ed u c tio n R e a c tio n E x p e rim e n ta l S etu p f o r H y d razin e C orrosion P o te n tia ls v ersu s Time a t 100 C C o rro s io n P o t e n t i a l s o f Type 304 S ta i n le s s S te e l v e rs u s D is so lv e d H y d razin e.... Page

14 Figure Page 5if, C o rro s io n P o t e n t i a l s o f In c o n e l 600 v e rs u s D is so lv e d H y d r a z in e...» C o rro s io n P o t e n t i a l s o f In c o lo y 800 v e rs u s D isso lv ed H ydrazine C o rro s io n P o t e n t i a l s o f N ic k e l v e rs u s D is so lv e d H y d razin e...»... H I 5 7. C o rro s io n P o t e n t i a l s o f P la tin u m v e rs u s D is so lv e d H y d razin e C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d H ydrazine a t 200 C C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d H y d razin e a t 288 C,,, C orrosion P o te n tia ls v ersu s Time in Chroma.te S o lu tio n C orrosion P o te n tia ls v ersu s D issolved Chromât e a t 250 C... 12? 62. C orrosion P o te n tia ls v ersu s Time in C hrom âte S o l u t i o n C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d Chromâte a t 250 C C orrosion P o te n tia ls v ersu s Time in N i t r a t e S o lu tio n.,,, C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d N itra te a t 250 C C o rro s io n P o t e n t i a l s v e rs u s Time i n N i t r a t e S o l u t i o n C o rro s io n P o t e n t i a l s v e rs u s D is so lv e d N i t r a t e a t 250 C,, E le c tro d e A rrangem ent f o r P o la r i z a t io n S t u d y E f f e c t o f Scan R ate on th e P o la r i z a t io n C urve o f Type 304 S t a i n l e s s S te e l a t Room T em p eratu re,,, xii

15 Figure Page 70. E f f e c t o f Scan H ate on th e P o la r i z a t io n Curve o f Type 304 S t a i n l e s s S te e l i n 0.1 N Sodium S u lf a t e a t 250 C E f f e c t o f S can R ate on th e P o la r i z a t io n Curve o f Type 504 S t a i n l e s s S te e l i n IN Sodium S u lf a t e a t 250 C... I E f f e c t o f S can R ate on P o l a r i z a t i o n B eh a v io r l E f f e c t o f S u lf a t e C o n c e n tra tio n on th e A nodic P o l a r i z a t i o n Curve o f Type 304 S t a i n l e s s S te e l a t 250 C... l E f f e c t o f S u lf a t e C o n c e n tra tio n on th e C ath o d ic P o la r i z a t io n Curve o f Type 304 S t a i n l e s s S te e l a t Room T e m p eratu re E f f e c t o f S u lf a t e C o n c e n tra tio n on th e C ath o d ic P o la r i z a t io n Curve o f Type 304 S t a i n l e s s S te e l a t 250 C E f f e c t o f R ev e rse Scan on A nodic P o la r i z a t io n Curve o f Type 304 S t a i n l e s s s t e e l i n N Sodium S u lf a t e a t 250 C E f f e c t o f R ev e rse Scan on C ath o d ic P o l a r i z a t i o n Curve o f Type 304 S ta i n le s s S te e l in 0. IN Sodium S u lf a t e a t 250 C E f f e c t o f T e m p eratu re on Anodic P o la r i z a t io n Curve o f Type 304 S t a i n l e s s S te e l i n 0, IN Sodium S u l f a t e E f f e c t o f T em p eratu re on C ath o d ic P o la r i z a t io n Curve o f Type 304 S t a i n l e s s S te e l in 0. IN Sodium S u lf a t e E f f e c t o f Oxygen on P o l a r i z a t i o n Curve o f Type 304 S t a i n l e s s S te e l i n 0. 0 IN Sodium S u lf a t e a t 250 C C ath o d ic and A nodic P o l a r i z a t i o n Curve o f Type 304 S t a i n l e s s S te e l i n O xygenated 0.01N Sodium S u lf a t e S o lu tio n a t 250 C

16 Figure Page 82. C ath o d ic and A nodic P o l a r i z a t i o n C urves o f Type 3 0 k S t a i n l e s s S te e l i n O xygenated 0. IN Sodium S u lf a t e S o lu tio n a t 250 C C ath o d ic and A nodic P o la r i z a t io n C urves o f Type 30if S t a i n l e s s S te e l i n O xygenated 0. IN Sodium S u lf a t e S o lu tio n a t 200 C C a th o d ic an d A nodic P o l a r i z a t i o n C urves o f Type 304 S ta in le s s S te e l in Oxygenated 0. IN Sodium S u lf a t e S o lu tio n a t 150 C C a th o d ic and A nodic P o l a r i z a t i o n C urves o f Type 304 S t a i n l e s s S te e l i n O xygenated 0. IN Sodium S u lf a t e S o lu tio n a t 100 C C u rre n t Decay B e h a v io r o f Type 304 S t a i n l e s s S te e l i n 0. IN Sodium S u lf a t e S o lu tio n a t 250C C u rrent Decay B ehavior o f Type 304 S ta in le s s S te e l in 0.01N Sodium S u lfa te S o lu tio n s t 250C P o te n tia l-p H D iagram a t 200 C and U n it A c ti v ity o f D is so lv e d S u lp h u r S p e c ie s P o te n tia l-p H D iagram a t 300 C and U n it A c ti v ity o f D is so lv e d S u lp h u r S p e c i e s E f f e c t o f Sodium S u lf a t e on th e ph o f W ater a t 275 C P o te n tia l-p H Diagram fo r Fe-HpO-S System a t 200 C P o te n tia l-p H Diagram fo r Fe-HpO-S System a t 300 C C o n c e n tra tio n P r o f i l e s o f Oxygen and S u lf u r i n O xide F ilm o f Type 304 S t a i n l e s s S te e l, S u rfa c e C om p o sitio n o f Type 304 S ta i n le s s S te e l w ith A E S C ath o d ic and A nodic P o la r i z a t io n C urves o f Type 304 S ta in le s s S te e l in Oxygenated W ater a t 250 C... 19,2 96. E ffe c t o f Sodium S u lfa te on th e ph of W ater a t T e m p eratu res b etw een 100C and 288 C xiv

17 Figure page 97. lo g i ^ v s, 1/T P o la r i z a t io n C urves o f Type 304 S ta i n le s s S te e l i n O xygenated 0. IN Sodium S u lf a te a t 250 C A nodic P o l a r i z a t i o n C urves o f Type 304 S t a i n l e s s S te e l i n O.OIN Sodium S u lf a te S o lu tio n a t , Anodic P o la r i z a t io n C urves o f F e-n i-c r A llo y s i n O.OIN Sodium S u lf a t e S o lu tio n a t 288 C , S u rfa c e M orphology o f Type 304 S ta i n le s s S te e l a f te r th e C urrent Decay Experim ent in 0. IN Sodium S u lf a t e a t 250 C , S u rfa c e M orphology o f Type 304 S t a i n l e s s S te e l a f t e r th e C u rre n t Decay E xperim ent i n O.OIN Sodium S u lf a t e a t 250 C , S u rfa c e M orphology o f Type 304 S ta i n le s s S te e l a f t e r 200 h o u rs e x p o su re i n P ure W ater w ith 8 ppm O x y g e n , C o n c e n tra tio n P r o f i l e o f Ni i n Oxide F ilm o f Type 304 S ta i n le s s S te e l. ', , E f f e c t o f S u lf a t e on th e C o rro s io n P o t e n t i a l o f Type 304 S t a i n l e s s S te e l a t 250 C , M ic r o s tr u c tu r e s o f C r, N i, Type 304, In c o lo y 800 and In c o n e l F a c i l i t i e s l l i f C o rro s io n P o t e n t i a l v e rs u s Time in O xygenated W a t e r , C orrosion P o te n tia l versu s Time; The E f f e c t o f H ydrogen P e r o x i d e O * C orrosion P o te n tia l versu s Time; The E f f e c t o f H y d razin e C orrosion P o te n tia l v ersu s Time; The E f f e c t o f Chrom âte C orrosion P o te n tia l versu s Time; The E ffe c t o f N i t r a t e

18 LIST OF SYMBOLS a : ; A c ti v ity oc : T r a n s f e r c o e f f i c i e n t c : C o n c e n tra tio n Cpr. H eat C a p a c ity D : D if f u s iv it y E^: E le c tro d e p o t e n t i a l a t te m p e ra tu re T E^: : S ta n d a rd e le c tr o d e p o t e n t i a l a t te m p e ra tu re T F : F a r a d a y 's c o n s ta n t G^: S tan dard fre e energy o f form ation a t tem p erature T G : S tan d ard fre e energy o f form ation a t 25 C G^: A c tiv a tio n en e rg y o f c a th o d ic r e a c t i o n G^: A c tiv a tio n en e rg y o f d if f u s io n H^: H eat o f form ation i g : C ath o d ic c u r r e n t d e n s ity K : R e a c tio n c o n s t, o f a c t i v a t i o n c o n t r o lle d r a t e eq. H j: H e n ry 's law c o n s ta n t o f s p e c ie j m j: Aqueous c o n c e n tr a tio n o f s p e c ie j n : No. o f e le c tr o n s in v o lv e d in o v e r a l l e le c tro c h e m ic a l r e a c tio n P : P re s s u re P j: P a r t i a l p r e s s u r e o f s p e c ie j R : Gas c o n s ta n t S ; E n tro p y o f fo rm a tio n T : Tem perature ( K )

19 t : Tem perature ( C) V : V o lts X, y : R e a c tio n o rd e r z. : No. o f e le c tr o n s in v o lv e d i n r a t e d e te rm in in g s te p o f th e e le c tro c h e m ic a l r e a c t i o n S : ' D iffu s io n la y e r

20 1, INTRODUCTION S in c e l a t e I9 6 0 s i t h a s been r e a l i z e d t h a t th e a p p l ic a t io n o f e le c tro c h e m ic a l te c h n iq u e i s one o f th e m ost p r o d u c tiv e way o f a t ta c k i n g h ig h te m p e ra tu re h ig h p r e s s u r e c o r r o s io n p ro b le m s. I n d u s t r i a l l y, h ig h te m p e ra tu re h ig h p r e s s u r e e le c tr o c h e m ic a l s tu d ie s a r e p a r t i c u l a r l y u s e f u l i n th e fo llovd.ng a r e a s P ) : n u c le a r pow er, g e o th erm al a p p l i c a t i o n s, c r y s t a l g ro w th, f o s s i l pow er, d e s a l in a t io n, f u e l c e l l s, deep s e a te c h n o lo g y, deep o i l w e ll d r i l l i n g, s c a le d e p o s itio n and c o r r o s io n, - In h ig h te m p e ra tu re h ig h p r e s s u r e w a te r p a r t i c u l a r l y i n w a te r c o o le d n u c le a r r e a c t o r p la n ts th e F e-n i-c r a llo y s a r e b e in g u s e d e x te n s iv e ly, due to t h e i r e x c e lle n t c o rro s io n r e s i s t a n t p ro p e rty ^ ^ ^ In s p i t e o f t h e i r v e ry low g e n e ra l c o r r o s io n r a t e i n h ig h te m p e ra tu re h ig h p r e s s u r e w a te r ( < 1,2 5 u / y r, ) some u n e x p e c te d lo c a l i z e d c o r r o s io n problem s have d ev e lo p e d v jith th e u se o f th e s e a l l o y s. One o f th e s e lo c a l i z e d c o r r o s io n problem s i n n u c le a r pov/er p la n t i s s t r e s s c o r r o s io n c ra c k in g o f a u s t e n i t i c s t a i n l e s s s t e e l s - in h ig h te m p e ra tu re o x id iz in g e n v iro n m e n ts. The fo llo v o.n g s a r e th e th r e e g e n e ra l a r e a s ^ ^ ) : 1) s o lu tio n a n n e a le d f u e l c la d d in g i n a b o il in g w a te r r e a c t o r, 2) s e n s i t i z e d p ip in g and specim ens i n b o il in g w a te r r e a c t o r s and la b o r a to r y t e s t s i n o x y g e n a te d v ;a te r, r e s p e c t i v e l y, 3) s o lu tio n a n n e a le d o r s e n s i t i z e d specim ens i n la b o r a to r y t e s t s va.th doub^ë- Ü- bends o r slow s tr a in in g d ev ice in oxygenated w ater. 1

21 T h is r e s e a r c h work i s a p a r t o f a r e s e a r c h p r o je c t in v e s t i g a t i n g th e s t r e s s c o r r o s io n c ra c k in g o f F e-n i-c r a l lo y s i n r e a c t o r e n v iro n m e n ts, s p o n so re d by th e E l e c t r i c Power R e se a rc h I n s t i t u t e, The p rim a ry o b je c ti v e o f t h i s p r o j e c t i s to d ev e lo p a " c l e a r u n d e rs ta n d in g o f s t r e s s c o r r o s io n c r a c k in g o f F e-n i-c r a l lo y s i n w a te r from room te m p e ra tu re to th e maximum te m p e ra tu re e x p e c te d d u rin g o p e r a tio n o f pow er sy ste m s, The r e s e a r c h work p r e s e n te d i n t h i s t h e s i s i s two f o ld s. The f i r s t i s to d e te rm in e th e e f f e c t, o f d is s o lv e d oxygen, h y d ra z in e, h y d ro g en p e r o x id e, ch ro m ate, n i t r a t e, te m p e ra tu re and a l lo y c o m p o sitio n s on th e c o r r o s io n p o t e n t i a l, o r open c i r c u i t p o t e n t i a l, o f F e-n i-c r a l lo y s. The seco n d i s th e e le c tr o c h e m ic a l s tu d y o f c o rro s io n k i n e t i c s va.th one o f F e-n i-c r a l l o y s, Type 304 s t a i n l e s s s t e e l. The d e t a i l e d e le c tr o c h e m ic a l k i n e t i c s tu d ie s a re th e fo llo w in g s : 1) p o t e n t i o s t a t i c a n o d ic p o l a r i z a t i o n. s tu d ie s w ith e x p e rim e n ta l v a r i a b le s o f te m p e ra tu re ( C ), c o n c e n tr a tio n o f s u l f a t e io n (0,1-0,0 0 1 N) and s c a n r a t e. 2) p o t e n t i o s t a t i c c a th o d ic p o l a r i z a t i o n s tu d ie s v /ith e x p e rim e n ta l v a r i a b l e s o f te m p e ra tu re ( C ), s can r a t e, c o n c e n tr a tio n o f d is s o lv e d oxygen ( ppm) and c o n c e n tr a tio n o f s u l f a t e io n ( ) 3) c u r r e n t decay e x p e rim e n ts v /ith e x p e rim e n ta l v a r i a b le s o f tim e (up to 1,000 m in u te s ), a p p l ie d p o t e n t i a l, te m p e ra tu re ( ^0) and c o n c e n tr a tio n o f s u l f a t e io n (0,1-0,0 1 N ), The c o r r o s io n p o t e n t i a l m easurem ents and e le c tr o c h e m ic a l k i n e t i c s tu d ie s a r e u s e f u l f o r e x p la in in g v/hy Type

22 304 s t a i n l e s s s t e e l e x h i b its s t r e s s c o r r o s io n c ra c k in g i n o x y g en a ted h ig h te m p e ra tu re w a te r. T hese e le c tro c h e m ic a l k i n e t i c m easurem ents a ls o h e lp i n p r e d i c ti n g modes o f c o r r o s io n a t t a c k su ch a s g e n e ra liz e d a t t a c k, l o c a l i z e d a t t a c k, im m unity and p a s s i v i t y. S u p p o rtin g in fo rm a tio n in c lu d in g raw d a ta a r e l i s t e d i n A ppendix,

23 2. THERMODYNAMICS OF IRON-NICKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE WATER 2.1 I n tr o d u c tio n A t y p i c a l therm odynam ic s t a b i l i t y diagram o f m e ta ls i n aqueous s o lu tio n s i s p o te n tia l- p H diagram, som etim es c a l l e d P o u rb a ix d iagram. S in c e th e p u b li c a t io n o f th e P o u rb a ix ^ ^ ^ " A tla s o f E le c tro c h e m ic a l E q u i lib r i a i n Aqueous S o lu tio n s " i n 1963 (E n g lis h e d i tio n i n 1966), th e u s e f u ln e s s o f p o te n tia l- p H s t a b i l i t y d iagram s has been v /e ll re c o g n iz e d. The d iagram s can be d e riv e d e s s e n t i a l l y from a know ledge o f th e s to ic h io m e tr y o f th e r e a c tio n s and f r e e en erg y d a ta f o r th e p a r t i c u l a r s p e c ie s in v o lv e d. R ecent advancem ent o f h ig h te m p e ra tu re h ig h p r e s s u r e e le c tr o c h e m is try s tim u la t e th e e x te n s io n o f th e diagram s to h ig h e r te m p e ra tu re s and p r e s s u r e s. W hile therm odynam ic d a ta, e s p e c i a ll y h e a t c a p a c ity d a ta, fo r p u re p h a s e s a t h ig h e r te m p e ra tu re a r e w e ll docum ented, e x p e rim e n ta l d a ta f o r io n i c s p e c ie s i n aqueous s o lu ti o n a t te m p e ra tu re s, even a s h ig h a s 60 G a r e n o t r e a d i l y a v a ila b l e in th e li te r a tu r & f ^ '^ h i s n eeds th e u se o f e x t r a p o la t io n m ethods o f e s tim a tin g th e f r e e e n e rg ie s o f fo rm a tio n o f aqueous io n s a s a f u n c tio n o f te m p e ra tu re and p r e s s u r e. p o te n tia l- p H diagram f o r th e s u lf u r - w a te r sy stem a t te m p e ra tu r e s up to 230 C by u s in g th e V a n 't H off r e l a t i o n s h i p i n th e form; ^ = A H a ( 1-1 ) - t A l T ^

24 w hich assum es t h a t AH i s in d e p e n d e n t o f te m p e ra tu re. T h is m ethod showed c o n s id e r a b le d is c re p a n c y betw een (21 ) e x p e rim e n ta l f r e e en e rg y v a lu e s and c a lc u la te d o n e s, H elg eso n ^ ^^has shov/n t h a t th e a ssu m p tio n t h a t A cj i s a c o n s ta n t r a t h e r th a n ACp=0 ( i. e. AH in d e p e n d e n t o f te m p e ra tu re ) g iv e s v a lu e s o f f r e e energy change f o r aqueous d is s o c ia tio n r e a c tio n s w hich ai-e c l o s e r to th o s e o b ta in e d e x p e rim e n ta lly, A shw orth and Boden^^) and B rook^^^have com puted th e p o te n tia l- p H diagram s f o r a number o f m e ta ls by c o n s id e r in g th e te m p e ra tu re c o e f f i c i e n t o f e l e c tr o d e p o t e n t i a l, b a se d on th e m ethods A f te r th e p u b li c a t io n o f th e E ntropy C orrespondence P r in c i p le by C r is s an d C o b b le ^ ^ H h e e s tim a te d v a lu e o f h ig h te m p e ra tu re f r e e energ y o f io n ic s p e c ie s w ith t h i s m ethod h as been found to be h ig h ly a c c u r a te P ^ ^ F or l a s t 10 y e a rs t h i s te c h n iq u e h a s been e x te n s iv e ly u sed f o r c o n s tr u c tio n o f p o te n tia l- p H diagram s o f v a rio u s m e ta ls a t te m p e ra tu re s up to 300 C ( i. e. Fe-H 20^^1 )(1 2 ) Fe-HgO-S^^^^ A l-h ^ od^), Cu-SgO^^?), S -H 20(T 8 ), Mn-HgO^^^), Cr-H aoc ^D.and Co-HgoC^Z )), A number o f y e a rs ago M acdonald and B u tle r^ d e v e lo p ed a m o d ifie d v e r s io n o f C r is s and C o b b le 's e x t r a p o la t iv e te c h n iq u e and i s u se d h e re f o r th e c a lc u la tio n o f h ig h te m p e ra tu re f r e e en e rg y o f r e a c tio n s i n Cr-H20 sy stem. The f r e e e n e rg ie s o f fo rm a tio n o f th e s p e c ie s i n Ni-H^O and Fe-H20 sy stem s a t h ig h te m p e ra tu re have been p u b lis h e d by M acdonald e t, a l.p ^ ^ ^ ^ ^ ^ a n d a r e a d o p te d h e re f o r th e c a l c u l a t i o n s.

25 2.2 Thermodynamic Data F or a r e l i a b l e p o te n tia l- p H diagram th e s e l e c t i o n o f therm odynam ic d a ta i s e s s e n t i a l. Thermodynamic d a ta have b ee n com p iled by.m any a u th o r s. F o llo w in g a r e t y p i c a l l i t e r a t u r e s o u rc e s f o r s e l e c t i n g therm odynam ic d a ta, 1, NBS T ech n ical N ote N o.270 Vol. 2. L a tim er 3. P o u rb a ix 4, JM AF T a b le (29) 3. Handbook o f Chem istry and P hysics(^^^ 6, K ubaschew sky and E v a n s (28) 7, H u ltg re n e t. al,(^*^^ 8, E l l i o t and G le i s e r ( 3 1 ) 9, K e lle y (2^^ 10. N icks an d B lock' (27) In s p i t e o f th e above m e n tio n e d l i t e r a t u r e s f o r therm odynam ic d a ta, e n tro p y v a lu e s f o r a number o f s p e c ie s p r e s e n t i n th e aqueous sy stem s a r e o f te n n o t a v a ila b l e in th e l i t e r a t u r e and i t i s, t h e r e f o r e, n e c e s s a ry to o b ta in th e s e m is s in g v a lu e s by e s tim a tio n m eth o d s, L a tim e r(24) d is c u s s e d a m ethod f o r e s tim a tin g th e e n tro p y o f s o l i d compounds and P ow ell and L a tim e r(^ ^ ) d e r iv e d an e q u a tio n f o r e s tim a tin g e n t r o p ie s o f monatomic aqueous io n s. Two e q u a tio n s, by C onnick and P o w e ll(^ ^ )a n d C o u tu re and L a r d le r(^ 4 )^ a r e a v a ila b l e f o r com puting e n tr o p ie s o f o x y a n io n s. A com p ariso n o f e s tim a te d v a lu e s o f e n tro p y to e x p e rim e n ta l v a lu e s was made vrilth s e v e r a l o x y an io n s (s e e T a b le 1 ).

26 T a b le 1, Com parison o f E s tim a te d and E x p e rim e n ta l V alues o f E n tro p ie s, E n tro p y ( c a l /d e g, mol) E s tim a te d (Connick and P ow ell) E x p e rim e n ta l (NBS T e c h n ic a l N ote and ) Chromâte N i t r a t e 3 ^ ^ 3 ^ ^ N i t r i t e S in c e e s tim a te d v a lu e s som etim es showed a c e r t a in d eg ree o f d is c re p a n c y v â th e x p e rim e n ta l v a lu e s, no e s tim a tio n was made f o r th e c o n s tr u c tio n o f p o te n tia l- p H d iagram s o f F e -ifi-c r sy ste m. NBS T e c h n ic a l N ote and w ere u se d f o r f r e e e n e rg y and e n tro p y d a ta and h e a t c a p a c ity d a ta a s a fu n c tio n o f te m p e ra tu re were o b ta in ed from Wicks and Block and K elley^^^^, F or th e therm odynam ic d a ta a t 288 C l i n e a r a p p ro x im a tio n was made betw een 230 C and 300 C, whenever i t i s n ec essary, i. e. e n tro p y p a ra m e te rs f o r C r is s and C o b b le 's e x t r a p o la t iv e m ethod, e t c.. D e ta ils o f th e c a l c u l a t i o n s a re shovra i n A ppendix A.

27 2.3 Results F ig u re s 1 to 5 shows th e p o te n tia l- p H i* e la tio n s h ip o f F e-n i-c r a l lo y s a lo n g vri.th th e s t a b i l i t y domain o f water. The arrov;s i n d i c a t e n e u t r a l ph a t th e te m p e ra tu re, b a s e d on Sv/eeton e t a l. ' s d is s o c ia tio n c o n s ta n t o f w a te r a t h ig h te m p e ra tu r e, 10 ^M o f io n ic a c t i v i t y v/as. ch o sen f o r th e l i n e s o f d is s o lv e d s p e c ie s on th e p o t e n t i a l - ph diagram s. The p o te n tia l- p H r e l a t i o n s h i p o f w a te r s t a b l e domain c o rre s p o n d s to th e e q u ilib r iu m p o t e n t i a l s o f r e a c tio n s (1) (u p p e r l i n e ) and (2 ) (lo w e r l i n e ) a t th e te m p e r a tu r e, 2H2O. = O2 + 4 H^ + l^e ( 1 ) H2 = 2H+ + 2e (2 ) At p o t e n t i a l s g r e a t e r th a n e q u ilib r iu m p o t e n t i a l s f o r r e a c t i o n ( 1 ), i t i s th e rm o d y n am ically p o s s i b le f o r th e e v o lu tio n o f oxygen to o c c u r. L ik e w is e, a t p o t e n t i a l s more n e g a tiv e th a n th e e q u ilib r iu m p o t e n t i a l s f o r r e a c t i o n ( 2 ), i t becom es th e rm o d y n am ically p o s s i b le to ev o lv e h y d ro g en. As th e p r e s s u r e o f th e g aseo u s com ponent in c r e a s e s, th e e q u ilib r iu m p o t e n t i a l s f o r r e a c t i o n s (1 ) and (2 ) become more p o s i t i v e and n e g a tiv e, r e s p e c t i v e l y, i. e. i t becomes th e rm o d y n am ically more d i f f i c u l t to decompose v /a ter i n t o oxygen and h y d ro g en. On th e o th e r hand a t 1 atm, p a r t i a l p r e s s u r e o f hydrogen and oxygen, th e d if f e r e n c e i n e q u ilib r iu m p o t e n t i a l betw een r e a c tio n s (1) an d ( 2 ), and th e r e f o r e, th e re g io n o f s t a b i l i t y o f w a te r, d e c re a s e s from 1,167 V to 1,0 2 2 V a s th e te m p e ra tu re i s in c re a s e d from 100 to 288 C. These d ata d em onstrate

28 t h a t i t hecom es th e rm o d y n a m ic a lly e a s i e r to decompose w a te r w ith in c r e a s in g te m p e r a tu r e. The dependence o f p o t e n t i a l on ph^ i s 2.303H T/F f o r r e a c tio n s (1 ) and (2) an d th e d e c o m p o sitio n v o lta g e o f w a te r ( i, e, E1-E 2 ) i s in d e p e n d e n t o f ph. H owever, th e E/pH^ c o e f f i c i e n t v a r i e s l i n e a r l y w ith te m p e ra tu re and h as n u m e ric a l v a lu e s o f O.O74 V/pH u n i t a t 100 C and 0,111 V/pH u n it at 288 C. The p o te n tia l- p H diagram i s e x te n s iv e ly u se d to r a t i o n a l i z e c o r r o s io n p r o c e s s e s f o r m e ta ls i n aqueous s o lu ti o n. Both c a th o d ic and a n o d ic p ro c e s s e s ta k e p la c e a t th e m e ta l s u r f a c e and th e o v e r a l l c o r r o s io n p r o c e s s i s therm o d y n a m ic a lly p o s s i b le u n d e r th e c o n d itio n s s t a t e d o n ly i f th e e q u ilib r iu m r e a c t i o n p o t e n t i a l f o r th e c a th o d ic p ro c e s s i s more p o s i t i v e th a n th e e q u ilib riu m p o t e n t i a l f o r th e a n o d ic r e a c t i o n. W ith r e f e r e n c e to th e Cr-E^Qi sy stem a t 100 C (F ig u re 1 ), i t i s c l e a r t h a t th e e q u ilib r iu m p o t e n t i a l f o r th e HVH2 ~ re a c tio n i s l e s s p o s i t i v e th a n th e e q u ilib r iu m p o t e n t i a l f o r th e CrO^~'/Cr2pj, r e a c t i o n. T hus, u n d e r th e c o n d itio n s s t a t e d (1 atm. p r e s s u r e o f hydro g en and io n ic a c t i v i t y o f 10 ^M), i t i s n o t p o s s ib le to d is s o lv e chromium o x id e to ch ro m âte io n. H owever, i f th e h ydrogen i n th e system i s re p la c e d by oxygen, th e n th e Og/H^O r e a c tio n can a c t a s th e c a th o d ic p ro c e s s and chromium o x id e w i l l d is s o lv e. S in c e th e d r iv in g fo rc e o f t h i s r e a c t i o n, th e d if f e re n c e i n e q u ilib riu m p o t e n t i a l o f o x id a tio n r e a c t i o n and r e d u c tio n.- r e a c t i o n, i n a l k a l i n e ph i s l a r g e r th a n t h a t i n a c id ph, th e d i s s o lu tio n o f chromium o x id e i n a l k a l i n e s o lu ti o n may be k i n e t i c a l l y more f e a s i b l e i n th e p re s e n c e o f d isso lv e d oxygen. C orrosion o f Ni and Fe i s therm odyna-.

29 10 i m ic a lly p o s s ib le a t ph lo w er th a n n e u t r a l ph i n d e a e ra te d h ig h te m p e ra tu re aqueous s o lu ti o n s. A gain, t h i s d i s s o lu ti o n p ro c e s s may ta k e p la c e more e a s i l y a t lo w e r ph due to th e h ig h e r d riv in g fo rc e o f th e r e a c tio n i n th e s e ph ra n g e s. The e le c tr o c h e m ic a l th e o ry o f m e ta l lic c o r r o s io n can p r e d i c t t h a t th e c o rro s io n p o t e n t i a l a d o p te d by th e m e ta l w ill l i e betw een th e e q u ilib riu m p o t e n t i a l s f o r th e c a th o d ic and. an o d ic p ro c e s s e s and i s c l o s e s t to th e e q u ilib riu m p o t e n t i a l f o r th e p ro c e s s w ith th e h ig h e r exchange c u r r e n t d e n s ity. The p o te n tia l- p H diagram s show t h a t th e s t a b l e re g io n s o f Fe^"^ and Ni^"^ d e c re a s e m ark ed ly a t h ig h e r te m p e ra tu re. T h is in d i c a t e t h a t a c id s t a b i l i t y o f Fe and Hi in c r e a s e s w ith te m p e ra tu re. The e q u ilib riu m p o t e n t i a l s f o r th e H i^ ^ /N i and F e^v F e co u p le s change from V to V and from -0,6 1 9 V to -0,7 0 7 V on in c r e a s in g th e te m p e ra tu re from 100 C to 288 C, r e s p e c t i v e l y. Thus, c a th o d ic p r o te c ti o n o f n ic k e l and ir o n i n a c id ic s o lu tio n s may be more d i f f i c u l t a t th e h ig h e r te m p e ra tu re.

30 N i O ,=1 atm: N i O ph a t TOOOC Figure 1, Potential-pH diagram of Fe-Ni-Cr'HgO at 100 C

31 CrOi NiO ph a t 15Q0C Figure 2* Potential-pH diagram of Fe-Wi-Cr-H20 at 1$0 C

32 scro; W l ^ e F ig u re,3. P o ten tial-p H diagram o f Fe-Ni-Cr-H^O a t 200 C

33 ph a t 250OC Figure,4. Potential-pH diagram of Fe-Ni-Cr-HgO at 250 C

34 CrO^ o CrC ph a t 2880C Figure. 5. Potential-pH diagram of Fe-Ni-Cr-H2Û at 288 C

35 3. CORROSION POTENTIAL OF IRON-NIGKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE OXYGENATED WATER 3,1 I n tr o d u c tio n I n n e u t r a l o r b a s ic aqueous s o lu ti o n s th e p rim ary c a th o d ic r e a c tio n i s oxygen r e d u c tio n r e a c tio n in th e a b se n c e o f o th e r o x id iz in g s p e c ie s b e c a u se o f low c o n c e n tr a tio n o f hydrogen io n. Removal o f d is s o lv e d oxygen from w a te r h as been a m a jo r i s s u e o f m in im izin g c o r r o s io n o f i r o n o r s t e e l i n b o i l e r w a te r. A lso, r e c e n tly h ig h p u r i t y w a te r h a s been u s e d i n b o ilin.g w a te r n u c le a r r e a c t o r (BV/R) a s a c o o la n t and a u s t e n i t i c s t a i n l e s s s t e e l h as been a m ajo r c o n s tr u c tio n m a t e r i a l. A fte r a num ber o f y e a r s o f s e r v ic e s t r e s s c o r r o s io n c ra c k in g o f a u s t e n i t i c s t a i n l e s s s t e e l i n BWR h as been a problem. I t was found t h a t s t r e s s c o r r o s io n c ra c k in g o f a u s t e n i t i c s t a i n l e s s s t e e l i n BWR i s c l o s e ly r e l a t e d to th e amount o f d is s o lv e d oxygen and o th e r o x id iz in g s p e c ie s p r e s e n t i n c o o la n t w a te r. T h is s tu d y in v e s t i g a t e d th e e f f e c t o f d is s o lv e d oxygen c o n c e n tr a tio n on c o r r o s io n p o t e n t i a l o f s e v e r a l F e-n i-c r a l lo y s a t te m p e ra tu re s C. A number o f i n v e s t i g a t i o n s have m easured th e c o r r o s io n p o t e n t i a l o f th e s e a l lo y s i n h ig h te m p e rtu re o x y g en a ted w ate rp ^ "-^ ^ ^ A lthough t h e i r r e s u l t s showed same g e n e ra l tr e n d s, th e q u a n t i t a t i v e ag reem en t was r a t h e r p o o r. T hese r e s u l t s w ere a n a ly z e d on th e b a s is o f i n l e t oxygen c o n c e n tr a tio n, w h ile o u t l e t oxygen c o n c e n tr a tio n h a s been r e a l i z e d to 16 '

36 be e q u a lly im p o rta n t due to th e consum ption o f oxygen in th e sy ste m. More r e c e n t l y In d ig and M c l l r e e ^ ^ s tu d ie d th e e f f e c t o f d is s o lv e d oxygen c o n c e n tr a tio n on th e 17 c o r r o s io n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l i n tita n iu m a u to c la v e a t 274 C to m in im ize th e oxygen consum ption on th e w a ll o f a u to c la v e. I n s p i t e o f th e above m entio n ed a tte m p ts a more s y s te m a tic s tu d y o f t h i s a r e a was n eeded due to i t s p r a c t i c a l im p o rta n c e, 3.2 T heory o f Oxygen E le c tro d e The e le c tr o c h e m is tr y o f oxygen h as b ee n rev iev /ed by a number o f authors^following a r e summary o f Vifill s^^^^ r e c e n t re v ie w o f th e oxygen e l e c tr o d e. The s ta n d a r d p o t e n t i a l o f th e oxygen e l e c tr o d e ( th e d if f e r e n c e betw een e q u ilib r iu m p o t e n t i a l o f O2/H 2O r e a c t i o n and HVH^ r e a c t i o n ), m entio n ed i n C h ap ter 2, i s E =.l,l6 7 V a t 100 C an d 1,0 2 2 V a t 288 C. The dependence o f th e oxygen e l e c tr o d e r e a c t i o n H'* + 4e = 2H2O ( in ac id ) O2 + 2H2O + 4e = 40H ( i n a l k a l i ) on ph and oxygen p a r t i a l p r e s s u r e a t te m p e ra tu re T i s giv en by Erp = eç - ~ ph + lo g pq^ (V o lts ) The r e v e r s i b l e oxygen p o t e n t i a l a c c o rd in g to th e above e q u a tio n s h o u ld be e s t a b l i s h e d i f no o th e r r e a c t i o n s, su ch a s m e ta l d i s s o l u t i o n, o x id e fo rm a tio n, fo rm a tio n o f o th e r r e a c t a n t s an d re d o x r e a c tio n s in v o lv in g im p u r iti e s, would occur a t r a te s com parable to o r la r g e r than th e

37 18 O2/H 2O r e a c t i o n. T hese c o n d itio n s v/ould r e q u i r e a c o m p le te ly i n e r t, c a t a l y t i c a l l y v e r y a c t i v e e le c tr o d e i n a h ig h ly p u r i f i e d s o lu ti o n. Such c o n d itio n s have n e v e r b een m ainta in e d f o r more th a n a few h o u rs and i t i s a w ell-know n f a c t t h a t th e r e v e r s i b l e oxygen e le c tr o d e p o t e n t i a l h a s n o t been o b s e rv e d fo r e x te n d e d p e r io d s o f tim e a t o r n e a r room te m p e r a tu r e. Only i n r a r e c irc u m s ta n c e s have t r a n s i e n t v a lu e s c lo s e to V, e q u ilib riu m p o t e n t i a l o f oxygen e le c tr o d e a t 2$ C, been a c h ie v e d on p la tin u m i n s u l f u r i c a c id a f t e r p ro lo n g e d ch e m ic a l o x id a tio n and p r e - a n o d i z a t io n, o r a f t e r h ig h te m p e ra tu re o x id a tio n and n i t r i c a c id p a s s iv a t io n co u p led w ith e x te n s iv e p r e - e l e c t r o l y s i s o f th e e l e c t r o l y t e. T hus, i t a p p e a rs t h a t th e r e v e r s i b l e oxygen p o t e n t i a l can be o b ta in e d f o r s h o r t p e r io d s o f tim e and u n d e r v ery s e l e c t e d c o n d itio n s, b u t th e s e cond it io n s do n o t re p r e s e n t: a s te a d y s t a t e. U nder a l l b u t th e s p e c i f i c c o n d itio n s m e n tio n e d above, th e r e v e r s i b l e oxygen p o t e n t i a l i s n o t o b s e rv e d a t o r n e a r room te m p e ra tu re even i f th e most s t r i n g e n t p u r it y c o n d itio n s a r e a p p lie d to th e e l e c t r o l y t e. I n s te a d, r e s t p o t e n t i a l s, E^, (on open c i r c u i t ) a r e o b s e rv e d w hich l i e betw een 0.7 and 1.1 V and te n d to d r i f t w ith tim e. F u rth e rm o re, th e m a gnitude o f th e r e s t p o t e n t i a l s i s s tr o n g ly a f f e c te d by th e e le c tr o d e m a te r i a l, th e e le c tr o d e p r e tre a tm e n t, th e ph and s t i r r i n g o f th e e l e c t r o l y t e. Hydrogen p e r o x id e, u s u a ll y form ed a s a r e a c tio n in te r m e d ia te i n th e oxygen r e d u c tio n p r o c e s s, s i g n i f i c a n t l y a f f e c t s th e r e s t p o t e n t i a l and th e e f f e c t o f m e ta l o x id e fo rm a tio n o r m e ta l d i s s o lu ti o n h a s been e s ta b lis h e d on a t l e a s t a few m e ta ls. Thus, th e v a r io u s

38 f a c t o r s in f lu e n c in g th e oxygen r e s t p o t e n t i a l can be 19 : r a t i o n a l i z e d on th e b a s is o f th e m ixed p o t e n t i a l c o n c e p t, o r i g i n a l l y p ro p o sed by Wagner and T ra u d. The Pq^ - dependence i s g e n e ra lly e x p e c te d to be d i f f e r e n t from th e BT/^F (V) change p e r decade c h a r a c t e r i s t i c f o r th e r e v e r s i b l e oxygen e l e c tr o d e, 5,3 Experim ental 5,3,1 D escrip tio n o f E xperim ental System The e x p e rim e n ta l s e tu p i s shovm i n F ig u re 6, where th e p e r t i n e n t com ponents a r e i d e n t i f i e d. The th r e e ta n k s (n o s, 5,6 and 7) and in t e r c o n n e c tin g tu b in g from ta n k no, 7 to h ig h p r e s s u r e pump w ere c o n s tr u c te d o f Type 304 s t a i n l e s s s t e e l, w hereas th e p r e h e a te r tu b in g, a u to c la v e and a f t e r - c o o l e r w ere made o f In c o n e l 600, Tank n o. 1 w hich s to r e d d i s t i l l e d w a te r v/as t i n l i n e d. I n te r c o n n e c tin g tu b in g from t h i s ta n k th ro u g h th e M illip o r e w a te r p u r i f i c a t i o n sy stem and up to ta n k n o. 5 v;as made o f p o ly v in y lc h lo r id e. The M illip o r e w a te r p u r i f i c a t i o n system p ro v id e d w a te r o f 18 Mohm/cm s p e c i f i c r e s i s t i v i t y. T h is w a te r p u r i f i c a t i o n sy stem c o n ta in e d fo u r r e p la c e a b le c a r t r i d g e e le m e n ts, o p e r a tin g i n s e r i e s to p ro v id e p r e f i l t r a t i o n, o r g a n ic s a d s o r p tio n and d e io n iz a tio n. S p e c ific r e s i s t i v i t y o f w a te r i n fe e d ta n k (n o, 7) was a ls o m easured vn.th Beckman c o n d u c tiv ity m e te r, Model BC-I6C, and was found to be 4-6 Mohm/cm due to p re s e n c e o f oxygen and p o s s ib ly c o r r o s io n p ro d u c ts from th e ta n k s. D is so lv e d oxygen in ta n k s n o s, 6 and 7 was c o n t r o lle d by p u rg in g th e ta n k s w ith a p ro p e r a rg o n and oxygen m ix tu re. Argon and oxygen were mixed in th e d e sire d r a tio by

39 20 c o n t r o lli n g t h e i r flow r a t e s th ro u g h a M atheson g as p r o p o r tio n e r (M odel Wo, 7352T ). The oxygen c o n c e n tr a tio n i n th e fe e d ta n k was k e p t c o n s ta n t d u rin g a t e s t p e r io d, W ater was pumped from th e fe e d ta n k th ro u g h th e re m a in d e r o f th e sy stem by a Yarway C yclo/p hram h ig h p r e s s u r e pump (Model B) w ith flow r a t e o f 4 l i t e r / h o u r. The w a te r was h e a te d by p a s s in g i t th ro u g h p r e h e a te r tu b in g p r i o r to e n te r in g th e a u to c la v e. T h is e lim in a te d th e rm a l zones v /ith in th e a u to c la v e,. The a u to c la v e was a. 4 l i t e r double b o lt e d c lo s u r e v e s s e l, W ater le a v in g th e a u to c la v e p a s s e d th ro u g h a a f t e r - c o o l e r. The c o o le r c o n s is te d o f 2? m o f c o i le d in c o n e l 600 tu b in g. The w a te r l e f t th e h ig h p r e s s u r e sy stem a t th e back p r e s s u r e r e g u l a t o r. T h is c o n s is te d o f a s p r in g s e a l a t w hich th e h ig h p r e s s u r e pump m ust push a g a in s t. System p r e s s u r e was a b o u t 80 P a tm,(= p s i), S in c e th e flow r a t e th ro u g h th e a u to c la v e was n o t s u f f i c i e n t to fe e d th e e x i t oxygen a n a ly z e r a t 250 m l/m in,, as r e q u ir e d by th e Beckman i n s t r u c t i o n m anual, a 4 l i t e r h old u p tanic w ith a m icro-pum p was i n s t a l l e d a t th e e x i t to p ro v id e th e 250 m l/m in. c i r c u l a t i o n th ro u g h th e a n a ly z e r. P h o to g rap h s o f in d i v id u a l com ponents o f th e system a r e shov/n i n A ppendix.0, ^ 5,5.2 Specimen P re p a ra tio n and Measurement M a te r ia ls i n th e stu d y w ere P t, N i, C r, Type 504 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800, C o m p o sitio n, th e rm a l h i s t o r y and m ic r o s tr u c tu r e o f th e m a te r i a ls a r e l i s t e d i n A ppendix B, C y lin d r ic a l specim ens (6 mm d ia.x 12 mm lo n g ) m ounted on T e flo n c o a te d s t a i n l e s s s t e e l holderwere u s e d up to 250 C, B ecause o f its-'^ u n s ta b le n a tu r e o f T e flo n c o a tin g a t 288^0 m e ta l ro d e le c tr o d e s

40 v/ere u sed a t t h i s te m p e ra tu re ( s e e F ig u re 7)* From F ig u re s 8 an d 9 i t was v e r i f i e d t h a t th e change i n e le c tr o d e c o n f ig u r a tio n d id n o t a f f e c t th e c o r r o s io n p o t e n t i a l o f th e specim en s i g n i f i c a n t l y. The d if f e r e n c e v;as o n ly ^20 mv. An i n t e r n a l Ag/AgCl e l e c tr o d e w ith 0,01 N KOI s o lu tio n v/as a r e f e r e n c e e l e c tr o d e f o r m e asu rin g c o r r o s io n p o t e n t i a l s o f th e sp e c im e n s. D e ta ils o f th e Ag/AgCl re f e r e n c e e le c tr o d e a r e d e s c r ib e d i n th e fo llo v /in g s e c t io n, A f r e s h s e t o f sp ecim en s an d r e f e r e n c e e l e c tr o d e was u se d f o r each e x p e rim e n t. The sp ecim en s w ere p o lis h e d w ith 600 g r i t s i l i c o n c a rb id e p a p e r th e n c le a n e d w ith a c e to n e and d i s t i l l e d w a te r p r i o r to p la c in g them i n th e a u to c la v e, K e ith le y Model 602 e le c tr o m e te r was u sed vri.th a d a ta ;-p le x e r f o r m e a su rin g th e c o r r o s io n p o t e n t i a l s o f th e specim ens in a s e t sequence, 21! R e fe re n c e E le c tro d e The m ost p o p u la r i n t e r n a l r e f e r n e e e le c tr o d e f o r e le c tro c h e m ic a l m easurem ents i n h ig h te m p e ra tu re h ig h p r e s s u r e aqueous s o lu ti o n i s Ag/AgCl e l e c tr o d e. S e v e ra l d e s ig n s o f t h i s r e f e r e n c e e le c tr o d e have been d e s c rib e d i n th e lite r a tu r e ^ ^ ^ ^ " ^ ^ ^ ^ A g ra w a l's d e s ig n ^ ^ ^ ^ w ith a s l i g h t m o d if ic a tio n was u s e d f o r th e p r e s e n t s tu d y. The sc h e m a tic diagram and p h o to g ra p h o f th e Ag/AgCl r e f e r e n c e e le c tr o d e a r e shovra i n F ig u re 30 and 3 1, r e s p e c t i v e l y. B ackground: The standard electrode potential, E, at 23 to 300 C with hydrogen scale has been established by Greeley, et. a l,, They used a Type 347 stainless steel autoclave

41 22 ; v /ith a fu s e d s i l i c a l i n e r f o r th e t e s t. The p o t e n t i a l o f Ag/AgCl e le c tr o d e was m easu red a g a in s t P t/h 2 e le c tr o d e a tm.) in v a r io u s c o n c e n tr a t io n s o f h y d ro c h lo ric a c id (0.0 0 $ -1.0 M). The m easurem ents w ere r e p r o d u c ib le to w ith in ± 0.5 mv from 2$ to 225 C, ±2 mv a t 250 C and ±5 mv a t 275 C, The r e s u l t i n g e q u a tio n f o r th e s ta n d a r d p o t e n t i a l o f th e Ag/AgCl e le c tr o d e i s E = x10-4 t x 1Q -^ t2, w here E i n V o lts and t i n C. The e x p e rim e n ta l v a lu e s o f s ta n d a r d p o t e n t i a l o f Ag/AgCl e l e c tr o d e a g re e w ell v /ith th e c a lc u la te d therm odynam ic r e v e r s i b l e p o t e n t i a l, b a s e d on C r is s and C o b b le 's e x t r a p o l a t i v e p r in c ip le d ^ T hese two r e s u l t s a r e ^om pared i n F ig u re 32. The E and t \ j h a l f c e l l p o t e n t i a l E f o r th e A g/agcl/o.0 1 M KCl e l e c tr o d e c a l c u l a t e d a t d i f f e r e n t te m p e ra tu re s u s in g th e r e l a t i o n s h i l g iv e n by G re e le y e t. a l. and th e W ernst e q u a tio n a re p l o t t e d i n F ig u re 33. E le c tro d e P r e p a r a tio n : A s i l v e r r o d o f 3 mm d ia, was swaged on one end to re d u c e i t s d ia m e te r to a b o u t 1 mm. T h is ro d was p o lis h e d w ith 600 g r i t s i l i c o n c a rb id e p a p e r and th e n r in s e d w ith a c e to % and d i s t i l l e d w a te r. The ro d was p l a c e d i n a IN' h y d r o c h lo r ic a c id s o lu ti o n and co n n e c te d to a D. C. pov/er s u p p ly and a p la tin u m e le c tr o d e. The s i l v e r ro d was an anode and p la tin u m was a cath o d e to c h l o r id iz e th e s i l v e r r o d. I n i t i a l c u r r e n t a p p lie d was low, 2-3 ma, f o r b e t t e r ad h e re n c e o f s i l v e r c h lo r id e d e p o s it on s i l v e r ro d, th e n in c r e a s e d up to 20 ma f o r 5 to 10 h o u rs. The s i l v e r ro d was th o ro u g h ly w ashed w ith d i s t i l l e d v /a te r a f t e r c h l o r i d i z a t i o n. The

42 23 s i l v e r ro d v;as w rapped w ith t h i n T e flo n ta p e b e fo re p la c in g i t in t o T e flo n e le c tr o d e cham ber. T h is m inim ized th e p o s s i b i l i t y o f m icro -1 ealc th ro u g h th e i n t e r f a c e betw een s i l v e r ro d and T e flo n e le c tr o d e cham ber due to th e s u r f a c e i r r e g u l a r i t y o f s i l v e r r o d when e le c tr o d e was p la c e d i n h ig h te m p e ra tu re p r e s s u r iz e d w a te r. The m ic r o -le a k, o f te n n o t v i s i b l e, c o u ld ca u se changes i n c h lo r id e a c t i v i t y i n th e e le c tr o d e cham ber, and th u s change th e e l e c tr o d e p o t e n t i a l. The le n g th w rapped was a b o u t 10 cm from to p o f th e ro d. The e l e c tr o d e cham ber w ith s i l v e r ro d was assem b led i n two Conax f i t t i n g s w ith s t a i n l e s s s t e e l c o u p lin g and a n u t p ro p e rly tig h te n e d. The cham ber was f i l l e d w ith z i r c o n ia san d t h a t was p re so ak ed in 0.01 M KCl s o lu ti o n, th e n th e cham ber was c lo s e d w ith a p o ro u s z i r c o n ia p lu g. The p a r t i a l l y assem b led re f e r e n c e e le c tr o d e was ch eck ed a t t h i s p o in t a g a in s t a s à tu r.a të d calo m el e le c tr o d e f o r th e a c c u ra c y o f c e l l p o te n tia l which should be The assem bly o f b u ffe r com partm ent was th e n e x t s te p. S t a b i l i t y : The s t a b i l i t y o f Ag/AgCl r e f e r e n c e e le c tr o d e was checked by m e asu rin g th e p o t e n t i a l a t room te m p e ra tu re w ith s a tu r a te d calo m el e le c tr o d e a f t e r each t e s t. The r e l i a b i l i t y o f e le c tr o d e was found to be s tr o n g ly dep enden t on te m p e ra tu re. At 100 C th e e l e c tr o d e l a s t e d f o r 10 days w ith o u t a p p re c ia b le d r i f t i n p o t e n t i a l (<10mV), b u t th e tim e was s h o r te r a b o u t 4 to 3 days a t 250 C (±20 mv c h a n g e ). The d r i f t o f p o t e n t i a l v/as even g r e a t e r

43 a t 288 C, and th e p o t e n t i a l v/as n o t s ta b l e a f t e r s e v e r a l h o u rs o r a day a t t h i s te m p e ra tu re. The s t a b i l i t y o f 24 Ag/AgCl e le c tr o d e v/as a ls o a f f e c te d by th e p r e p a r a tio n te c h n iq u e. Any c a r e le s s p r e p a r a tio n s i g n i f i c a n t l y re d u c e d th e d u r a b i l i t y o f th e e l e c tr o d e. 3,3. 4 Oxygen A n a ly s is To in s u r e th e c o n s ta n c y o f d is s o lv e d oxygen conc e n tr a ti o n th ro u g h o u t th e e x p e rim en t oxygen c o n c e n tr a tio n was m o n ito re d c o n tin u o u s ly v /ith Beckman oxygen a n a ly z e r, M odel 735X, w hich i s b a s i c a l l y an oxygen e l e c tr o d e. Oxygen s e n s o r f o r th e in s tru m e n t c o n s is ts o f a g o ld c a th o d e,a s i l v e r anode, a T e flo n membrane and 4^ KCl s o lu tio n betw een th e e le c tr o d e s. As th e w a te r im p in g es on th e membrane some o f th e d is s o lv e d oxygen d if f u s e s thro ug h th e T eflon membrane, th is oxygen re a c ts on th e cath o de and p ro d u ces OH io n s. A s m a ll c u r r e n t v/hich i s p r o p o r tio n a l to th e d is s o lv e d oxygen i n th e w ate r r e s u l t s. The c u r r e n t i s a m p lifie d an d c a l i b r a t e d to g iv e a s ig n a l p r o p o r tio n a l to th e d is s o lv e d oxygen O2 + 2H2O + 4e = 4OH 4Ag + 4CI = 4AgCl + l+e a t th e cathode a t th e anode At th e end o f each e x p e rim en t i n l e t and o u t l e t oxygen c o n c e n tr a tio n s w ere a n a ly z e d w ith ' c h e m ical te c h n iq u e s. F or d is s o lv e d oxygen c o n c e n tr a tio n s above 170 ppb s ta n d a r d W inkler te c h n iq u e, d e s c rib e d i n M ethod D, ASTM S ta n d a rd D ^^^^and f o r th e oxygen c o n c e n tr a tio n s below 170 ppb c o lo r im e tr ic in d ig o -c a rm in e te c h n iq u e w ere u sed. Sam pling o f v /ater fo r in digo-carm in e method

44 fo llo w e d J o n e s m ethod^^^^but i n s t e a d o f u s in g e v a c u a te d v e s s e l. a 100 ml sam p lin g c o n t a in e r was p u rg ed w ith p re p u r i f i e d arg o n f o r a b o u t 30 m in u te s p r i o r to c o l l e c t i n g sam p le. M ethod A i n ASTM S ta n d a rd D888-66^^^^was a d o p te d 25 f o r c o lo r s ta n d a rd s o f up to 60 ppb d is s o lv e d oxygen c o n c e n tr a tio n s, and f o r c o lo r s ta n d a r d s o f oxygen conc e n tr a ti o n s betv/een 60 ppb and 170 ppb B uchoff e t. a l. *s^^^^ m ethod v/as u s e d. The c o l o r im e tr ic in d ig o -c a rm in e m ethod i s b a s i c a l l y a com parison m ethod o f th e c o lo r d evelo p ed by th e o x id a tio n o f re d u c e d in d ig o c a rm in e. Upon o x id a tio n th e b r i g h t y e llo w -g re e n c o lo r o f re d u c e d in d ig o carm ine changes to o ra n g e, to r e d, to p u r p le, to b lu e and f i n a l l y to b lu e -g re e n i n th e c o m p le te ly o x id iz e d form. The W inkler te c h n iq u e f o r d is s o lv e d oxygen a n a ly s is i s a t i t r a t i o n m ethod. F r e s h ly p r e c i p i t a t e d manganous h y d ro x id e r e a c t s v /ith th e d is s o lv e d oxygen p r e s e n t to form an in s o lu b l e compound c o n ta in in g m anganese i n a h ig h e r s t a t e o f o x id a tio n. On ad d in g an e x c e ss o f a c id i n th e p re s e n c e o f a s u b s ta n c e w hich i s " r e a d i l y o x id iz e d (s u c h a s io d id e io n ), th e p r e c i p i t a t e d is s o lv e s and th e m anganese i s re d u c e d to th e o r i g i n a l d iv a le n t form ; an e q u iv a le n t amount o f io d in e i s l i b e r a t e d. Mn^*+ 20H = MnCOH)^ 2Mn(0H)2+ 0^ = 2MnO(OH)g Mn0(0H)2+ 21"+ Ig+ Mn^ ^+ 3 H2 O The l i b e r a t e d io d in e i s t i t r a t e d w ith s ta n d a r d sodium t h i o s u l f a t e s o lu tio n u s in g s t a r c h i n d i c a t o r.

45 26 : 3. if Results C o rro s io n p o t e n t i a l s o f th e a l lo y s v/ere m easured a t 100, 150, 200, 250 and 288 C. The oxygen c o n c e n tr a tio n v a r ie d w ith th e t e s t from a low o f 3 PPh to a h ig h o f 8 ppm» F ig u re 10 shows a. t y p i c a l c o r r o s io n p o t e n t i a l r e s ponses o f th e v a rio u s m e ta ls a t 288 C i n o x y g e n a te d v;ater VD.th tim e. In t h i s c a se s te a d y s t a t e was re a c h e d i n a b o u t 20 h o u rs, w h ile o th e r s showed th e tim e f o r th e p o t e n t i a l to re a c h s te a d y s t a t e depended on b o th te m p e ra tu re and oxygen c o n c e n tr a tio n and g e n e r a lly was a b o u t h o u rs H owever, w ith in te r m e d ia te oxygen c o n c e n tr a tio n s a t lo w e r te m p e ra tu re s th e tim e was lo n g e r up to 60 h o u rs. To in s u r e th e s te a d y s t a t e v a lu e o f th e c o r r o s io n p o t e n t i a l fo r lo n g e r p e rio d o f ex p e rim e n t one s e t o f experim ent v;as made fo r 200 hours a t 250 C ( see F igu re 11), Not much change i n c o r r o s io n p o t e n t i a l s o f th e m e ta ls was o b serv e d a f t e r 50 h o u rs. The p o t e n t i a l was c o n s id e re d s te a d y i f th e v a lu e was w ith in ±5 mv f o r 5 to 10 h o u rs, ph 's o f i n l e t and o u t l e t w a te r w ere a l s o m easured w ith Beclnnan Model 3550 d i g i t a l ph m e te r a t room te m p e ra tu re and w ere found to be n e a r l y same i n m ost c a s e s,t h e v a lu e s w ere c lo s e to n e u t r a l ph. C o rro s io n p o t e n t i a l s o f th e a l lo y s w ith r e s p e c t to oxygen c o n c e n tr a tio n a r e shown i n F ig u re s 12 to 17. I t was found t h a t th e i n l e t and o u t l e t oxygen c o n c e n tr a tio n s w ere d i f f e r e n t and th e d if f e r e n c e was p a r t i c u l a r l y p ro nounced a t lo w er oxygen c o n c e n tr a tio n s and h ig h e r tem p erat u r e s, To m inim ize t h i s u n c e r t a in t y th e oxygen c o n c e n tr a tio n

46 27 : a f t e r p r e h e a te r was a n a ly z e d by e i t h e r W inkler method o r in d ig o -c a rm in e c o l o r im e tr ic m ethod, w hich w ere d e s c rib e d i n th e p re v io u s s e c t i o n. W ater sam ples w ere ta k e n th ro u g h a b y -p a s s l i n e a t th e end o f each e x p e rim e n t, T h is v a lu e r e p r e s e n t s th e a c tu a l i n l e t oxygen c o n c e n tr a tio n o f a u to c la v e. At te m p e ra tu re s lo w er th a n 250 C th e oxygen consum ption was m ainly ta k in g p la ce in th e p reh e a t e r. In F ig u re s 12 to 1? th e d a ta p o in ts a r e b a sed on th e oxygen c o n c e n tr a tio n a f t e r p r e h e a te r and th e a rro w s in d i c a t e th e o u t l e t c o n c e n tr a tio n s o f oxygen. In a l l c a s e s th e c o r r o s io n p o t e n t i a l in c r e a s e d v/ith oxygen c o n c e n tr a tio n. The i n c r e a s e in p o t e n t i a l from a low oxygen ( - 3 P P b ) to a liig h oxygen 1,000 ppb) was app rox im ately 600 mv fo r m ost o f th e m etals, R e la tiv e ly sm all changes were observed a t oxygen conc e n t r a t i o n s above 1,000 ppb. The e f f e c t o f te m p e ra tu re was to s h i f t th e c o r r o s io n p o t e n t i a l o f th e specim ens to w ard s th e a c t i v e s i d e. The drop i n p o t e n t i a l w ith te m p e ra tu re was m ost s i g n i f i c a n t f o r P t i n com parison to th e F e-n i-c r a l lo y sp e c im e n s. F ig u re 18 shows th e e f f e c t o f a l l o y c o m p o sitio n s on th e c o r ro s io n p o t e n t i a l o f th e s e a l lo y s a t 250 C a lo n g w ith th e therm odynam ic e q u ilib r iu m p o t e n t i a l s o f th e oxygen e le c tr o d e and th e hydrogen e l e c tr o d e, r e s p e c t i v e l y. T hese e q u ilib r iu m p o t e n t i a l s a re b ased on n e u tra l ph (= 3,33). At th e oxygen concent r a t i o n s below 10 ppb and above 1,000 ppb a l l F e-n i-c r a l lo y s have e s s e n t i a l l y th e same c o rro s io n p o t e n t i a l w h ile a t in te r m e d ia te oxygen c o n c e n tr a tio n s th e c o r ro s io n p o t e n t i a l s o f th e a l lo y s a r e somewhat d is p e r s e d. The p o t e n t i a l o f P t shows th e h ig h e s t v a lu e a t a l l te m p e ra tu re s and oxygen c o n c e n tr a t io n s. The lo w e s t p o t e n t i a l was f o r

47 Cr i n m ost in s ta n c e s. The p o t e n t i a l s o f o th e r a l lo y s w ere between th a t of P t and Cr. 28 In o rd e r to d e te rm in e v /h e th er th e c o rro s io n p o t e n t i a l o f th e m e ta ls i s r e v e r s i b l e w ith r e s p e c t to te m p e ra tu re and oxygen p e r t u r b a tio n s i n th e sy stem, two s e t s o f e x p e riments were conducted. In th e f i r s t s e t th e oxygen concent r a t i o n was f ix e d and th e te m p e ra tu re was c y c le d. The c o rro s io n p o t e n t i a l was m easured a t an i n i t i a l low te m p eratu r e u n t i l i t became s te a d y i n ab o u t 30 h o u rs, and th e n th e te m p e ra tu re o f th e system was r a i s e d to 230 C and th e p o t e n t i a l was a llo w e d to a t t a i n a new s te a d y s t a t e v a lu e. Then th e te m p e ra tu re was lo w e re d to th e i n i t i a l v a lu e and th e m easurem ents w ere made f o r a n o th e r 30 h o u rs. The r e s u l t s fo r low (^3 ppb) oxygen w a te r a r e shown i n F ig u re 19 and t h a t f o r h ig h (6-7 ppm) oxygen w a te r i n F ig u re 20. W ith an in c r e a s e i n te m p e ra tu re to 230 C th e s te a d y s t a t e v a lu e s o f c o r r o s io n p o t e n t i a l w ere, a s e x p e c te d, th e same a s v a lu e s r e p r e s e n t a t i v e o f th e te m p e r a tu r e, as shov/n i n F ig u re s 12 to 17. As shown in F ig u re 19 n i c k e l. Type 30k and In c o n e l 600 reassu m ed t h e i r o r i g i n a l c o r r o s io n p o t e n t i a l s, vri.thin -1 0 mv, a f t e r th e te m p e ra tu re was c y c le d back to th e o r i g i n a l 130 C. P la tin u m and In c o lo y 800 a t t a i n e d new c o r r o s io n p o t e n t i a l s w hich w ere s l i g h t l y (<30 mv) lo w er th a n th e o r i g i n a l v a lu e s, b u t chromium showed a la r g e drop o f a p p ro x i m a te ly 200 mv. In th e h ig h oxygen w a te r. F ig u re 20, a l l th e m e ta ls, e x c e p t chrom ium, reassu m ed t h e i r o r i g i n a l s te a d y s t a t e v a lu e s a f t e r th e te m p e ra tu re p e r t u r b a tio n. Chromium showed a 100 mv h ig h e r v a lu e th a n e x p e c te d a t 175 C. The e f f e c t o f th e oxygen c o n c e n tr a tio n p e r t u r b a tio n on th e c o r r o s io n p o t e n t i a l was s tu d ie d a t 130 C and 230 C i n th e

48 seco n d s e t o f e x p e rim e n ts. The r e s u l t s f o r 150 C a r e shovm 29 ' in F ig u re 21 and th o s e f o r 250 C in F ig u re 22. In th e s e two c a se s th e i n i t i a l and th e f i n a l oxygen c o n c e n tr a tio n i n th e w a te r was 10 ppb; th e p e r t u r b a tio n c o n c e n tr a tio n was 2.2 ppm a t 190 C and 1.3 Ppm a t 230 C. The s te a d y s t a t e v a lu e s o f th e c o r r o s io n p o t e n t i a l w ith th e new oxygen conc e n tr a tio n s w ere as e x p e c te d from th e F ig u re s 12 to 17. At 230 C when th e p e r t u r b a tio n was rem oved, th e c o rro s io n p o t e n t i a l v a lu e s r e t u r n e d to vri.thin ±20 mv f o r N i, Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800, b u t o n ly to w ith in ±50 mv f o r Cr and P t. At 150^0 th e r e t u r n o f th e c o rro s io n p o t e n t i a l, a f t e r th e p e r t u r b a tio n was rem oved, to o k lo n g e r ( 40 h r s. ) th a n th e u s u a l 20 h o u rs. The re c o v e ry was o n ly to v /ith in ±50 mv o f th e o r i g i n a l v a lu e s f o r N i, P t, Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and Inco lo y 800, and 200 mv fo r chromium. The above e x p e rim e n ta l r e s u l t s s u g g e s t t h a t th e c o rro s io n p o t e n t i a l o f P t, N i, Type 304 s t a i n l e s s s t e e l, In c o lo y 800 and In c o n e l 600 a r e f a i r l y r e v e r s i b l e w ith r e s p e c t to te m p e ra tu re and oxygen p e r t u r b a tio n s i n w a te r. I t a p p e a rs th a t a t h ig h te m p e ra tu re (250 C ) th e e q u ilib riu m c o n d itio n s a re a t t a i n e d q u ic k ly b e c a u se o f th e in c r e a s e d k i n e t i c s, b u t th e k i n e t i c s a r e r e l a t i v e l y slow a t 150 C.

49 3.5 D iscussion 30 ' 3,3.1 Com parison o f E x p e rim e n ta l D ata v jith Thermodynamic E q u ilib riu m P o t e n t i a l o f Oxygen E le c tro d e, Hydrogen E le c tro d e and F e-n i-c r A llo y s, F ig u re s 23 and 24 show th e e q u ilib riu m p o t e n t i a l s o f oxygen e le c tr o d e and hydro g en e le c tr o d e a t te m p e ra tu re s 100 to 288 C a t n e u t r a l ph vri.th r e s p e c t to d is s o lv e d oxygen and h ydrogen c o n c e n tr a t io n s, r e s p e c t i v e l y. T hese e q u ilib r iu m p o t e n t i a l s w ere c o n s tr u c te d on th e b a s is o f C o b b le 's therm odynam ic c a lc u la tio n s ^ ^ ^ ^ T h e d e t a i l s o f th e c a l c u la tio n a r e d e s c rib e d i n A ppendix A, Below 10 ppb o f d is s o lv e d oxygen th e p o t e n t i a l s o f th e s e a l lo y s g e n e r a lly f a l l dovm to th e p o t e n t i a l re g io n o f hydrogen e le c tro d e. T his shows th a t below 10 ppb o$ oxygen conc e n tr a ti o n r e d u c tio n r e a c tio n may be d o m in an tly hydrogen e v o lu tio n r e a c t i o n. A n o th er im p o r ta n t o b s e r v a tio n i s th a t e x p e rim e n ta l v a lu e s a r e alw ays ab o u t 100 to 500 lo w er th a n th e therm odynam ic p o t e n t i a l o f oxygen e le c tr o d e a t oxygen c o n c e n tr a tio n s above 1 ppm. T h is d if f e re n c e was s m a lle r a t h ig h e r te m p e ra tu re s and g r e a t e r a t lo w er oxygen c o n c e n tr a t io n s. M oreover, th e s lo p e o f p o t e n t i a l w. r. t, lo g a r ith m ic s c a le o f oxygen- c o n c e n tr a tio n i s n o t E T /4F, w hich i s th e t h e o r e t i c a l s lo p e o f r e v e r s i b l e oxygen e le c tr o d e. T hese r e s u l t s can be r a t i o n a l i s e d on th e b a s is o f th e m ixed p o t e n t i a l c o n c e p t. S in c e s o lu ti o n i s h ig h p u r i t y w a te r, a n o d ic r e a c tio n i s m a in ly m e ta l o x id a tio n ( e i t h e r m e ta l d is s o lu t i o n o r o x id e fo rm a tio n o f m e ta l), w h ile c a th o d ic r e a c t i o n i s e i t h e r r e d u c tio n r e a c tio n o f oxygen o r h ydrogen e v o lu tio n r e a c t i o n, d ependin g on t h e ra n g e o f oxygen c o n c e n tr a tio n, (F ig u re s 81 to 8 5 ).

50 3'i S t a b i l i t y o f m e ta l o x id e v ;, r. t. d is s o lv e d oxygen c o n c e n tr a tio n a t v a r io u s te m p e ra tu re s i s shown i n F ig u re 2$. As e x p e c te d, Ni h as h ig h e s t and Cr h as lo w e s t v a lu e s o f oxygen c o n c e n tr a tio n f o r e q u ilib riu m c o e x is te n c e o f m e ta ls and t h e i r o x id e s. Fe i s in te r m e d ia te betw een th e s e two m e ta ls. In a l l c a s e s e q u ilib r iu m d i s s o l ved oxygen c o n c e n tr a tio n in c r e a s e d w ith an in c r e a s e i n te m p e ra tu re. On th e b a s is o f t h i s s t a b i l i t y diagram, p r a c t i c a l l y, a l l th r e e m e ta ls a r e p a s s iv a t e d i n h ig h te m p e ra tu re w a te r a t any c o n c e n tr a tio n s o f d is s o lv e d oxygen. D e ta ils o f therm odynam ic c a l c u l a t i o n s f o r t h i s diagram a re l i s t e d i n A ppendix. C om parison o f c o r r o s io n p o t e n t i a l v;ith p o te n tia l- p H d iagram s o f F e-n i-c r a l lo y s a t te m p e ra tu re s 100 to 288 C (F ig u re s 1-5) a ls o i n d i c a t e s t h a t a l l F e-n i-c r a l lo y s a re therm o d y n a m ic a lly p a s s iv a t e d i n h ig h te m p e ra tu re n e u t r a l w a te r, b u t Ni may be d is s o lv e d below a b o u t 20 ppb o f oxygen b e c a u se o f " th e p o s s i b le fo rm a tio n o f n ic k e l io n a t n e u t r a l ph. The sudden in c r e a s e in c o r r o s io n p o t e n t i a l o f Ni a t oxygen concent r a t i o n s ppb may be a s s o c ia te d w ith th e a c tiv e to p a s s iv e t r a n s i t i o n o f t h i s m e ta l i n h ig h te m p e ra tu re n e u t r a l w a te r A M ath e m atical E x p re ssio n o f th e C o rro s io n P o t e n t i a l s o f F e-n i-c r A llo y s in te rm s o f Oxygen C o n c e n tra tio n s F or F e-n i-c r a l l o y s, su ch a s Type 504 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800, a l e a s t s q u a re s f i t e q u a tio n f o r e x p r e s s in g th e c o r r o s io n p o t e n t i a l s o f th e a l lo y s i n te rras o f th e d is s o lv e d oxygen c o n c e n tr a tio n s was c o n s tr u c te d i n th e fo llo w in g g e n e ra l.fo rm o f e q u a tio n s.

51 32 = A + B log(cq^ppb) + M) wners a, rs, ana w a re co n sran cs. The c o n s ta n ts, A, B and M f o r th e a l lo y s a t v a rio u s tem p, were c a lc u la te d by co m p u ter. The r e s u l t s a r e shown i n T a b le 2. The c o r r o s io n p o t e n t i a l s by th e above e q u a tio n, i n m ost c a s e s, a g re e w ith th e e x p e rim e n ta l v a lu e s w ith in ±30 mv, T a b le 2. The V alues o f A, B and M f o r Type 3 0 4, In c o n e l 6OO and In c o lo y 800 M a te r ia l T e m p eratu re * * a p p l ic a b l e f o r 0^ 10 to 10,000 ppb O th e rs a r e a p p lic a b le f o r 0^ 1 to 10,000 ppb.

52 3.3.3 S i g n if i c a n t O b s e rv a tio n s 33 D e te c tio n o f H ydrogen P e ro x id e : Two a tte m p ts o f hydro g en p e ro x id e m easurem ents a t open c i r c u i t p o t e n t i a l i n o x y g e n a te d w a te r a t 250 C v/ere made. D is so lv e d oxygen c o n c e n tr a tio n s w ere n e a r 8 ppm. C h em etrics t e s t I t i t, Model H P-10, was u s e d f o r th e a n a l y s i s, ppb o f p e ro x id e v/as d e te c te d i n b o th a tte m p ts. S in c e th e e x p 't a l sy stem was r e f r e s h e d a u to c la v e sy stem, much h ig h e r cone, o f h y drogen p e ro x id e on th e s u r f a c e o f m e ta l e l e c tr o d e was e x p e c te d. I t i s a w e ll known f a c t t h a t h y drogen p e ro x id e i s a r e a c t i o n in te r m e d ia te i n th e oxygen r e d u c tio n p ro c e s s and was a ls o d e te c te d i n th e e x p e rim e n ts. The h y d ro g e n -p e ro x id e d e te c te d may s i g n i f i c a n t l y a f f e c t th e c o r r o s io n p o t e n t i a l s o f th e s e a l lo y s and p o s s i b ly th e s t r e s s c o r r o s io n b e h a v io r o f th e a l lo y s i n h ig h te m p e r a tu r e o x y g en a ted v /a te r. Oxygen Consumption in th e System : The h ig h p r e s s u r e p a r t o f th e e x p e rim e n ta l system was c o n s tr u c te d o f In c o n e l 600, G e n e ra lly, In c o n e l 600 i s l e s s s u s c e p tib le to SCO th an Type jo ^, But unexpected oxygen consu m p tio n by th e w a lls o f p r e h e a te r and a u to c la v e was o b s e rv e d. F ig u re 26 and 27 show th e e f f e c t o f d is s o lv e d oxygen on th e c o r r o s io n p o t e n t i a l o f Type 304 a t 250 C and 288 G, r e s p e c t i v e ly, The i n l e t c o n c e n tr a tio n o f oxygen i n th e f ig u r e s r e p r e s e n ts th e c o n c e n tr a tio n o f oxygen i n fe e d ta n k. As e v id e n t i n th e f ig u r e s, th e d if f e r e n c e betw een i n l e t and o u t l e t conc e n tr a ti o n s a t 288 C i s g r e a t e r th a n t h a t a t 250 C, At 250 C, o r below t h i s te m p e r a tu r e, s in c e oxygen c o n c e n tr a tio n a f t e r p r e h e a te r ( a c t u a l i n l e t Og cone, o f a u to c la v e ) i s c lo s e to t h a t a t e x i t, m ost o f oxygen i s b e lie v e d to be consum ed i n p r e h e a te r. On th e o th e r hand oxygen consum ption i n th e a u to c la v e was a ls o s i g n i f i c a n t a t 288 C, The d if f e r e n c e a t h ig h O2 a p p e a rs l e s s s i g n i f i c a n t p a r t l y due to th e lo g a r ith m ic

53 3k s c a l e f o r O2, an d p a r t l y due to th e consum ption re a c h in g a l i m i t i n g v a lu e. The oxygen cone, i n s id e th e a u to c la v e f o r any c a s e s l i e s somewhere betw een th e cone, a f t e r p r e h e a te r and o u t l e t c o n c e n tr a tio n, 3, 5,4 C om parison o f P re s e n t S tu d y w ith t h a t R ep o rte d i n L i t e r a t u r e P re v io u s w orks done by Sykesand G en eral E l e c t r i c a re reproduced in F igu re 28, G,E. stud y m easured th e c o rro s io n p o t e n t i a l o f Type 304 a t 274 C; one w ith p r e h e a te r p r e s e n t i n th e flo w in g system and n e x t w ith o u t th e p r e h e a te r. B oth r e s u l t s a r e p l o t t e d i n th e F ig u r e. Sykes m easured th e c o r r o s io n p o t e n t i a l o f Type 304 i n o x y g en a ted w a te r a t 230 C. B oth o f th e s e tvra s tu d ie s v;ere made i n r e f r e s h e d a u to c la v e s y ste m s. T hese d a ta a re p l o t t e d on th e b a s is o f i n l e t oxygen, A sudden jump o f c o r r o s io n p o t e n t i a l n e a r 100 ppb o f oxygen was o b s e rv e d f o r a l l c a s e s. Com parison o f p r e s e n t s tu d y w ith th e s e two w orks on th e b a s is o f i n l e t oxygen shows r e a s o n a b ly good a g re e m e n t. Most com parable work w ith p r e s e n t s tu d y was made by In d ig and M cllree^^^^and th e r e s u l t s a r e shown i n F ig u re 29. To m inim ize th e consum ption o f oxygen i n th e sy stem th e y u s e d tita n iu m a u to c la v e. C o rro s io n p o t e n t i a l s o f Type 304 were m easured in oxygenated w ater a t 2?4 C. The r e s u l t s o f t h i s work and t h e i r work a g re e w e ll a t oxygen c o n c e n tr a tio n s above 20 ppb, b u t below 20 ppb oxygen th e p r e s e n t work showed mv h ig h e r v a lu e s.

54 35 3.&. - Summary o f E x p e rim e n ta l E e s u lto 1 ) In a l l c a s e s th e c o r r o s io n p o t e n t i a l in c re a s e d, w ith an in c r e a s e i n oxygen c o n c e n tr a tio n, 2) The e f f e c t o f te m p e ra tu re v/as to s h i f t th e c o r r o s io n p o t e n t i a l o f th e a l lo y s to w ard s th e a c tiv e s id e 3) The p o t e n t i a l. o f P t was alw ays h ig h e r th a n t h a t o f o th e r s a t a l l te m p e ra tu re s and oxygen c o n c e n tr a t io n s. The lo w e st p o t e n t i a l was f o r Cr i n m ost in s ta n c e s. The p o t e n t i a l s o f o th e r allo.ys were between th a t of Pt and Cr. h) A sig m o id a l t r a n s i t i o n o f c o r r o s io n p o t e n t i a l w ith r e s p e c t to d is s o lv e d oxygen c o n c e n tr a tio n was n o te d f o r h i a t a l l te m p e ra tu re s. T h is b e h a v io r may bo a s s o c ia te d w ith th e a c tiv e to p a s s iv e t r a n s i t i o n o f an o d ic k i n e t i c s o f t h i s m e ta l in h ig h te m p e ra tu re w ate r 5) For p r a c t i c a l p u rp o se th e c o r r o s io n p o t e n t i a l o f P t, N i, Type 304 s t a i n l e s s s t e e l, I n c o n e l-600 and In c o lo y 800 can bo c o n s id e re d r e v e r s i b l e in th e te m p e ra tu re and oxygen c o n c e n tr a tio n ra n g e s s tu d ie d in t h i s i n v e s t i g a t i o n. 6 ) Thermodynamic c a l c u l a t i o n s show t h a t P e-n i-c r a l lo y s a r e p a s s iv a t e d a t a l l c o n c e n tr a tio n s o f d is s o lv e d oxygen in high tem p eratu re w ater. 7) C o rro sio n p o t e n t i a l s o f th e a l lo y s i n o x y g enated h ig h te m p e ra tu re w ate r fo llo w e d m ixed p o t e n t i a l th e o r y. The a n o d ic r e a c tio n was m e ta l o x id a tio n and oxygen r e d u c tio n and h ydrogen e v o lu tio n r e a c tio n s v/ere th e c a th o d ic r e a c t i o n s.

55 Figure 6. Experimental setup for oxygen 1. D is tille d V /ater 2. T ra n s f e r Pump 3. W ater P u r i f i c a t i o n S ystem, M illip o r e Zf. C o n d u c tiv ity M eter 5. S torag e Tank 6. Oxygen C on tro l Tank 7. Feed Tank 8. M icro Pump 9. Beckman Oxygen A nalyzer 10. Gas P r o p o r tio n e r 11. High P re ssu re Pump 12. P r e h e a te r 13. A utoclave 14. P ressu re Gauge 15. A fte r-c o o le r 16. Back P r e s s u r e R e g u la to r 17. H oldup Tank 18. D rain 36

56 @ JV ^0

57 38 F ig u re 7, Working e le c tr o d e a s s e m b ly.- From l e f t F i r s t : A ssem bly o f specim en w ith T e flo n c o a te d specim en h o ld e r and Conax h ig h p r e s s u r e f i t t i n g S econd: E xploded view o f th e f i r s t T h ird : A ssem bly o f m e ta l ro d e l e c tr o d e v â th Conax h ig h p r e s s u r e f i t t i n g F ourth : Exploded view o f th e th ir d

58 Type 301f v/ith T eflon co ated specim en h o ld e r H 100 Type 30k m e ta l ro d e l e c tr o d e T e m p eratu re : 288 C ü-100 I n l e t O2 C one.: 6.4 PPm Time, hours F ig u re 8. C o rro s io n p o t e n t i a l s o f Type 304 v e rs u s tim e ; e f f e c t o f e le c tr o d e c o n f ig u r a tio n s

59 Type 304 w ith T e f lo n c o a te d specim en h o ld e r g 400 Type 304 m e ta l ro d e le c tr o d e t T em perature: loo^c I n l e t H2O2 Cone. : 10 ppm 100 T i m e, h o u r s F ig u re 9, C o rro s io n p o t e n t i a l s o f Type 304 v e rs u s tim e ; e f f e c t o f e le c tr o d e c o n f ig u r a tio n s

60 1 0 0 f o CL c o -200 PVofer Qualify Temperature C Og In : 240 ppb - OgOut- 180 ppb ph In :6.4 ph Ouf:6.2 o Heating F ig u re 10, Time, Hours C orrosion p o te n tia ls v ersu s tim e a t 288 C 30 40

61 400 P t,300 -P T e m p eratu re: 250 C O2 In : 8 ppm Og Out ppm ph In : 6,6 ph O ut: 6.8 Cr 600 N-i g Tim e, h o u rs F ig ure 11. C orrosion p o te n tia ls v ersus tim e a t 250 C

62 > Ë 800r LEGEND o A I50 C A 200 C 250 C 288 C X. Platinum ' ^150 C... A - - '" ' A A--' / A " ' 200 C - - t a 250«c lo œ c / " _ X ^x 288«c >sr 14: ÿ / -600L ,000 Dissolved Oxygen Concentration, ppb Figure 12, Corrosion potentials of Pt versus dissolved oxygen 10,000

63 600 r LEGEND o A 150 C A 200 C C C /C N ickel CL h 100 / / / ; / C x '^ r a 288 C J _ il_ ,000 10,000 Dissolved Oxygen Concenlrolion, ppb Figure 13. Corrosion potentials of Ni versus dissolved oxygen

64 X 200k E LEGEND o 100 C A I50 C A 200 C e 250 C Chromium 2 ^ 1 0. "., o / C A cr" -600 = ,000 Dissolved Oxygen Concentration, ppb Figure 14. Corrosion potentials of Or versus dissolved oxygen 10,000

65 600 > E 200 o I0 0 c A I50 C A 200 C e 2 50 C 288 C '^'pe Stainless Steel 0 V ' 200 C K 288 C 1^^250=0 / H-cT - V L ,000 Dissolved Oxygen Concentration, ppb Figure 15. Corrosion potentials of Type 304 versus dissolved oxygen K^OOO

66 400 LEGEND O lo Π^ Inconel A 150 C A 200 C o 250 C 288 C O ^ / /l5 0 C b sr b ^ ". ^ /' 288 C u -400 A J _ J _ xl I ,000 10,000 Dissolved Oxygen Concentration, ppb Figure 16. Corrosion potentials of Inconel 600 versus dissolved oxygen

67 LEGEND IOO C I50 C 200 C 250 C 288 C Incoloy ' ' 200 } to o 1,000 Dissolved Oxygen Concentration, ppb 10,000 F ig u re I 7, C o rro s io n p o t e n t i a l s o f In c o lo y 800 v e rs u s d is s o lv e d oxygen

68 600 r O2/H 2O > 200 h -200 Oh Q Platinum o Type A-- Inconel " O Incoloy a -- Nickel - A-- Chromium Temperature ' 2 50 C o -400 h H /Hg ( I ppb) - (Ippm) L Dissolved Oxygen Concentration, ppb F igure 18, C orrosion p o te n tia ls v ersu s d isso lv e d oxygen a t 2$0 C

69 Inlet Oxygen- 5 ppb Outlet Oxygen- ^ 5ppb -200 o H I50«C HH250 ck Heating I50 C-H Tim e, Hours F ig u re 19. The e f f e c t o f te m p e ra tu re change on th e c o r r o s io n p o t e n t i a l s i n d e a e ra te d w a te r

70 Inlet Oxygen- 6.7ppm Outlet Oxygen- ^ 6.4ppm o 300 g 2 œ H Heating h250 C-H k - l 7 5 C-H -200, T im e, Hours Figure 20. The effect of temperature change on the corrosion potentials in oxygenated water

71 Temperaiurë- i5g -C 400 Ogin loppb 02ln:2,2l00ppb OgOut: 3ppb I ut-'2,ll8 0 ppb Ogln-' 10ppb 020ut*5ppb 300 > ûo Heating nz Tim e, Hours Figure 21. The effect of oxygen concentration change on the corrosion potentials at 1$0 C

72 Température:2 50 C o -200 C L o \ Heating Tim e, Hours Figure 22, The effect of oxygen concentration change on the corrosion potentials at 250 C

73 Equilibrium Potential ot Neutral ph,mv.

74 -300 Æ o ^ '!0' 10' Dissolved Hydrogen Concentration, ppb F ig u re 24, E q u ilib riu m p o t e n t i a l s o f hydrogen e le c tr o d e

75 1 0 - ^ _ rlq -50 ulo 1-60 oio 70 - ;^ io-8o _ 10' ^ T em perature, C F ig u re 25- E q u ilife riu m c o n c e n tr a tio n s o f oxygen v e rs u s te m p e ra tu re f o r th e o x id a tio n o f F e, Ni-,and Gr,,

76 M a te r ia l: Type 304 S t a i n l e s s S te e l T em perature: 2^0 C, I n l e t Oxygen Oxygen a f t e r P r e h e a te r O u tle t Oxygen Q O ^ O' o O ' O' o o ,000 10,0: D isso lv e d Oxygen, ppb F ig u re 26, C o rro s io n p o t e n t i a l s v e rs u s d is s o lv e d oxygen a t 250 G; th e e f f e c t o f oxygen consum ption in th e system

77 ^ M a te r ia l: Type 304 S t a i n l e s s Tem perature: 288 C s t e e l y I n l e t Oxygen e Oxygen a f t e r P re h e a te r J ' -200 # O u tle t Oxygen / ,0 0 0 D issolved Oxygen, ppb F ig u re 27. C o rro s io n p o t e n t i a l s v e rs u s d is s o lv e d oxygen a t 288'^C; th e e f f e c t o f oxygen consum ption in th e system

78 TTT TT] 1 I I n llt j " T TTi Type 304 s t a i n l e s s s t e e l GE (v /ith o u t p r e h e a te r ) a t 274 C ^ J. F. Sykes a t 250 C -600 GE (w ith p r e h e a te r ) a t 274 C L I I I I I I I I I I I I I I I I I I! 1 l_u-l.l..l I n l e t C o n c e n tra tio n o f D is so lv e d O xygen, ppb F ig u re 28. C o rro s io n p o t e n t i a l s v e rs u s d is s o lv e d oxygen c o n c e n tr a tio n 10,000

79 :60, mvh OtoiO,OOOppb RETURN FROM 10,000_,H RUN L A,A RUN M i-i in ,000 02PPb(Input anda O utput s anda. ) 10., 000 F ig u re 29. E f f e c t o f d is s o lv e d oxygen c o n c e n tr a tio n on th e c o r r o s io n p o t e n t i a l o f Type 3 0k s t a i n l e s s s t e e l a t 274 C ( a f t e r In d ig and M c llre c ^ ^ ^ ^ )

80 61 Silver Rod, 3 mm D ia. Conax Fitting Stainless Steel Gland Teflon Insert Stainless Steel Coupling Electrode Chamber, 6mmX3mm T eflo n Tubing Chloridized Silver Rod Buffer Compartment, 9mmX6mm T eflon Tubing Zirconia Sand Soaked in 0.01 N KCI Porous Zirconia Plug Teflon Stop End Zirconia Sand Soaked in Test Solution -Luggin Capillary, Zirconia Tubing F ig u re 3 0. S chem atic diagram o f Ag/AgCl r e f e r e n c e e le c tr o d e

81 /ig u r B.3 1. Ag/AgCl r e f e r e n c e e l e c tr o d e 62

82 63 0 ; C a lc u la te d I : E x p e rim e n ta l F ig u re 32, C a lc u la te d and e x p e rim e n ta l s ta n d a rd e le c tr o d e p o t e n t i a l s o f A g /lgc l e le c tr o d e w. r. t, s ta n d a r d hydrogen e le c tr o d e a t e le v a te d te m p e ra tu re, ( a f t e r H ef. 16)

83 E =2.3755x10' xlO'\ x 1 0 ^ 1 2 E = E - - ^. P n a c,., ac,_ =o.oiivi #0 ^ C F ig u re 33. E le c tro d e P o t e n t i a l o f Ag/AgCl R e fe re n c e E le c tro d e

84 ft. CORROSION POTENTIAL OF IRON-NICKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE WATER; THE EFFECT OF HYDROGEN PEROXIDE 4.1 I n tr o d u c tio n H ydrogen p e ro x id e i s o f te n d e te c te d when a m e ta l e le c tr o d e i s im m ersed i n t o aqueous s o lu tio n s c o n ta in in g d is s o lv e d oxygen o r form ed a s an in te r m e d ia te com plex when oxygen i s c a th o d ic a lly re d u c e d. D uring BWR p la n t s t a r t u p and shutdow n t r a n s i e n t s, i t h a s been d e te rm in e d t h a t in c r e a s e d q u a n t i t i e s o f hydro g en p e ro x id e and oxygen a re p r e s e n t ^ S i n e e hydro g en p e ro x id e i s o f te n d e te c te d i n BWR th e o b e rv e d c o r r o s io n phenom ena o f F e-n i-c r a llo y s i n BWR en v iro n m en t c o u ld be in f lu e n c e d s i g n i f i c a n t l y by t h i s s u b s ta n c e. % T h is s tu d y i n v e s t i g a t e d th e e f f e c t o f d is s o lv e d hydrogen p e ro x id e c o n c e n tr a tio n on c o r r o s io n p o t e n t i a l s o f Type 304 s t a i n l e s s s t e e l, In c o n e l 600, In c o lo y 800 and platin um a t te m p eratu res C. 4.2 Theory of Hydrogen P eroxide H ydrogen p e ro x id e can a c t a s an o x id iz in g o r a re d u c in g s u b s ta n c e. The o x id a tio n o f h y drogen p e ro x id e i s, ( a c id ) ( n e u t r a l o r weak a l k a l i ) 65

85 66 and th e e le c tr o d e p o t e n t i a l i s g iv e n by Eg - ^ 1. 5 E i s 0.62V a t 100 C and 0.44V a t 288 C. The re d u c tio n o f h y ro g en p e ro x id e p ro c e e d s by th e r e a c tio n, HgOg + 2H'*' + 2e = 2H^0 ( a c id ) ^2^2 ^2e= 20H" ( n e u t r a l o r weak a l k a l i ) w ith th e e l e c tr o d e p o t e n t i a l E i s 1.71V a t 100 C and 1.61V a t 288 C The e q u ilib riu m p o t e n t i a l s o f th e s e r e a c tio n s in h ig h te m p e ra tu re n e u t r a l s o lu tio n s a r e shown i n F ig u re s 35 and 36, r e s p e c t i v e l y. H e n ry 's law was a p p lie d f o r r e p la c in g p a r t i a l p r e s s u r e o f oxygen w ith d is s o lv e d c o n c e n tr a tio n. C o b b le 's therm odynam ic c a l c u l a t i o n s w e r e a d o p te d f o r th e c o n s tr u c tio n o f th e d iagram and d e t a i l s a re d e s c rib e d i n A ppendix A. S in c e p o t e n t i a l fo r th e o x id a tio n r e a c tio n o f hydrogen p e ro x id e i s a f u n c tio n o f th e c o n c e n tra tio n r a t i o o f d is s o lv e d oxygen to h y d ro g en p e ro x id e, th e e q u ilib r iu m p o t e n t i a l s f o r th e r e a c t i o n w ere p l o t t e d a g a in s t Cq /Cj^ q, The s ta n d a r d p o t e n t i a l s fo r th e r e a c tio n, r e d u c tio n r e a c t i o n, E qq= 1,71V o r ^ " ^.6 1 V, cannot be o b ta in e d e x p e rim e n ta lly in aqueous s o lu ti o n s, due to v ig o ro u s oxygen e v o lu tio n a t t h a t p o t e n t i a l. Above e q u a tio n s in d i c a t e t h a t 2.303R T /F V change p e r ph and 2.303R T /2F V change p e r decade change in a^ ^ a re e x p e c te d. At room te m p e ra tu re e a r l y w o rk ers d em o n strates, th a t, w h ile th e 59 mv change p e r ph was v e r i f i e d e x p e rim e n ta lly on h ig h s u r f a c e a r e a e le c tr o d e, th e r e q u ir e d mv change p er decade change in a n was n o t observed^^^^. ^2^2

86 67 th e e le c tr o d e m orphology, i t s p re tre a tm e n t and m a te r i a l, on e l e c t r o l t e s t i r r i n g and on th e p re s e n c e o f oxygen i n th e s o lu ti o n. T hese c h a r a c t e r i s t i c s e s t a b l i s h th e p o t e n t i a l o f a HgOg e l e c tr o d e a s a m ixed p o te n tia l^ ^ ^ ^ S in c e r e d u c tio n p o t e n t i a l o f hydro g en p e ro x id e i s more p o s i t i v e th a n o x id a tio n p o t e n t i a l a t th e te m p e ra tu re s in v e s t i g a t e d h y drogen p e ro x id e can be decom posed s p o n ta n e o u sly b o th hom ogeneously and h e t e r o g e n e o u sly. Homogeneous d e c o m p o sitio n i s c a ta ly z e d by a number o f m e ta l io n s, i n p s j r t i c u l a r, th o s e o f th e t r a n s i t i o n m e ta ls and by c e r t a i n enzym es. H ete ro g e n eo u s d e c o m p o sitio n i s c a ta ly z e d by m ost s u r f a c e s, i n p a r t i c u l a r, m e ta ls, m e ta l o x id e s, m e ta l h y d ro x id e s and v a r io u s c a rb o n s. E s p e c ia lly c a t a l y t i c a l l y a c tiv e a r e th e p la tin u m m e t a l s i ^ The an o d ic r e a c tio n o c c u rs a t p o t e n t i a l s E E^, w here E^ i s th e e le c tr o d e p o t e n t i a l o f th e r e a c t i o n, w hereas th e c a th o d ie p a r t o f th e r e a c t i o n o c c u rs a t p o t e n t i a l s E E^, w here E^ i s th e p o t e n t i a l o f th e H^O^/H^O. The n e t r e a c t i o n, r e s u l t i n g from th e sum m ation o f th e a n o d ic and c a th o d ic p a r t r e a c t i o n s, i s EHgOg =02+ ah^o th a t i s, hydrogen p e ro x id e i s decom posed a t th e r e s t p o t e n t i a l by an e le c tro c h e m ic a l m echanism to y i e l d oxygen and w a te r, lilfhile e le c tro c h e m ic a l m echanism f o r h ydrogen p e ro x id e d ecom p o sitio n i s p red o m in an t i n n e u t r a l and a c id s o l u t i o n s, a c e r t a i n d eg ree o f c h e m ical d e c o m p o sitio n ta k e s p la c e s im u lta n e o u s ly a t h ig h

87 if,3 E xperim ental if.3,1 Experimental Setup and Procedures The e x p e rim e n ta l s e tu p, shown i n F ig u re 34, was b a s ic a l^ ly same a s t h a t f o r oxygen, d e s c r ib e d i n s e c tio n 3,3, A s l i g h t m o d ific a tio n was made i n th e w a te r fe e d t r a i n f o r m easurem ents w ith th e hydrogen p e r o x id e. The h ydrogen p e ro x id e was added from t h e i r c o n ta in e r to th e fe e d ta n k v /ith a p r e c i s io n m e te rin g pump, Beckman Model 743. The c o n c e n tr a tio n o f hydrogen p e ro x id e was m a in ta in e d i n th e fe e d ta n k a t a d e s ir e d v a lu e by a p ro p e r p r o p o r tio n in g o f th e w a te r and ch e m ical fe e d r a te s. The feed w ater was d ea erate d w ith argon. The w a te r from th e fe e d ta n k and th e e x i t w a te r from th e a u to c la v e w ere p e r i o d i c a l l y a n a ly z e d. Due to r a p i d d ec o m p o sitio n r a t e o f hydrogen p e ro x id e, p r e h e a te r was n o t u s e d. T em p eratu re i n s i d e th e a u to c la v e was c o n t r o lle d by a th erm o co u p le p la c e d on th e same l e v e l o f w orking e l e c tr o d e to m inim ize th e e f f e c t o f th e rm a l zo n e. W orking e le c tr o d e s w ere m e ta l ro d e l e c tr o d e s (s e e F ig u re 7 ). Specim en p r e p a r a tio n, m easurem ent and r e f e r e n c e e le c tr o d e a r e d e s c r ib e d i n s e c t io n C hem ical A n a ly s is F o r a n a ly s is o f hydrogen p e ro x id e C h em etrics t e s t k i t, Model HP-10, was u s e d. The t e s t k i t c o n s is ts o f c o lo r c o m p arato rs and t e s t am poules w hich c o n ta in s ammonium th io c y a n a te and f e r r o u s i r o n i n a c id s o lu ti o n. The t e s t i s b a sed on th e o x id a tio n o f ir o n by p e ro x id e and th e fo rm a tio n o f th e i n t e n s e ly c o lo re d f e r r i c t h i o -

88 69 c y a n a te com plex (re d -o ra n g e color)the lo w e s t conc. o f hydrogen p e ro x id e d e t e c ta b le vri.th t h i s m ethod i s ab o u t 50 ppb. D is so lv e d oxygen was a l s o a n a ly z e d a lo n g w ith h ydrogen p e ro x id e m easurem ents. C h em etrics d is s o lv e d oxygen t e s t k i t was u sed f o r oxygen a n a ly s is. The t e s t k i t em ploys c o lo r d e v e lo p in g r e a g e n t, E hodazine D, w hich i s p a le y ello v / i n re d u c e d form, b u t r e a c t s w ith oxygen to p ro d u ce a r e d d i s h - v i o l e t s o l u t i o n ^ I n t e r f e r e n c e o f hydrogen p e ro x id e on oxygen a n a ly s is was a ls o exam ined w ith two c o n c e n tr a tio n s o f hydrogen p e ro x id e, 0,2 ppm and 1 ppm. A f te r d e a e ra tio n o f w a te r w ith a rg o n, oxygen was a n a ly z e d w ith C h em e tric s, Then, h y drogen p e ro x id e was added i n th e same w a te r and m easured th e oxygen c o n c e n tr a tio n a g a in. At 0,2 ppm hydrogen p e ro x id e no d if f e re n c e in oxygen c o n c e n tr a tio n was o b s e rv e d, b u t w ith 1 ppm hydrogen p e ro x id e th e re a d in g o f oxygen was in c r e a s e d from 10 ppb to 50 ppb. T h is h ig h e r r e a d i n g - in oxygen may be due to e i t h e r d ec o m p o sitio n o f h ydrogen p e ro x id e i n t o oxygen and w a te r o r in t e r f e r e n c e o f hydrogen p e ro x id e w ith th e oxygen a n a ly s is. I n any c a se i n th e p re s e n c e o f 1 ppm p e ro x id e i n v /a te r, th e oxygen c o n c e n tr a tio n i s l e s s th a n 50 ppb. * Tradem ark, C hem etrics, In c,

89 4.4 Results 70 ; T e s t m a trix f o r hydro g en p e ro x id e, a lo n g w ith some p e r t i n e n t d a ta, i s g iv e n in T a b le 2. C o rro s io n p o t e n t i a l s o f P t, Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800 w ere m easured i n th e s e t e s t s. The c o n c e n tr a tio n o f h y d rogen p e ro x id e i n th e o u t l e t s tre a m was n e a rly ze ro ( u n d e te c ta b le by th e a n a l y t i c a l te c h n iq u e u se d ) a t a l l te m p eratu res above 100 C because o f th e ra p id decom position. At 100 C th e o u t l e t h ydrogen p e ro x id e c o n c e n tr a tio n was a p p ro x im a te ly one h a l f o f th e fe e d c o n c e n tr a tio n. The chem ica l a n a ly s is o f d is s o lv e d oxygen and h y d rogen p e ro x id e i n th e i n l e t and th e o u t l e t s tre a m s gave r e s u l t s w hich s a t i s f i e d th e m ass b a la n c e f o r oxygen from th e r e a c t i o n. ph's o f i n l e t and o u t l e t w a te r w ere a ls o m easured a t room te m p e ra tu re, B oth v a lu e s w ere n e a r ly same and w ere c lo s e to n e u t r a l ph, F ig u re s 37 and 38 show ty p i c a l re s p o n s e s o f th e c o r r o s io n p o t e n t i a l w ith tim e. I n i t i a l s te a d y s t a t e was re a c h e d i n ab o u t 15 to 20 h o u rs, b u t s te p w is e in c r e a s e i n te m p e ra tu re re d u c e th e tim e f o r r e a c h in g th e s te a d y s t a t e to a b o u t 5 h o u rs. T h is im p lie s s i g n i f i c a n t p o r ti o n o f th e tim e f o r s te a d y s t a t e may be s p e n t f o r th e system to re a c h th e s te a d y s t a t e. S in c e F ig u r e s 35 and 36 show th e same v a lu e s o f c o r r o s io n p o t e n t i a l o f th e a l lo y s a t 250 C, i t can be s t a t e d t h a t th e c o r r o s io n p o t e n t i a l o f th e a l lo y s w ere n o t a f f e c te d by th e s te p w is e in c r e a s e

90 in te m p e ra tu r e..the r e s u l t s a t d i f f e r e n t te m p e ra tu re s f o r th e in d i v id u a l m e ta ls a r e shov/n a s a f u n c tio n o f i n l e t hydrogen p e ro x id e c o n c e n tr a tio n i n F ig u re s 39 to it-2. The c o r r o s io n p o t e n t i a l s o f a l l fo u r m e ta ls in c r e a s e d w ith in c r e a s in g hydrogen p e ro x id e c o n c e n tr a tio n.. At 100 C 200 to 250 mv in c r e a s e i n p o t e n t i a l was o b se rv e d fo r 3 decade change i n p e ro x id e c o n c e n tr a tio n. At te m p,. above 200 C i n i t i a l r i s e v/as a b o u t 600 mv v/ith in c r e a s in g p e ro x id e c o n c e n tr a tio n up to 1,000 ppb, th e n n e a rly no change i n p o t e n t i a l was o b s e rv e d above t h i s c o n c e n tr a tio n. The p o t e n t i a l d e c re a s e d v /ith i n c r e a s in g te m p e r a tu re. T h is e f f e c t was g r e a t e s t a t low c o n c e n tr a tio n o f hydrogen p e ro x id e. At 20 ppb o f h y d ro g en p e ro x id e n e a rly 700 mv change i n p o t e n t i a l was o b s e rv e d f o r te m p e ra tu re change from 100 C to 288 C,. w h ereas o n ly 200 to 4OO mv change was observed a t 10,000 ppb o f hydrogen p ero x id e. F ig u re s 43 and 44 show th e e f f e c t o f a l lo y co m p o sitio n s on th e c o r r o s io n p o t e n t i a l a t 100 C and 288 C a lo n g w ith e q u ilib riu m p o t e n t i a l s o f h y d ro g en p e ro x id e s, r e s p e c t iv e l y. S in c e o x id a tio n p o t e n t i a l o f hydro g en p e ro x id e i s a f u n c tio n o f th e c o n c e n tr a tio n r a t i o o f th e e q u ilib riu m p o t e n t i a l s f o r th e r e a c t i o n was shovm on th e f ig u r e w ith v a lu e s o f /C g ^ =10 ^ and 10^, r e s p e c t iv e l y. At 100 G, w h ile c o r r o s io n p o t e n t i a l s a re d is p e r s e d w ith a l lo y s a t th e p e ro x id e c o n c e n tr a tio n s below 900 ppb, a l l m e ta ls show same p o t e n t i a l s above t h i s c o n c e n tr a tio n o f p e r o x id e, c lo s e to th e e q u ilib r iu m p o t e n t i a l o f O2/H 2O2. N o tic e t h a t above 9OO ppb a p p r e c ia b le am ount o f hydrogen p e ro x id e was d e te c te d a t e x i t s i d e. T h is in d i c a t e d th a t

91 th e p o t e n t i a l s d e v e lo p e d i n th e s e c o n c e n tr a tio n ra n g e s o f p e ro x id e m ig h t fo llo w th e e q u ilib r iu m p o t e n t i a l o f ~2/~2p2. In F ig u re Ll± p la tin u m shows th e h ig h e s t v a lu e o f p o t e n t i a l a t a l l c o n c e n tr a tio n s o f hydrogen p e ro x id e and o th e r s have n e a rly same c o r r o s io n p o t e n t i a l. The p o t e n t i a l d if f e r e n c e betw een p la tin u m and o th e r a llo y s are 100 to 200 mv, 72

92 Zf,5 Discussion 73 The d if f e r e n c e i n e q u ilib riu m p o t e n t i a l betv/een o x id a tio n and r e d u c tio n r e a c tio n o f h ydrogen p e ro x id e i s a b o u t 0,6 to 1 V d epending upon th e c o n c e n tr a tio n o f p e ro x id e and te m p e r a tu re. E q u ilib riu m r e d u c tio n p o te n t i a l o f p e ro x id e i s in c r e a s e d w ith in c r e a s in g p e ro x id e and o x id a tio n p o t e n t i a l i s in c r e a s e d vri.th r a t i o. C om parison o f e x p e rim e n ta l d a ta vrlth therm odynam ic e q u ilib r iu m p o t e n t i a l shows t h a t 1) A bove--'100 ppb o f i n l e t hydrogen p e ro x id e c o n c e n tr a tio n e x p e rim e n ta l v a lu e s l i e betw een o x id a tio n and r e d u c tio n p o t e n t i a l s o f p e ro x id e e l e c tr o d e, 2) B elow 'v 100 ppb o f p e ro x id e e x p e rim e n ta l v a lu e s l i e below th e e q u ilib riu m o x id a tio n p o t e n t i a l o f p e ro x id e e l e c tr o d e. The c o n c e n tr a tio n o f hydrogen p e ro x id e fo r t h i s t r a n s i t i o n in c r e a s e d w ith te m p e ra tu re. T h is im p lie s t h a t hydrogen p e ro x id e may no lo n g e r p a r t i c i p a te i n th e developm ent o f p o t e n t i a l o f th e m e t a l s.a t th e c o n c e n tr a tio n s below 100 ppb. Com parison o f th e e x p e rim e n ta l d a ta vri.th th o s e i n o x y g en a ted w a te r (F ig u re s 12-17) a ls o showed th e fo llo v â n g tr e n d s. 1) At 100 C th e c o rro s io n p o t e n t i a l s o f F e-n i-c r a l lo y s i n v /a ter c o n ta in in g p e ro x id e v;ere alw ays h ig h e r th a n t h a t i n o x y g en ated v /a te r, w hereas p la tin u m showed r e v e r s e tr e n d, 2) The c o r r o s io n p o t e n t i a l s f o r hydrogen p e ro x id e w ere c lo s e to th e p o t e n t i a l s in:, o x y g en a ted w a te r a t h ig h e r te m p e ra tu re s ( C ), Com parison o f F ig u re 44 and 45 shows t h i s tr e n d c l e a r l y.

93 74 S in c e most o f c o r r o s io n p o t e n t i a l s do n o t fo llo w t h e o r e t i c a l p o t e n t i a l o f p e ro x id e e l e c tr o d e th e p o t e n t i a l s d ev e lo p ed may fo llo v ; m ixed p o t e n t i a l th e o r y. P o s s ib le a n o d ic r e a c tio n s a r e o x id a tio n o f p e ro x id e to oxygen a n d /o r m e ta l o x id a tio n, w hereas c a th o d ic r e a c tio n s a r e 1) r e d u c tio n o f p e ro x id e to w a te r, 2) r e d u c tio n o f v ;a ter and 3) re d u c tio n o f oxygen form ed by d ecom p o sitio n o f p e ro x id e. B ased on e x p e rim e n ta l o b s e r v a tio n and therm odynam ic c a l c u l a t i o n, fo llo w in g c o n c lu s io n s can be drav/n, 1) At 100 C th e a l lo y s may show e q u ilib r iu m p o t e n t i a l o f r e a c tio n a t p e ro x id e c o n c e n tr a tio n above 900 ppb. 2) At o th e r te m p e ra tu re s and p e ro x id e c o n c e n tr a tio n s m ixed p o t e n t i a l c o n c ep t i s a re a s o n a b le e x p la n a tio n f o r th e sy stem. P la u s ib l e r e a c tio n c o u p le s a re m e ta l o x id a tio n and oxygen re d u c tio n a n d /o r o x id a tio n and r e d u c tio n o f p e ro x id e. At 20 ppb p e ro x id e dom inant c a th o d ic r e a c tio n may be r e d u c tio n o f w a te r.

94 Com parison o f P r e s e n t S tudy w ith t h a t R ep o rted in L i t e r a t u r e Only l i m i t e d vrark h a s been r e p o r t e d i n th e l i t e r a t u r e f o r c o r r o s io n p o t e n t i a l m easurem ent i n hydrogen p e ro x id e s o lu ti o n. The e f f e c t o f h y drogen p e ro x id e a d d i tio n on th e c o r r o s io n p o t e n t i a l o f Type: 304 s t a i n l e s s s t e e l i n a ^ ra t^ g ^ ^ w a te r a t 6 6, 93 and C v/as s tu d ie d by G en eral E l e c t r i c. The d a ta a t 66 C and 93 C a r e shov/n i n F ig u re 4 6. The a d d i tio n o f 10 ppm h ydrogen p e ro x id e in c r e a s e d th e c o r ro s io n p o t e n t i a l o f s t a i n l e s s s te e ]. a p p ro x im a te ly 225 mv and lo w e r th e p o t e n t i a l o f p la tin u m 94 mv. They a ls o found th a t th e e f f e c t o f h y d rogen p e ro x id e a d d i tio n was o n ly li m i t e d f o r a s h o r t p e r io d o f tim e a t 93 C due', to th e r a p i d d ec o m p o s itio n. The e x p e rim e n ta l r e s u l t s a t 274 G a ls o shov/ed same tr e n d s ( s e e T a b le 3 ). The a d d i tio n o f hydrogen p e ro x id e cau se d an in c r e a s e i n c o r r o s io n p o t e n t i a l o f s t a i n l e s s s t e e l, and a d e c re a s e i n th e p o t e n t i a l o f p la tin u m. - T able 3 EFFECT O F H,0, ON THE CORROSION AND OXIDATION POTENTIAL IN SIMULATED BWR WATER* AT 274X (525"F) HjO, Concentration Potential V SHE (ppb) Type-304 SS Pt Inlol walor conlainod 200 ppb O, and 25 ppb H

95 S in c e v ;a te r c h e m is try f o r G.E i s s tu d y was n o t same a s t h a t f o r th e p r e s e n t w ork, d i r e c t com parison o f b o th r e s u l t s i s n o t p o s s i b l e. W hile good ag reem en t v/as o b se rv e d b etw een th e s e two s t u d i e s a t low te m p e r a tu re s, a c e r t a i n d is a g re e m e n t was found v â th th e r e s u l t s a t 274 C. P r e s e n t w ork d id n o t show any d e c re a s e i n p o t e n t i a l o f P t w ith h y d ro g en p e ro x id e a d d i tio n a s was found by G.E. 76 A n o th er co m parable v/ork was made by S y k es, He s tu d ie d th e e f f e c t o f h y d ro g en p e ro x id e on th e c o r r o s io n p o t e n t i a l o f a number o f m e ta ls i n o x y g e n a te d h ig h te m p e ra tu re w a te r. Two c o n c e n tr a tio n s o f h y drogen p e ro x id e v/ere ch o sen f o r th e stu d y, one v /ith 1 ppm and th e o th e r v /ith 10 ppm. H is d a ta f o r Type 304 s t a i n l e s s s t e e l and In c o n e l 600 a t a r e shown i n F ig u re 47 and 4 8, r e s p e c t i v e l y. F or 10 ppm h y d ro g en p e ro x id e Sykes d a ta and p r e s e n t work show good a g re e m e n t, b u t a b o u t 2OO-4OO mv lov/er v a lu e was o b s e rv e d v /ith Sykes r e s u l t s th a n p r e s e n t d a ta a t 1 ppm p e r o x id e. T h is d if f e r e n c e may be due to th e consum ption o f p e ro x id e i n p r e h e a te r f o r S y k es' s tu d y b e c a u se he em ployed p r e h e a te r f o r th e in v e s t i g a t i o n.

96 77 F ig u re E x p e rim e n ta l s e tu p f o r h ydrogen p e ro x id e, n i t r a t e and ch ro m âte 1. D is tille d ivater 2. T r a n s f e r Pump 3. W ater P u r i f i c a t i o n S ystem, t- iillip o r e if. C o n d u c tiv ity M eter 5. S to ra g e Tank 6. D e a e ra tio n Tank 7. M ixing Tank 8. C hem ical M ete rin g Pump 9. Chem ical S torage Tank 10. M ete rin g Pump 11. High P re ssu re Pump 12. A utoclave 13. A f te r-c o o le r lif. P re ssu re Gauge 15. Back P re s s u r e R e g u la to r 16. D rain

97 7&

98 79 T a J jlc 2 TL GT fîa TR IX FOR {ivduoceu FFROXIDK ::TIIÜY l G ir.peraturc? 2 II^O^ Out 2 0^ Out ppb ppb ppb ppb a t 25 C 20 ~ ~ < , ,0 0 0 < 50 2, '\, vo < ,000 ~ 50 < 50 5, , , ,0 < ,000 'V' 50 < 90 5, , , , ,0 < ,0 0 0 < 50 4,

99 H2 O2 (aq) - O2 (aq) + 2 H '^(aq) + 2e Q- 300 \Qo; 200 CD C o n c.of O2 / Conc. of H2 O2, p p m /p p m F ig u re 35» E q u ilib riu m p o t e n t i a l s o f hydrogen p e ro x id e o x id a tio n r e a c tio n

100 1,200 1,100 f T^ 1,000 2 (oq)+2h (oq)+2e 1B I D issolved Hydrogen Peroxide Concentration,ppb Figure 36. Equilibrium potentials of hydrogen peroxide reduction reaction

101 - - - Pt ! Temperature: 250 C H202ln : 900 ppb Ü2020ut 02ln Û20ut : Mot Detected :<50 ppb phin : 6.5 phout : 6.4. ^ BOp.' ' y / ^ ) - F ig u re 37, T i m e, h o u r s C orrosion p o te n tia ls v ersu s tim e a t 2^0 C 15 ~ 2 0

102 200 C h - 250OC f Temperature: 200 C â H202ln : 800 ppb 304 H2020ut : Not Detected Temperature 250 C 02%n :<50 ppb ^2 2^ 900 ppb - 020ut : 400 ppb H202Ûut Not Detected phin : ln <50 ppb phdut ut 400 ppb phin 5.5 phout F ig u re 38, Time, hours C orrosion P o te n tia ls v ersu s tim e a t 200 C and 250 C

103 Type Stainless Sfeei C C ,000 In let H ydrogen Peroxide C o n cen tratio n, ppb Figure 39. Corrosion potentials of Type 304 stainless steel versus inlet hydrogen peroxide 10,000

104 m - : T Incone! IOO"C!, C C Figure 100 UOOO 10,000 Inlet Hydrogen Peroxide Concentration,ppb Corrosion potentials of Inconel 600 versus inlet hydrogen peroxide &

105 Incoloy X IOO C C C ' L _ L...I..I I I l I I I I ,000 10,000 In let H ydrogen Peroxide e C Concentrât tration ion., ppb F ig u re 41. C o rro s io n p o t e n t i a l s o f In c o lo y 800 v e rs u s i n l e t hydrogen p e ro x id e

106 P latinum C ,000 10,000 In let H ydrogen P ero x id e C on centration, ppb Figure 42. Corrosion potentials of platinum versus inlet hydrogen peroxide

107 1,200 1,000 ^ 600 Tern/j era tu re ' 100 C 400 =!0 o 200 Or LEGEND Platinum Type 304 Inconel 6 00 Incoloy Inlet Dissolved Hydrogen Peroxide Concentration, ppb Figure 43. Corrosion potentials vesus dissolved hydi'ogen peroxide at 100 C

108 f I LEGEND Platinum Type 304 Inconel 600 Incoloy 800 Temperature: 288 C U Inlet Dissolved Hydrogen Peroxide Concentration, ppb Figure 44» Corrosion potentials versus dissolved hydrogen peroxide at 288 C oo

109 /H; = 2 œ -200 LEGEND 0 Platinum O Type 3 04 A Inconel 600 O*" Incoloy Temperature C H /Hg {I ppb) H^/Hgdppm! Dissolved Oxygen Concentration, ppb Figure Corrosion potentials versus dissolved oxygen at 288 C

110 A I'LAIINUM lir- 10,, m AOUr.l.) TO M^KE UP I A I Y ' G6')C (150' F) ("I [ < I _ I I I i J 10 VO 10 '10 ' " ^ 0 T Y I'h 30'1 SIAINLESS STEEL F ig u re 46. E f f e c t o f h y drogen p e ro x id e on c o rro s io n and o x id a tio n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l and p la tin u m in a e r a te d v ;a te r.

111 3 0 4 Stainless Steel 250 C 10 ppm HgO; 10 ppm NjH^ Figure Corrosion p oten tial vs. in le t oxygen lev el for 304 sta in less steel at 25o«c. ( a f t e r r e f. 38)

112 Inconel C 10 ppm HgO; loppm NzH< 0; (ppb) Figure I^Q ' Corrosion p oten tial vs. in le t oxygen lev el for Inconel 600 ( a f t e r r e f. 38)

113 5. CORROSION POTENTIAL OF IRON-NIGKEL-CHROMIUM ALLOYS IN HIGH TEMPERATURE HIGH PRESSURE WATER; THE EFFECT OF HYDRAZINE 5.1 I n tr o d u c tio n F o r h ig h p r e s s u r e b o i l e r s, any re m a in in g d is s o lv e d oxygen i n th e fe e d w a te r com bines q u a n t i t a t i v e l y w ith th e m e ta ls o f th e b o i l e r sy stem, u s u a ll y c a u sin g p i t t i n g o f th e b o i l e r tu b e s and g e n e ra l a t t a c k else w h ere ^^^ ^ H y d razin e and sodium s u l f i t e a r e w id e ly u sed oxygen s c a v e n g e rs f o r b o i l e r w a te r tr e a tm e n t. The r e a c t i o n o f h y d ra z in e and sodium s u l f i t e w ith oxygen a r e, N2H^ + 0 ^ = N^- + ZE^O and Na^SO^ + io g = Na^SO^, r e s p e c t i v e l y. U n lik e s u l f i t e a d d i tio n s no s a l t s ac cu m u la te i n th e t r e a t e d w a te r w ith h y d r a z in e. The s c a v e n g in g o f oxygen w ith h y d ra z in e by above r e a c t i o n i s li m i t e d to an o p e r a tin g ra n g e o f C,^^^^H ence, a d d i tio n o f o r g a n o - m e ta llic compound a s a c a ta ly z e r i s a common p r a c t i c e. Above 275 C th e h y d ra z in e d e c o m p o sitio n r e a c t i o n. 3NgH^ = Ng + ZfNH^ becom es s i g n i f i c a n t l y f a s t and re d u c e s th e e f f e c tiv e n e s s o f oxygen scavenging.^ Due to i t s knov/n re d u c in g pow er h y d ra z in e re d u c e s v a r io u s m e ta l lic io n s, to th e m e ta l lic s t a t e a n d /o r re d u c e s m e ta l o x id e s from t h e i r h ig h e r v a le n c y to lo w er o n e s C68) One o f th e b e n e f i c i a l e f f e c t s w ith h y d ra z in e i s th e s t a b i l i z a t i o n o f m a g n e tite by t h i s m echanism. G e n e ra lly, m a g n e tite i s known to be more p r o t e c t i v e th a n h e m a tite. S in c e aqueous s o lu tio n o f h y d ra z in e i s b a s ic ; i t a ls o 94

114 h e lp s n e u t r a l i z e a c id a t t a c k. In a d d i tio n to above m e n tio n e d b e n e f i c i a l e f f e c t o f h y d ra z in e on c o r r o s io n i n h i b i t i o n h y d ra z in e som etim es re d u c e th e c o r r o s io n r a t e by c o n t r o l l i n g a g g r e s s iv e a n o d ic r e a c t i o n i n a way s i m i l a r to an o d ic inhibitorf^^^ R e c e n tly, in n u c le a r pow er p l a n t, e s p e c i a ll y PWR, s m a ll amount o f h y d ra z in e ( ppb) ^"^^^has been added i n fe e d w a te r o f s e c o n d a ry ( o r steam ) s id e due to i t s i n h i b i t i n g e f f e c t on c o r r o s io n. T h e r e fo re, t h i s s tu d y i n v e s t i g a te d th e e f f e c t o f s m a ll am ounts o f h y d ra z in e in w a te r on th e c o r r o s io n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l, In c o n e l 600, In c o lo y 800, n ic k e l and p la tin u m a t te m p e ra tu re s 1G0-288 C, Theory of H ydrazine H y d razin e i s knovm to be a p o w e rfu l re d u c in g a g e n t, b u t i t can be re d u c e d to form ammonia. O x id a tio n r e a c tio n i s, ^2^4 4OH = Ng + 4H2O + 4s and e le c tr o d e n o t e n t i a l i s g iv e n by 4 + POH - l o s M E i s - 1, 216V a t 100 G and -1,684V a t 288 C. R e d u c tio n r e a c tio n o f h y d ra z in e i s. and e l e c tr o d e p o t e n t i a l can be w r itt e n a s, E i s 0,1 63V a t 100 C and V a t 288 C.

115 9 6 i The e q u ilib riu m p o t e n t i a l s o f th e s e r e a c tio n s i n h ig h te m p e ra tu re n e u t r a l s o lu ti o n s a r e shown in F ig u re s 49 and 50, r e s p e c t i v e l y, S in c e n itr o g e n was u sed f o r d e a e ra tio n o f w a te r f o r t h i s in v e s t i g a t i o n, was assum ed to be 1 a tm o sp h e ric p r e s s u r e. E q u ilib riu m p o t e n t i a l s f o r th e re d u c tio n r e a c tio n o f h y d ra z in e i s a f u n c tio n o f C o b b le 's therm odynam ic c a lc u la tio n s w ere a d o p te d f o r th e c o n s tr u c tio n o f th e diagram and d e t a i l s a r e d e s c rib e d i n A ppendix, Above e q u a tio n s in d i c a t e t h a t 2,303R T /F v o l t change p e r poh and 2.303F T /2 F v o l t change p e r decade change i n a ^ jj a r e e x p e c te d. The p o t e n t i a l d iagram s show h y d ra z in e i s therm odynam ic a l l y u n s ta b le vn.th r e s p e c t to d is p r o p o r tio n a t io n in t o n itr o g e n and ammonia. I t i s th e k i n e t i c b a r r i e r o f b re a k in g th e n it r o g e n - n it r o g e n bond t h a t e n a b le s h y d ra z in e to e x i s t f o r any le n g th o f tim e^^^^ G e n e ra lly, h y d ra z in e s o lu tio n s a r e s t a b l e u n d e r norm al s to r a g e _ c o n d itio n s, i f c o n ta c t w ith a i r, o x id iz in g o r c a t a l y t i c a g e n ts and im p u r itie s i s avoided^^ D ecom position o f h y d ra z in e i s cau se d by e le v a te d te m p e ra tu re s a n d /o r th e p re s e n c e o f c a t a l y t i c s u r f a c e s o r io n im p u ritie s ^ ^ ^ ^ Due to th e a c id d is s o c ia tio n s r e a c t i o n, h y d razin n m -io n i s a s t a b l e s p e c ie in a c id s o lu ti o n s. At room te m p e ra tu re th e boundary betw een th e dom ains o f predom inance fo r i s a t ph 7.99^^*^^

116 Experimental E xperim ental Setup and P rocedures E x p e rim e n ta l s e tu p f o r th e s tu d y was b a s i c a l l y same a s t h a t f o r h y d ro g en p e r o x id e. (. F ig u re 51) The o n ly d if f e r e n c e v;as th e u se o f p r e h e a te r. Due to th e slow d e c o m p o sitio n r a t e o f h y d ra z in e ( T a b le 4) w a te r was p re h e a te d p r i o r to e n t e r in g a u to c la v e to m inim ize te m p e ra tu re g r a d ie n t in s i d e th e a u to c la v e. S o lu tio n was p u rg ed w ith n itro g e n to p re v e n t th e d ec o m p o sitio n o f h y d ra z in e. E x p e rim e n ta l p ro c e d u re s a r e d e s c rib e d in s e c t io n Chem ical A naly sis For a n a ly s is o f h y d ra z in e C h em etrio s t e s t k i t, Model H-5 v/as u s e d. The t e s t k i t c o n ta in e d c o lo r com parators ( Ppm and t e s t am pules which c o n ta in e d p -d im e th y la m in o -b e n z a ld e h y d e to p roduce a y ello v ; c o lo r w ith hydrazine^*^^^ D is s o lv e d oxygen was a ls o a n a ly z e d alo n g w ith h y d ra z in e m easu rem en ts. C o lo rim e tric in d ig o -c a rm in e m ethod, d e s c r ib e d in s e c t io n 3.3.4, was u s e d f o r th e d e te r m in a tio n o f oxygen i n w a te r. H y d razin e does n o t i n t e r f e r e i n c o n c e n tra tio n s up to 1 ppm w ith th is method^

117 5.4 Results The t e s t m a tr ix f o r h y d ra z in e a d d i tio n s, a lo n g v â th some p e r t in e n t d a ta, i s shown i n T a b le 4. The c o r ro s io n p o t e n t i a l s o f P t, N i, Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800 v;ere m easu red i n h ig h te m p e ra tu re w a te r vo.th v a rio u s c o n c e n tr a tio n s o f h y d ra z in e. T here was l i t t l e d if f e re n c e i n h y d ra z in e c o n c e n tr a tio n betw een th e i n l e t and o u t l e t s tre a m s up to 200 C, Above t h i s te m p e ra tu re a s l i g h t d e c re a s e i n th e o u t l e t c o n c e n tr a tio n was n o tic e d. T here was no consum ption o f h y d ra z in e i n oxygen scav e n g in g s in c e th e fe e d w a te r was a lre a d y d e a e r a te d w ith n itr o g e n. The consu m ption o f h y d ra z in e above 200 C may be a s s o c ia te d w ith d ec o m p o sitio n r e a c tio n w hich form s ammonia and n itr o g e n. At h y d ra z in e c o n c e n tr a tio n s '^looo ppb o r above th e fe e d w a te r became s l i g h t l y a l k a l i n e. The o u t l e t stre a m i n m ost o th e r c a s e s?/as no more a l k a l i n e th a n th e i n l e t s tre a m, A t y p i c a l re s p o n s e o f th e c o r r o s io n p o te n t i a l w ith tim e a t 100 C i s shovm i n F ig u re 52. The i n i t i a l p o t e n t i a l dropped by s e v e r a l h u n d red m i l i v o l t s i n 5 to 10 h o u rs and became s te a d y i n ab o u t 15 h o u rs. T h is i n i t i a l drop i n p o t e n t i a l was a s s o c ia te d v/ith oxygen s c av en g in g in w ate r s in c e w a te r in th e a u to c la v e was s a tu r a te d w ith oxygen d u rin g s t a r t u p. The r e s u l t s a t d i f f e r e n t te m p e ra tu re s f o r th e in d i v id u a l m a te r i a ls a r e shown as a fu n c tio n o f h y d ra z in e c o n c e n tr a tio n i n F ig u re s 53 to 57, In c r e a s in g th e h y d ra z in e c o n c e n tr a tio n s from 20 ppb to 1,000 ppb s l i g h t l y lo w ered th e c o r r o s io n p o t e n t i a l s a f t e r w hich th e p o t e n t i a l s w ere r e l a t i v e l y u n a f f e c te d. In c re a s in g

118 th e te m p e ra tu re lo w ered th e p o t e n t i a l a t any h y d ra z in e c o n c e n tr a t io n s. A bout 1$0-200 mv change i n p o t e n t i a l was o b s e rv e d f o r te m p e ra tu re change from 100 C to 288 C. 99 ^ F ig u r e s 58 and 59 show th e e f f e c t o f a l lo y c o m p o sitio n s on th e c o r r o s io n p o t e n t i a l a t 200 C and 288 C a lo n g w ith e q u ilib r iu m p o t e n t i a l s f o r o x id a tio n r e a c t i o n o f h y d ra z in e, r e s p e c t i v e l y. S in c e w a te r v;as p u rg ed w ith n it r o g e n i n th e fe e d ta n k, p a r t i a l p r e s s u r e o f n itr o g e n was assum ed to be 1 a tm o s p h e ric p r e s s u r e. None o f th e m e ta ls fo llo w th e e q u ilib r iu m p o t e n t i a l s o f h y d ra z in e e l e c tr o d e. E x p e rim e n ta l v a lu e s a r e AOO-600 mv h ig h e r th a n e q u ilib r iu m p o t e n t i a l s. P la tin u m alw ays showed h ig h e s t p o t e n t i a l and th e lo w e s t p o t e n t i a l was f o r Type 504 s t a i n l e s s s t e e l. The p o t e n t i a l s o f o th e r m e ta ls w ere betv/een t h a t o f P t and Type 304 s t a i n l e s s s t e e l.

119 5.5 Discussion The d if f e r e n c e i n e q u ilib riu m p o t e n t i a l betw een o;^id a tio n and re d u c tio n r e a c tio n o f h y d ra z in e i s a b o u t V d ep endin g upon th e c o n c e n tr a tio n o f h y d ra z in e and ammonia and te m p e r a tu r e. E q u ilib riu m p o t e n t i a l o f r e d u c tio n r e a c tio n i s r a i s e d w ith in c r e a s in g...ra tio and d e c re a s e d i s th e o x id a tio n p o t e n t i a l w ith h y d ra z in e. None o f th e e x p e rim e n ta l v a lu e s f o llo w th e e q u ilib riu m p o t e n t i a l o f h y d ra z in e e le c tr o d e b u t l i e betw een e q u ilib riu m o x id a tio n and r e d u c tio n p o t e n t i a l s. T h is im p lie s t h a t th e p o t e n t i a l s d ev e lo p ed on th e m e ta ls fo llo v / m ixed p o t e n t i a l th e o r y. P o s s ib le an o d ic r e a c tio n s a r e o x id a tio n o f h y d ra z in e to n itr o g e n a n d /o r m e ta l o x id a tio n, w hereas.c a th o d ic r e a c t i o n s a re 1) re d u c tio n o f h y d ra z in e to ammonia 2) r e d u c tio n o f m e ta l o x id e and 3) r e d u c tio n o f w a t e r,, S in c e n o t much d if f e r e n c e i n c o n c e n tr a tio n o f h y d ra z in e b etw een i n l e t and e x i t s id e was o b s e rv e d, fo rm a tio n o f ammonia o r n itro g e n may n o t be s i g n i f i c a n t. A lloy dependence c o r r o s io n p o t e n t i a l a ls o i n d i c a t e t h a t m e ta l o x id a tio n a n d /o r o x id e r e d u c tio n may b e an im p o rta n t p a r t o f th e r e a c t i o n. The c o r r o s io n p o t e n t i a l s o f th e m e ta ls i n v;ater c o n ta in in g h y d ra z in e a re c lo s e to th e t h e o r e t i c a l h y drogen e l e c tr o d e p o t e n t i a l (s e e F ig u re 2 4 ). T h is im p lie s t h a t i n d e a e ra te d w a te r, r e d u c tio n o f w a te r may be a s i g n i f i c a n t c a th o d ic re a c tio n» The e f f e c t o f h y d ra z in e a d d i tio n on th e c o rro s io n p o t e n t i a l s o f v a rio u s m e ta ls i n o x y g e n a te d h ig h te m p e ra tu re v /a te r v;as s tu d ie d by Sykes,^^ ^ The r e s u l t s a t are shown in F igu re 47 fo r Type 304 s ta in le s s s te e l and F ig ure 48

120 101 : f o r In c o n e l 600. F or 10 ppm h y d ra z in e a d d itio n c o r r o s io n p o t e n t i a l s o f th e m e ta ls rem ain c o n s ta n t a t a l l c o n c e n tr a tio n s o f oxygen, w hereas 1 ppm h y d ra z in e shows in c r e a s in g tr e n d o f p o t e n t i a l a t oxygen c o n c e n tr a tio n s above ^1 ppm. S in ce h y d ra z in e r e a c t s vri.th oxygen i n th e w eig h t r a t i o o f 1 to 1, th e in c r e a s e i n p o t e n t i a l ab o v e^1 ppm o f oxygen i s due to th e in c o m p le te rem oval o f oxygen i n w a te r by h y d ra z in e. P o t e n t i a l s o f th e m e ta ls f o r 10 ppm h y d ra z in e and t h a t fo r 1 ppm v /ith oxygen c o n c e n tr a tio n s below ppm a r e c lo s e to th e v a lu e s i n d e a e ra te d v /a te r. T h is o b s e rv a tio n im p lie s t h a t h y d ra z in e a f f e c t s th e c o r r o s io n p o t e n t i a l m ainly by scavenging oxygen in h igh tem peratu re w ater. In d e a e ra te d h ig h te m p e ra tu re w a te r th e p o s s i b le r e a c tio n c o u p le s w ith h y d ra z in e a d d itio n, a r e m e ta l o x id a tio n and w a te r r e d u c tio n a n d /o r o x id a tio n and re d u c tio n o f h y d ra z in e. The l a t t e r r e a c tio n c o u p le s may be im p o rta n t a t te m p e ra tu re s above 2$0 C due to th e in c r e a s e in d e c o m p o sitio n r a t e o f h y d ra z in e a t th e s e te m p e ra tu re s.

121 TÎCST MATRIX FUR UYURAX1MF STUDY Temperature Dut 0^ In 0^ Out pu Out»2"4 C ppb ppb ppb ppb at 25 C at 25"C < 10 < < 10 < ,000 1, ,000 6,0 0 0 U loo 85 < < 10 < , ,000 < 10 < < 10 < loo 85 5 < , < ~ , <

122 '700 V loo^'c (aqh40h'(aq)^njg) - n = I a tm - ^ 4 H A j * 200 C -900dV- 250 C -I,0 0 0 'l,2 0 0 jr \0 ^ îpigure 9. p o te n tia l^! o

123 E X NHj (aq) + 2 OH (aq) -A/^ (aq) + 2 Hp Oft) + 2 s g z "5 600 I I Cone, of N2 H4 /(Gone, of NHj)^ ppm/(ppm)^ Figure 50. Equilibrium potentials of hydrazine reduction reaction

124 Figure.51. Experimental setup for hydrazine 1, D i s t i l l e d W ater '2. T r a n s f e r Pump 3. W ater P u r i f i c a t i o n S ystem, M illip o r e 4. C o n d u c tiv ity M eter 5. S torage Tank 6. D e a e ra tio n Tank 7. M ixing Tank 8. C hem ical M ete rin g Pump 9. C hem ical S to ra g e Tank 10. M ete rin g Pump 11. Fligh P re s su re Pump 12. P r e h e a te r 13. A utoclave 14. P r e s s u re Gauge.15. A fte r-c o o le r 16. Back P r e s s u r e R e g u la to r 17. D rain 105

125 9 V V I Figure 51. Experimental setup for hydrazine

126 1 c eu o CL c o tn O O O Wafer Qualify Temperafure '!00 C No H. Ouf ppb ppb \6 0 0 O2 Out ph In ph Out loppb < 5ppb Heating -200U _L Time, Hours F ig u re 52, C o rro s io n p o t e n t i a l s v e rs u s tim e a t 100 C

127 - T - T - r y Type Stainless Steel ^ o A ZSO'-C -^^_200 C ~~h-o 288 C _L ,000 10,000 Dissolved Hydrazine Concentration, ppb F ig u re 53. Cor3?osion p o t e n t i a l s o f Type 304 s t a i n l e s s s t e e l v e rs u s d is s o lv e d h y d ra z in e

128 Incone! > Ê o K A?po;c^ ^ c" K «250 C -800, 10 li_ 100, 1,0 0 0 Dissolved Hydrazine Concentration, ppb Figure 54. Corrosion potentials of Inconel 600 versus dissolved hydrazine 10,000

129 -200 In CO toy > E O ' C ~ 100 C J1 t_*250 C 288 C K-O A -800 ll ^ œ o 10,000 Dissolved Hydrazine Concentration, ppb Figure 55, Corrosion potentials of Incoloy 800 versus dissolved hydrazine o

130 -100 r N ickel \ - A u ^IOO C o.a 250 c O li_ ,000 Dissolved Hydrazine Concentration, ppb Figure 56. Corrosion potentials of nickel versus dissolved hydrazine 10,000

131 Platinum Or """~ C KO-*"*" C 250 C HO "A ^ , J _ i_l ,000 Dissolved Hydrazine Concentration,ppb Figure 57* Corrosion potentials of platinum versus dissolved hydrazine 1 0,0 0 0

132 X o -500 Temperature : C O... LEGEND P latinum Type Inconel Incoloy Nickel -600, ,000 Dissolved Hydrazine Concentration,ppb Figurj 58, Corrosion potentials versus dissolved hydrazine at 200 G

133 E Temperature : C LEGEND P latinum 0 Type Inconel Incoloy O Nickel o # 0 0-1,100-1,200 Dissolved Hydrazine Concentration, ppb Figure 59» Corrosion potentials versus dissolved hydrazine at 288^0

134 6. CORROSION POTENTIAL OF IRON-NICKEL-CHROMIUM ALLOYS IN WATER AT 2$0 C; THE EFFECT OF CHROMATE AND NITRATE 6,1 I n tr o d u c tio n C hrom âte an d n i t r a t e a r e w e ll knov/n o x id iz e r? W hile c h ro m â te i s e x te n s iv e ly u sed as a p a s s iv a t o r b ecau se o f i t s o x id iz in g c a p a c it y and f a s t r e d u c t io n r e a c t i o n, n i t r a t e was n o t r e g a rd e d a s a good p a s s iv a t o r due to i t s s lu g g is h r e a c t i o n ra te i"^ ^ ^ N i t r a t e an d ch ro m â te fre q u e n tly a f f e c t s t r e s s c o r r o s io n b e h a v io r o f m e ta ls m a in ly by p a s s iv a t io n phenom ena. N i t r a t e s a r e added i n b o i l e r w a te r to i n h i b i t s t r e s s c o r r o s io n c ra c k in g o f s te e l^ " ^ ^ \v h e re a s n i t r a t e s o lu ti o n s a r e Imovm to p ro d u ce s e v e re i n t e r g r a n u l a r s t r e s s c o r r o s io n c ra c k in g o f m ild s t e e l Chromâte i s a w id ely u s e d i n h i b i t o r f o r c o r r o s io n i n r e c i r c u l a t i n g c o o lin g w ater, such as engine co o lin g system s? A f te r th e u t i l i z a t i o n o f n u c le a r pow er p la n t a u s t e n i t i c s t a i n l e s s s t e e l s have e x h i b ite d s t r e s s c o r r o s io n c ra c k in g i n h ig h te m p e ra tu re w a te r i n th e p re s e n c e o f o x id iz in g species?chromium w hich d is s o lv e s from r e a c t o r m a te r i a ls can be o x id iz e d i n t o ch ro m âte by r a d i a t i o n e f f e c t and n i t r a t e can be c r e a te d from n it r o g e n c o n ta m in a tio n v ia r a d i a t i o n f lu x. T h is s tu d y i n v e s t i g a t e d th e e f f e c t o f sm all amount o f c h ro m âte and n i t r a t e p r e s e n t i n w a te r on th e c o r r o s io n p o t e n t i a l o f F e-n i-c r a l lo y s a t 250 C. The r e s u l t s w ith r e f r e s h e d a u to c la v e sy stem w ere com pared to t h a t v â th s t a t i c a u to c la v e, 115

135 Experimental R efreshed A utoclave System The e x p e rim e n ta l s e tu p f o r th e s tu d y w ith r e f r e s h e d a u to c la v e system i s shown i n F ig u re 3k* The w a te r was p u rg ed w ith n itr o g e n f o r d e a e r a tio n,? " d i a.x i" l o n g c y l i n d r i c a l specim ens w ere m ounted on T e flo n c o a te d s t a i n l e s s s t e e l h o ld e r (s e e F ig u re 7 ). M a te r ia ls f o r th e s tu d y w ere Type 30k s t a i n l e s s s t e e l, In c o n e l 600, n ic k e l and p la tin u m. 0,7 to 16 ppm n i t r a t e was added a s p o ta ss iu m n i t r a t e and 1,1 to 27 ppm c h ro m âte c o n c e n tr a tio n was ra n g e d p o ta ss iu m ch ro m ate. Sam ples w ere ta k e n from i n l e t and e x i t s id e f o r ch e m ical a n a ly s is and ph m e asu rem en ts. F or c o r r o s io n p o t e n t i a l m easurem ents o f th e m e ta ls c o n c e n tr a tio n s o f n i t r a t e and chrom ate w ere changed a f t e r s te a d y s t a t e p o t e n t i a l s w ere m a in ta in e d f o r 3 to 10 h o u rs. The d e t a il e d ex perim en tal pro ced ures were d escrib ed in s e c tio n k*3*'i* as S ta tic A utoclave System 4 l i t e r c a p a c ity o f In c o n e l 600 a u to c la v e v/as u sed f o r th e s tu d y. No l i n i n g v/as em ployed in s id e a u to c la v e, 0,7 to 23 ppm o f n i t r a t e a s sodium n i t r a t e and 0,6 to 24 ppm o f chrom ate a s p o ta ssiu m ch ro m ate v/ere added i n 2,7 l i t e r d e m in e ra liz e d d o u b le d i s t i l l e d v /a te r. D e a e ra tio n was p erfo rm e d by p u rg in g w ith a rg o n and th e oxygen l e v e l was found to be n e a r 20 ppb w ith in d ig o -c a rm in e m ethod ( s e c t io n 3, 3, 4)» Four h o u rs d e a e r a tio n was s u f f i c i e n t to low er th e oxygen le v e l. M a te ria ls used in th e experim ent

136 117 w ere P t, N i, Cr, F e, Type 30^ s t a i n l e s s s t e e l and In c o n e l 600, C o n fig u ra tio n o f w orking e le c tr o d e i s same as th a t f o r th e p o t e n t i a l m easurem ents i n r e f r e s h e d a u to c la v e s y ste m. I n i t i a l and f i n a l w a te r sam ples w ere c o l le c t e d f o r ch e m ica l a n a ly s is and ph m easu rem en ts. The p r e p a r a tio n o f Ag/AgCl r e f e r e n c e e le c tr o d e and p ro c e d u re s f o r specim en p r e p a r a tio n and p o t e n t i a l m easurem ents a re e x p la in e d in s e c t io n 3,3. 6,2,3 Chem ical A nalysis N i t r a t e c o n c e n tr a tio n s w ere a n a ly z e d w ith c o lo r im e tr ic m ethod, d e s c rib e d i n ASTM S ta n d a rd D e s ig n a tio n ; D C o lo r d e v e lo p in g a g e n t i s b ru c in e i n s tr o n g s u l f u r i c a c id s o l u t i o n. Ni.t r a t e io n r e a c t s w ith t h i s s o lu tio n to d evelop a y e llo w c o lo r. The a b s o rb an ce o f th e c o lo r was m easured w ith s p e c tro p h o to m e te r. F or m easurem ents o f chrom ate c o n c e n tr a tio n s ato m ic a b s o rp tio n s p e c tro p h o to m e te r was em ployed.

137 6.3 R esu lts T e st m a trix f o r chrom ate and n i t r a t e i n s t a t i c and r e f r e s h e d a u to c la v e sy stem s i s shown i n T a b le 3. W ith s t a t i c a u to c la v e sy stem consum ption o f ch ro m ate and n i t r a t e was o b s e rv e d to be p ro n o u n ced. Chrom ate c o n c e n tr a tio n s w ere n o t d e te c te d a f t e r th e t e s t f o r th e i n i t i a l c o n c e n tr a tio n s o f chrom ate up to 10 ppm. Only k ppm o f f i n a l c o n c e n tr a tio n o f chrom ate was d e te rm in e d f o r th e t e s t w ith 24 ppm o f chrom ate^ About one h a l f o f i n i t i s i l c o n c e n tr a tio n o f n i t r a t e was o b s e rv e d a f t e r each t e s t s. PH s w ere g e n e r a lly in c r e a s e d a f t e r th e t e s t w ith t h i s sy ste m. W hile s i g n i f i c a n t change i n w a te r c h e m is try was o b serv e d w ith s t a t i c a u to c la v e, r e s u l t s from r e f r e s h e d a u to c la v e system showed n o t much change i n c o n c e n tr a tio n o f chrom ate and n i t r a t e betw een i n l e t and o u t l e t s id e o f w a te r, a lth o u g h s m a ll consu m p tio n s o f th e s p e c ie s w ere n o tic e d. PH s o f i n l e t and o u t l e t w ere n e a r l y same w hich v/ere c lo s e to n e u t r a l a t room te m p e ra tu r e Chromate R efresh ed A utoclave System : The re s p o n s e o f c o r r o s io n p o t e n t i a l s o f Type 304 s t a i n l e s s s t e e l, In c o n e l 600, n ic k e l and p la tin u m w ith tim e i n w a te r c o n ta in in g 9.6 ppm o f chrom ate a t 230 C i s shown in F ig u re 60. S te a d y s t a t e c o r r o s io n p o t e n t i a l s w ere o b s e rv e d a f t e r ab o u t 10 h o u rs. A ll 4 m e ta ls e x h i b it e s s e n t i a l l y same p o t e n t i a l. F ig u re 6l shows th e e f f e c t

138 o f chrom ate a d d itio n on th e c o r r o s io n p o t e n t i a l o f th e m e ta ls a t 250 C a lo n g w ith th e therm odynam ic e q u ilib r iu m p o t e n t i a l s o f Cr0^""/Cr20^ r e a c tio n a t ph and 6.5 3, r e s p e c t i v e l y. As was o b s e rv e d i n F ig u re 60, fo u r m e ta ls a p p e a re d e s s e n t i a l l y same p o t e n t i a l s i n th e c o n c e n tr a tio n ra n g e s i n v e s t i g a t e d. I n c r e a s in g c o n c e n tr a tio n o f chrom ate 119 i n w ate r showed d e c re a s in g tr e n d o f p o t e n t i a l. About 80 mv d e c re a s e i n p o t e n t i a l was o b s e rv e d by changin g chrom ate c o n c e n tr a tio n s from ~1 ppm to ^^30 ppm. The r e a c tio n o f chrom ate to chrom ic o x id e i n aqueous s o lu tio n i s, + 10H + 6e (6-1 ) and th e e l e c tr o d e p o t e n t i a l C v o l t ) i s g iv e n by E j = E? H- lo g ph (6-2 ) a t 250 C 250" ^ ' lo g aq^ro^" 0.1?3pH (6-3 ) From e q u a tio n 6-3 j35 mv r i s e i n p o t e n t i a l p e r decade in c r e a s e i n c o n c e n tr a tio n o f ch ro m ate and 173 mv drop i n p o t e n t i a l w ith a u n i t in c r e a s e in ph a r e e x p e c te d a t 250 C. S in c e e q u ilib riu m p o t e n t i a l o f CrO^~/Cr^O^ r e a c t i o n i s d o m in an tly a f f e c te d by ph ch ange, th e d e c re a s in g tr e n d o f p o t e n t i a l s, i n F ig u re 6 l, w ith chrom ate a d d i tio n may be e x p la in e d by ph e f f e c t. The in c r e a s e in p o ta ssiu m chrom ate may s h i f t th e ph o f th e s o lu tio n s l i g h t l y to a l k a l i n e re g io n, s in c e p o ta ssiu m h y d ro x id e i s a s tr o n g b a s e w hereas chrom ic a c id i s knovm to be a weak a c id. M oreover, th e r e a c tio n o f chrom ate io n to form chrom ic o x id e consum es p ro to n by r e a c tio n 6-1, i t i s t h e r e f o r e

139 e x p e c te d t h a t consum ption o f chrom ate a ls o s h i f t th e ph o f s o l u t i o n to h ig h e r v a lu e. S ta tic A utoclave System : F ig u re 62 shows th e c o r r o s io n p o t e n t i a l re s p o n s e o f v a r io u s m e ta ls w ith tim e i n 10 ppm chrom ate s o lu tio n a t 2^0 C i n s t a t i c a u to c la v e. From T a b le 5 one can n o ti c e t h a t no chrom ate was d e te c te d a f t e r th e t e s t f o r th e c o n c e n tr a tio n o f ch ro m ate up to 10 ppm. S l i g h t l y in c r e a s e i n ph was a ls o o b s e rv e d, p o s s i b ly by r e a c t i o n 6-1. Sudden drop o f p o t e n t i a l was a p p e a re d a f t e r 30 to 40 h o u rs o f t e s t f o r a l l m e ta ls. A f te r th e drop o f p o t e n t i a l s o lu ti o n seem s to be v i r t u a l l y f r e e o f ch ro m a te. The tim e fo r th e sudden change i n p o t e n t i a l was found to be s h o r te n vri.th lo w e r c o n c e n tr a tio n o f ch ro m ate. The e f f e c t o f chrom ate c o n c e n tr a tio n on c o r r o s io n p o t e n t i a l o f th e m e ta ls i s shovm i n F ig u re 63. P o t e n t i a l s o f th e m e ta ls i n p u re w a te r a re shovm on th e l e f t hand s id e o f th e f ig u r e f o r th e p u rp o se o f c o m p ariso n. I n c r e a s in g i n i t i a l c o n c e n tr a tio n o f ch ro m ate e x h i b its d e c re a s in g tr e n d o f p o t e n t i a l f o r ch ro m ate c o n c e n tr a tio n up to 10 ppm. N o tic e t h a t no ch ro m ate was d e te c te d a f t e r th e t e s t s i n th e s e chrom ate c o n c e n tr a tio n ra n g e s. As m e n tio n e d e a r l i e r th e d e c re a s in g tr e n d o f p o t e n t i a l may be a s s o c ia te d w ith th e in c r e a s e i n ph by r e a c tio n 6-1. Sudden jump o f p o t e n t i a l from a b o u t mv to -100 mv was found f o r a l l m e ta ls a t 24 ppm ch ro m ate c o n c e n tr a tio n. I n t h i s p a r t i c u l a r c a se 4 PPm o f ch ro m ate was d e te rm ie d a f t e r th e t e s t. U n lik e th e p o t e n t i a l s fo r o th e r c o n c e n tr a tio n s o f chrom ate a l l m e ta ls

140 e x h i b it n e a r ly same p o t e n t i a l s. About 100 mv p o t e n t i a l d if f e r e n c e v/as o b se rv e d betw een s t a t i c and r e f r e s h e d a u to c la v e sy stem a t -^25 ppm chrom ate c o n c e n tr a tio n. A gain, t h i s d if f e r e n c e i n p o t e n t i a l may be r e s u l t e d from th e change in ph. 6.3,2 N i t r a t e R efreshed A utoclave System : The v a r i a t i o n o f c o rro s io n p o t e n t i a l s o f Type 304 s t a i n l e s s s t e e l, In c o n e l 600, n ic k e l and p la tin u m w ith tim e i s shown i n F ig u re 64. The tim e f o r re a c h in g s te a d y s t a t e c o r ro s io n p o t e n t i a l s o f th e m e ta ls a r e 15 to 20 h o u rs. F ig u re 65 shows th e e f f e c t o f n i t r a t e io n c o n c e n tr a ti o n on th e c o rro s io n p o t e n t i a l o f th e a l l o y sy stem s a t 250 C, From th e f ig u r e n o t much e f f e c t o f n i t r a t e a d d itio n was o b s e rv e d on th e c o r ro s io n p o t e n t i a l s o f th e m e ta ls. Only mv in c r e a s e i n p o t e n t i a l w ith c o n c e n tr a tio n change from 0,7 to 16 ppm was o b s e rv e d. C o rro s io n p o t e n t i a l s o f th e m e ta ls i n p u re w ate r w ith 10 to 20 ppb d is s o lv e d oxygen c o n c e n tr a tio n were shown on th e l e f t hand s id e o f th e f ig u r e. I t a p p e a re d t h a t a d d i tio n o f 1 to 16 ppm n i t r a t e io n to h ig h te m p e ra tu re w a te r d id n o t a f f e c t c o rro s io n p o t e n t i a l o f th e a l lo y s, a lth o u g h i t i s known to be an o x id i z e r. T h is phenomenon i s p o s s ib ly due to e i t h e r th e s lu g g is h n e s s o f th e r e d u c tio n r e a c tio n ( s te e p e r T a f e l s lo p e ) o r d if f u s io n c o n t r o lle d c a th o d ic p ro c e s s o f n i t r i e r e d u c tio n r e a c t i o n. The r e a c tio n betv/een n i t r a t e and n i t r i t e i s, 2H'^ + 2e (6-4 )

141 122 and by N e rn s t e q u a tio n, ^ ^ go _ 2 ^, 2 ^ 2 5. at 250 C ^N o; E^^q= O.IOifpH lo g (6-6 ) % o - As n i t a t e to n i t r i t e r e a c tio n p ro c e e d s, ph in c r e a s e s and th e NO^/NOg r a t i o d ro p s down. B oth o f th e s e two e f f e c t s lo v /er th e e q u ilib riu m p o t e n t i a l o f th e r e a c tio n by e q u a tio n 6-6. The e q u ilib r iu m p o t e n t i a l s o f NO^/NO^ r e a c tio n w ith two d i f f e r e n t c o n c e n tr a tio n r a t i o s o f th e s e io n s a t n e u t r a l ph w ere shown on th e r i g h t hand s id e o f th e f ig u r e. E x p e rim e n ta l v a lu e s o f p o t e n t i a l showed ab o u t 400 to 700 mv lo w er v a lu e s.-than therm o dynamic e q u ilib riu m p o t e n t i a l o f th e r e a c t i o n. P la tin u m e x h ib ite d a b o u t 200 mv h ig h e r v a lu e th a n F e-h i-c r a l l o y s. A llo y s o th e r th a n p la tin u m showed n e a r ly same c o r r o s io n p o t e n t i a l. S ta tic A utoclave System : The change i n c o r r o s io n p o t e n t i a l o f th e a l lo y s w ith tim e i n s t a t i c a u to c la v e i s shown i n F ig u re 67. U n lik e F ig u re 64 c o n tin u o u s d e c re a s e i n p o t e n t i a l o f th e m e ta ls was o b s e rv e d. T h is may be r e s u l t e d from e i t h e r th e consum ption o f oxygen i n th e w a te r o r d e c re a s e in c o n c e n tr a tio n o f n i t r a t e a s r e d u c tio n r e a c tio n p ro c e e d s, o r b o th. F ig u re 67 shows th e e f f e c t o f n i t r a t e io n c o n c e n tr a tio n on th e c o r r o s io n p o t e n t i a l s o f th e a l l o y s.

142 123 For com parison c o r r o s io n p o t e n t i a l s o f th e a l lo y s i n p u re w a te r w ith same oxygen c o n c e n tr a tio n være i n d i c a t e d on th e l e f t hand s id e o f th e f ig u r e. S im ila r to th e d a ta T /ith r e f r e s h e d a u to c la v e system n i t r a t e io n d id n o t a f f e c t th e c o r r o s io n p o t e n t i a l s o f F e-n i-c r a l l o y s. B ut s l i g h t in c r e a s e i n p o t e n t i a l vo.th p la tin u m was o b s e rv e d a t n i t r a t e c o n c e n tr a tio n s ab o u t 5 ppm to a p p ro ac h th e p o t e n t i a l t h a t in d i c a t e d in F ig u re 65* P la tin u m alw ays showed h ig h e s t v a lu e o f th e p o t e n t i a l and lo w e s t was g e n e r a lly ir o n. S in c e th e p o t e n t i a l d e v e lo p ed in v ;a ter c o n ta in in g n i t r a t e io n does n o t fo llo w e q u ilib riu m p o t e n t i a l o f NO^/NO^ r e a c tio n and a l lo y dependence c o r r o s io n p o t e n t i a l was o b s e rv e d, m ixed p o t e n t i a l co n c e p t i s th e.r e a s o n a b le i n t e r p r e t a t i o n f o r th e o b s e rv e d phenom ena. P o s s ib le a n o d ic r e a c t i o n i s m e ta l o x id a tio n and c a th o d ic r e a c tio n s a re r e d u c tio n o f n i t r a t e, r e d u c tio n o f r e s i d u a l oxygen p r e s e n t i n th e s o lu tio n and r e d u c tio n o f w a te r. In F ig u re 65 and 67 v i r t u a l l y no e f f e c t o f n i t r a t e io n c o n c e n tr a tio n was o b s e rv e d on th e c o r r o s io n p o t e n t i a l o f th e a l l o y s. H ence, th e p la u s i b le r e a c tio n co u p le may be m e ta l o x id a tio n and oxygen r e d u c tio n a n d /o r w a te r re d u c tio n depending upon th e oxygen c o n c e n tr a tio n. F or th e c o n c e n tr a tio n o f n i t r a t e i n v e s t ig a t e d r e a c tio n o f n i t r a t e may be d if f u s io n c o n t r o lle d o r due to th e s lu g g is h n e s s o f th e r e a c tio n r a t e. N itr a te may n o t e x te n s iv e ly ta k e p a r t in th e d e v e lo p ment o f c o rro s io n p o t e n t i a l o f th e a l l o y s.

143 C onclusions E f f e c t o f chrom ate and n i t r a t e p r e s e n t i n w a te r on th e c o r r o s io n p o t e n t i a l o f s e v e r a l F e-n i-c r a l lo y s and p la tin u m was s tu d ie d a t 250 C. The r e s u l t s v /ith s t a t i c a u to c la v e and r e f r e s h e d a u to c la v e sy stem w ere com pared. B ased on th e e x p e rim e n ta l o b s e r v a tio n s follovrf.ng c o n c lu s io n s can be dr aim. 1) Chrom ate in c r e a s e d th e p o t e n t i a l o f th e a l lo y s as much a s 600 mv. 2) A ll m e ta ls showed e s s e n t i a l l y same c o r r o s io n p o t e n t i a l w hich was c lo s e to th e therm odynam ic e q u ilib r iu m p o t e n t i a l o f CrO^~ /C r^o ^ r e a c t i o n. T h is i n d i c a t e d th a t th e p o t e n t i a l s d ev e lo p ed on th e a l lo y s i n h ig h te m p e ra tu re w a te r c o n ta in in g s m a ll am ount o f chrom ate m ight fo llo w th e e q u ilib r iu m p o t e n t i a l o f CrO^"/Cr^O^ r e a c t i o n. 3 ) I n c r e a s in g chrom ate c o n c e n tr a tio n s l i g h t l y d e c re a s e th e p o t e n t i a l o f th e a l l o y s, p o s s i b ly due to th e change in ph. 4) 1 to 23 ppm o f n i t r a t e a d d i tio n s d id n o t a f f e c t th e c o r r o s io n p o t e n t i a l s o f th e a l l o y s, 5) D e v ia tio n o f o b s e rv e d p o t e n t i a l s o f th e m e ta ls from e q u ilib r iu m p o t e n t i a l o f NOl/NO^ r e a c t i o n and a l lo y dependence c o r r o s io n p o t e n t i a l in d i c a t e d t h a t th e p o t e n t i a l s o f m e ta ls d ev e lo p ed i n th e s o lu ti o n fo llo iv ed m ixed p o t e n t i a l th e o r y. 6) S t a t i c a u to c la v e was found to be in a d e q u a te system f o r th e p r e s e n t s tu d y due to th e change i n v /a ter c h e m is try i n s id e a u to c la v e. T h is change i n w a te r c h e m is try was p a r t i c u l a r l y pro n o u n ced w ith ch ro m ate s o l u t i o n.

144 Table 5. test MATRIX FOR CHROMATE AllD NITRATE STUDY S o lu tio n I n i t i a l Cone. ppm S ta tic A utoclave R efreshed A utoclave F in a l I n i t i a l F in a l I n l e t O u tle t I n le t. O u tle t Cone. ppm ph Cone, Cone, ph ppm ppm ph ph 0.6 ~ ,0 8,1 1 ^ ,0 Chrom ate ^ < N i t r a t e ,

145 Tem perature: 250 C System : R efresh in g A utoclave H H e a tin g Legend GrO^ In : 9.6 ppm CrO^ Out: 9.5 PPm 0 2 ln : ppb 6db H i P t 0 $ Time, h o u rs Figure 60, Corrosion potentials versus time in chromate solution

146 4 0 0 C r O j/c r g O g at ph = ? C r O ^ /C r g O s at ph = Ô -100 LEGEND o Pt O 600 T e m p e r a t u e 2 $ 0 C C one, of Og : ppb S y s te m : R efrestim g A u to cla v e I 5 10 C oncentra tio n of Chromate Ion, ppm Figure 61, Corrosion potentials versus dissolved chromate at 250 C 3 0

147 \ H e a tin g S -300 c -400 T em p e ra tu r e C S y s te m : S t a t ic A u to c la v e CrO% In itia l ; 10 ppm CrO ^ F in a l: Not D e te c te d Og In itia l: ~ 2 0 p p b ph Final LEGEND P t F ig u re Time, Hours C o rro s io n p o t e n t i a l s v e rs u s tim e i n chrom ate s o lu tio n 5 0

148 -100 > -300 Temperature ' C System : Static Autoclave LEGEND «o ^ -500 Pt. ^ -700 o I Initial Contcentration of Chromate Ion, ppm Figure 63. Corrosion potentials versus dissolved chromate at 230 C 30

149 Legend Ni P t T e m p e ra tu re : 250 c System : R efresh in g A utoclave NO^ In : 0,7 3 ppm NO^ O ut: 0,6 3 ppm O2 In : ppb ph O ut: 7,2 4 H e a tin g -600 I 3 10 Tim e, h o u rs Figure 64. Corrosion potentials versus time in nitrate solution 23

150 LEGEND P t A Ni O T e m p e r a tu r e C C one, of Og : p p b S y s t e m : R e fr e stiin g A u to c la v e CNOj/Cfjog^iO p p m /p p m p p m /p p m I Conentration of N itra te Io n, ppm J _ Figure 65. Corrosion potentials versus dissolved nitrate at 250 C

151 k H e a tin g -200 T e m p e ra tu r e : C S y s te m : S t a t ic A u t o c la v e N O % ln itial: 2 5 p p m N O 3 F inal : 15 ppm O2 I n it i a l ~ 2 0 pp b ph In itia l ; 7.3 ph F in a l: o g LEGEND Pf Time, Hours F ig u re 66, C o rro s io n p o t e n t i a l s v e rs u s tim e i n n i t r a t e s o lu ti o n

152 Oh ri LEGEND Ni Or Fe. Pt. T e m p eratu re: 250 C System : S ta tic A utoclave * _i L _L _L Initial Concentration of Nitrate Ion, ppm Figure 67» Corrosion potentials versus dissolved nitrate at 2$0 C 30

153 7.. ELECTR0CHEI4ICAL KINETICS OF TYPE 304 STAINLESS STEEL IN HIGH TEMPERATURE OXYGENATED WATER 7.1 I n tr o d u c tio n F o r l a s t 13 y e a rs many a tte m p ts have been made to s tu d y th e e le c tr o c h e m ic a l k i n e t i c s o f Type 304 s t a i n l e s s s t e e l a t te m p e ra tu re s above b o i l i n g p o in t i n aqueous s o lu ti o n s. The m ain p u rp o se o f th e s e s tu d ie s was to i n v e s t i g a t e th e c o r r o s io n problem in n u c le a r pov/er p l a n t. The m ajo r c o rro s io n p roblem s i n BWR i s th e s t r e s s c o r r o s io n c ra c k in g o f s e n s i t i z e d Type 304 s t a i n l e s s s t e e k w hich i s l a r g e l y dependent upon th e c o n c e n tr a tio n o f d is s o lv e d oxygen i n - c o o l a n t, w a t e r, ' C o n seq u e n tly, la r g e e f f o r t s have been c o n c e n tr a te d to th e s tu d y o f e le c tro c h e m ic a l b e h a v io r o f Type 304 s t a i n l e s s s t e e l i n h ig h te m p e ra tu re d e a e ra te d o r, i n some c a s e s, a e r a te d w a te r i n c o n ju n c tio n vn.th th e s t r e s s c o r r o s io n t e s t, J o n e s^ ^ ^ ^ u sed p la tin u m w ire as a r e f e r e n c e e le c tr o d e f o r s tu d y in g th e e le c tr o c h e m ic a l b e h a v io r o f Type 304 s t a i n l e s s s t e e l i n h ig h te m p e ra tu re w a te r c o n ta in in g v a r io u s c o n c e n tr a tio n s o f c h lo r id e (0-5 N ), H uebner e t, a l, (47) s tu d ie d th e p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800 i n w a te r c o n ta in in g 20 ppm s u l f a t e a t 300 C. They em ployed e x t e r n a l r e f e r e n c e e l e c tr o d e f o r th e i n v e s t i g a t i o n, F u g ii a ls o u se d e x t e r n a l r e f e r e n c e e l e c tr o d e f o r p o l a r i z a t i o n s tu d ie s o f a number o f m e ta ls, in c lu d in g Type 304 s t a i n l e s s s t e e l, i n 0.1 N sodium s u l f a t e a t te m p e r a tu r e s up to 290 C, He a ls o s tu d ie d th e e f f e c t o f oxygen c o n c e n tra tio n s -' on th e p o l a r i z a t i o n b e h a v io r o f m e ta ls i n h ig h te m p e ra tu re h ig h p r e s s u r e w a te r. He u s e d 1 l i t e r c a p a c ity o f s t a t i c a u to c la v e 134

154 135 and d is s o lv e d oxygen c o n c e n tr a tio n s v;ere n o t p r e c i s e ly m easu red. For t h i s re a s o n h is s tu d y was a q u a n t i t a t i v e i n v e s t i g a t i o n r a t h e r th a n a q u a n t i t a t i v e one. In d ig and M c llre e ^ ^ '^ ^ ^ ^ ^ ^ s tu d ie d th e p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l in d e a e ra te d 0.01 ÏÏ sodium s u l f a t e a t 274^0, A Ag/AgCl e l e c tr o d e w ith 0,01 N KCl was th e ' ' i n t e r n a l r e f e r e n c e e le c tr o d e f o r t h i s i n v e s t i g a t i o n. From th e s e in v e s t i g a t i o n s one can r e a l i z e t h a t a number o f d i f f e r e n t ty p e s o f r e f e r e n c e e le c tr o d e ; v;ere u sed f o r th e e x p e rim e n ts. A lso, v a rio u s c o n c e n tr a tio n s o f sodium s u l f a t e w ere ra n g e d f o r th e s tu d y. In s p i t e o f th e above m e n tio n e d a tte m p ts a more s y s te m a tic s tu d y i s n e c e s s a ry to i n v e s t i g a t e th e e f f e c t o f d is s o lv e d oxygen c o n c e n tr a tio n s on th e c o r r o s io n k i n e t i c s o f Type 304 s t a i n l e s s s t e e l in h ig h te m p e ra tu re h ig h p r e s s u r e w a te r. T h is s tu d y, th e r e f o r e, i n v e s t i g a t e d th e e le c tr o c h e m ic a l k i n e t i c s o f Type 304 s t a i n l e s s 's t e e l i n w a te r a t te m p e ra tu re s 100 to 250 C, Sodium s u l f a t e v;as added to in c r e a s e th e c o n d u c tiv ity o f e l e c t r o l y t e. To s tu d y th e lo n g te rm b e h a v io r o f anodic k i n e t i c s c u r r e n t decay e x p e rim e n ts w ere p erfo rm ed a t c o n t r o lle d p o t e n t i a l s. The e f f e c t o f d is s o lv e d oxygen c o n c e n tr a tio n on th e c a th o d ic k i n e t i c s o f Type 304 s t a i n l e s s s t e e l was s tu d ie d a t te m p e ra tu re s 100 to 230 C i n w a te r c o n ta in in g v a rio u s c o n c e n tr a tio n s o f d is s o lv e d oxygen.

155 E x p e rim e n ta l 7.2,1 A nodic K in e tic s A 4 l i t e r c a p a c ity o f In c o n e l 600 a u to c la v e was th e e le c tr o c h e m ic a l c e l l f o r th e i n v e s t i g a t i o n. The s tu d y f o r a n o d ic k i n e t i c s o f Type 304 s t a i n l e s s s t e e l was made in a s t a t i c a u to c la v e. No l i n i n g was em ployed in s id e th e a u to c la v e. D ouble d i s t i l l e d w a te r ( 0.5 Nohm/cm s p e c i f ic r e s i s t i v i t y ) was u s e d f o r p re p a r in g v a r io u s c o n c e n tr a tio n s o f sodium s u l f a t e s o lu ti o n. 2.7 l i t e r t e s t s o lu tio n was p u rg e d w ith arg o n f o r a t l e a s t 6 h o u rs, ^ " d i a.x i" l o n g c y l i n d r i c a l ty p e o f quench a n n e a le d Type 304 s t a i n l e s s s t e e l m ounted on T e flo n c o a te d s t a i n l e s s s t e e l h o ld e r was th e w orking e le c tr o d e (F ig u re 7 ). C om p o sitio n, th e rm a l h i s t o r y and m ic r o s tr u c tu re o f th e t e s t e l e c tr o d e a r e desc r ib e d i n A ppendix 2. Two p ie c e s o f p la tin u m s h e e t w ere u s e d a s c o u n te r e l e c tr o d e s. I n t e r n a l r e f e r e n c e e l e c tr o d e was th e Ag/AgCl e l e c tr o d e w ith 0.01 N K C l(f ig u re 3 0 ), L uggin c a p i l l a r y t i p ( f in e z i r c o n ia tu b in g ) was p la c e d betw een worlcing e le c tr o d e and p la tin u m c o u n te r e l e c tr o d e. D is ta n c e o f L uggin c a p i l l a r y t i p from th e w orking e le c tr o d e s u r f a c e was a b o u t 2 mm. E le c tro d e arra n g e m e n t in s i d e th e a u to c la v e i s shovra i n F ig u re 68. P la tin u m c o u n te r e le c tr o d e s w ere im m ersed i n aqua r e g i a f o r 10 to 20 m in u te s, th e n r i n s e d th o ro u g h ly v/ith d o u b le d i s t i l l e d v /a ter p r i o r to p la c in g them in th e a u to c la v e f o r th e f i r s t p o l a r i z a t i o n e x p e rim e n t. No f u r t h e r c le a n in g was made vn.th th e ' e l e c tr o d e s f o r l a t e r e x p e rim e n ts, u n le s s th e s u r f a c e o f th e e le c tr o d e was co n sid e red to be contam inated. Working e le c tro d e v/as

156 137! p o lis h e d ivith 600 g r id s i l i c o n c a rb id e p a p e r and d e g re a se d w ith aceton^ th e n r in s e d th o ro u g h ly v ;ith d o u b le d i s t i l l e d w ate r b e fo re p la c in g i t in th e a u to c la v e. The d e t a il e d m ethod fo r th e p r e p a r a tio n o f Ag/AgCl r e f e r e n c e e l e c tr o d e i s describ ed in se c tio n A ardvark p o t e n t i o s t a t, Model No.V was u s e d f o r b o th p o l a r i z a t i o n s tu d y and c u r r e n t decay e x p e rim e n ts. P o t e n t i a l was changed m a n u ally. Scan d ir e c ti o n was c a th o d ic to an o d ic u n le s s th e d ir e c ti o n i s in d i c a t e d v /ith arro w s i n th e f ig u r e s, C ath o d ic K in e tic s Owing to th e consum ption o f oxygen in th e system ( s e c t io n ), r e f r e s h e d a u to c la v e system was em ployed fo r t h i s i n v e s t i g a t i o n. The r e f r e s h e d a u to c la v e system i s d e s c rib e d i n s e c t io n S u lf a t e c o n c e n tr a tio n v;as a d ju s te d i n th e ta n k s. p r i o r to ' s t a r t i n g th e e x p e rim e n t. S in ce c a p a c it ie s o f ta n k no, 6 and n o, 7 w ere80 and 120 k i l o l i t e r, r e s p e c t i v e l y, volum e o f th e s o lu tio n was s u f f i c i e n t f o r each e x p e rim e n t, C h em etrics d is s o lv e d oxygen t e s t k i t was u se d f o r th e c h e m ical a n a ly s is ( s e c t io n ), E x p e rim e n ta l r e s u l t s w ere b a s e d on o u t l e t c o n c e n tra tio n o f d is s o lv e d oxygen. I n l e t concent r a t i o n s o f oxygen w ere a ls o m easured o c c a s io n a lly f o r com paring w ith o u t l e t v a lu e s. P r e p a r a tio n o f e le c tr o d e s and t h e i r arrangem ent in s id e th e a u to c la v e w ere same a s th a t f o r th e s tu d y o f an o d ic k i n e t i c s o f Type 304 s t a i n l e s s s t e e l,. F or room te m p e ra tu re p o l a r i z a t i o n

157 138 s tu d y 600 ml g la s s b e a k e r w hich c o n ta in e d 400 ml t e s t s o lu ti o n was th e e le c tr o c h e m ic a l c e l l. S a tu r a te d ca lo m el e le c tr o d e was u se d f o r th e r e f e r e n c e e le c tr o d e. Same p o t e n t i o s t a t, A ardvark Model No, V, a s was u s e d f o r th e s tu d y o f an o d ic k i n e t i c s was u t i l i z e d f o r th e i n v e s t i g a t i o n. U n lik e th e an o d ic p o l a r i z a t i o n s tu d y, p o t e n t i a l s c a n n e r, B rinkm an SMP 69? was u sed f o r sw eeping th e p o t e n t i a l.

158 U Results E f f e c t o f Scan R ate The e f f e c t o f sc a n r a t e on th e p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l was i n v e s t i g a t e d a t room te m p e ra tu re and 230 C, r e s p e c t i v e l y. F ig u re 69 shows th e e f f e c t o f s c a n r a t e on p o l a r i z a t i o n cu rv e o f Type 304 s t a i n l e s s s t e e l a t room te m p e r a tu r e. S o lu tio n was a i r s a t u r a t e d 0,1 N sodium s u l f a t e. T h ree d i f f e r e n t s can r a t e s.were chosen f o r th e s tu d y. S in c e th e p o t e n t i a l s c a n n e r in c r e a s e d p o t e n t i a l s te p v /is e, tim e was programmed., f o r ev e ry 10 mv change o f p o t e n t i a l. A nodic p a r t o f th e p o l a r i z a t i o n cu rv e was a f f e c t e d s i g n i f i c a n t l y by th e s c a n r a t e, w hereas c a th o d ic cu rv e was found to be r e l a t i v e l y u n a f f e c te d. I t i s a w e ll known f a c t t h a t p a s s iv e c u r r e n t d e n s ity i n a n o d ic p o l a r i z a t i o n c u rv e i s a s tr o n g fu n c tio n o f sc a n r a t e and v/as o b s e rv e d i n t h i s s tu d y. H ig h er v a lu e o f l i m i t i n g c u r r e n t d e n s ity a p p e a re d w ith 10 mv/2 se c o n d s s can r a t e, b u t w ith th e s c a n r a t e s o f 10 mv/200 s e c, and 10 mv/20 s e c, a lm o s t same v a lu e o f c u r r e n t d e n s ity was n o tic e d. T a f e l s lo p e o f c a th o d ic p o l a r i z a t i o n c u rv e rem a in e d u n a f f e c te d by th e change i n sc a n r a t e. F ig u re 70 and 71 show th e e f f e c t o f s can r a t e on th e p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l in d e a e ra te d O d W and 0,01 H sodium s u l f a t e a t 250 C, r e s p e c t i v e l y, 30 mv p o t e n t i a l was in c r e a s e d e v e ry 2 m in u te s f o r one t e s t and th e o th e r t e s t was q u a s i s te a d y s t a t e ty p e o f e x p e rim e n t. C u rre n t v;as m easured a f t e r 20

159 140 ; m in u tes a t each p o t e n t i a l u n le s s s te a d y s t a t e v a lu e was m a in ta in e d w ith in t h i s tim e. When no a p p r e c ia b le d r i f t i n c u r r e n t was o b s e rv e d f o r 3 m in u te s, th e v a lu e o f c u r r e n t was re g a rd e d a s a s te a d y s t a t e v a lu e. As e x p e c te d, th e p o l a r i z a t i o n c u rv e was s h i f t e d to th e r i g h t hand s id e w ith f a s t e r s c a n. W hile g e n e ra l shape o f p o la r iz a t io n cu rv e betw een th e s e two sc a n r a t e was v /e ll c o r r e l a te d i n 0.1 N sodium s u l f a t e, th e r e s u l t i n R sodium s u l f a t e w ith f a s t e r scan d id n o t r e v e a l im p o rta n t t r a n s i t i o n o f p o l a r i z a t i o n shape w hich was c l e a r l y o b se rv e d w ith slo w e r sc a n r a t e. The same phenomenon was o b se rv e d by H uebner e t. a l^ ^ ^ ^ F ig u re 72 i s th e r e p r o d u c tio n o f t h e i r r e s u l t s. S a tu r a te d c a lo m el e l e c tr o d e was th e e x te r n a l r e f e r e n c e e l e c tr o d e f o r t h e i r stu d y and t e s t e l e c tr o d e was s e n s i t i z e d Type 304 s t a i n l e s s s t e e l. S in ce v a lu e s o f th e p o t e n t i a l v â th e x t e r n a l r e f e r e n c e e l e c tr o d e can n o t be e a s i l y c o n v e rte d to th e s ta n d a r d hydrogen s c a le a t h ig h te m p e ra tu re, th e y p l o t t e d th e p o t e n t i a l w ith t r u e p o l a r i z a t i o n s c a l e. D is tin c t t r a n s i t i o n o f p o l a r i z a ti o n shape was o b s e rv e d w ith s lo w e r scan r a t e, w hereas f a s t e r sc a n r a t e d id n o t show t h i s t r a n s i t i o n. B ased on th e s e e x p e rim e n ta l o b s e r v a tio n s s lo w e r scan r a t e was ch o sen f o r th e an o d ic p o l a r i z a t i o n s tu d y o f Type 304 s t a i n l e s s s t e e l. For c a th o d ic p o l a r i z a t i o n stu d y 10 mv/20 seconds scan r a te was u sed.

160 Effect of Sulfate Concentration E f f e c t o f s u l f a t e io n c o n c e n tr a tio n on th e an o d ic p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l a t 230 C i s shovm in F ig u re 73. The IE -d ro p betw een w orking e le c tr o d e and r e f e r e n c e e l e c tr o d e i n N sodium s u l f a t e was c a lc u la te d and found to be o f th e o rd e r o f some te n s o f mv. No IE c o r r e c tio n, t h e r e f o r e, was a p p lie d. C o rro sio n p o t e n t i a l shows d e c re a s in g tr e n d w ith in c r e a s in g s u l f a t e c o n c e n tr a tio n s. P a s s iv e c u r r e n t d e n s i t i e s a p p e a re d n e a rly same i n th e ra n g e o f s u l f a t e c o n c e n tr a tio n i n v e s t i g a t e d, v/hereas th e p o t e n t i a l o f s h a rp tr a n s p a s s iv e peak was d e c re a s e d vd.th in c r e a s in g s u l f a t e c o n c e n tr a tio n. S m all p ealis o f c u r r e n t ap p e arin g a t p o t e n t i a l s -600 to -300 mv may be a s s o c ia te d w ith Fe^O ^/Fe-O ^, NiO /N i a n d /o r N i^^/n i t r a n s i t i o n s (F ig u re 4)» A f te r th e s h a rp tr a n s p a s s iv e peak s e c o n d a ry p a s s iv a t io n was o b s e rv e d. The p a s s iv e c u r r e n t d e n s i t i e s were n e a r l y same as t h a t f o r p rim a ry p a s s iv a t io n. The r a p i d in c r e a s e i n c u r r e n t a t th e p o t e n t i a l s above 400 mvjj i s a s s o c ia te d w ith th e oxygen e v o lu tio n r e a c t i o n. E f f e c t o f s u l f a t e c o n c e n tr a tio n on th e c a th o d ic p o l a r i z a t i o n o f Type 304 s t a i n l e s s s t e e l i n o x y g en a ted w a te r a t room te m p e ra tu re and 230 C i s shown i n F ig u re 74 and 75, r e s p e c t iv e l y. F or t h i s p a r t i c u l a r s tu d y o f oxygen r e d u c tio n k i n e t i c s a t 250 C 4 l i t e r c a p a c ity o f s t a t i c au to clav e which was made o f In co n el 600 was em ployed. At room te m p e ra tu re s u l f a t e c o n c e n tr a tio n d id n o t a f f e c t th e re d u c tio n k i n e t i c s o f oxygen, w hereas d e c re a s in g tr e n d o f p o t e n t i a l f o r th e c a th o d ic r e a c tio n o f oxygen v /ith s u l f a t e c o n c e n tr a tio n was o b s e rv e d a t C.

161 142; T a f e l s lo p e s w ere n o t a f f e c te d by s u l f a t e c o n c e n tr a tio n s. D is tin c t l i m i t i n g c u r r e n t d e n s i t i e s w ere n o t o b serv ed a t 250 C due to th e o v e rla p p in g o f h ydrogen e v o lu tio n r e a c t i o n R everse Scan F ig u re 76 shows th e e f f e c t o f r e v e r s e s c a n on th e an o d ic k i n e t i c s o f Type 304 s t a i n l e s s s t e e l i n 0,01 N sodium s u l f a t e s o lu ti o n a t 250'^C, P o t e n t i a l sw ept from c a th o d ic to a n o d ic, th e n th e s tu d y w ith r e v e r s e scan was i n v e s t i g a t e d. No sh a rp tr a n s p a s s iv e peak a p p e a re d upon re v e r s e s can and c u r r e n t d e n s ity shov/ed lo w e r v a lu e on r e v e r s e scan th a n th a t on fo rw a rd. E f f e c t o f scan d ir e c t i o n was a ls o s tu d ie d fo r c a th o d ic p o l a r i z a t i o n b e h a v io rs o f oxygen r e d u c tio n r e a c tio n i n 0,1 N sodium s u l f a t e a t 250 C w ith r e f r e s h e d a u to c la v e sy ste m. F i r s t scan was from o n odic to c a th o d ic, th e n r e v e r s e th e s c a n d ir e c ti o n. Hydrogen p e ro x id e c o n c e n tr a tio n was d e te rm in e d alo n g w ith oxygen c o n c e n tr a tio n m easurem ent a t open c i r c u i t and a f t e r th e f i r s t sc a n o f p o l a r i z a t i o n s tu d y, C h em etrics t e s t k i t was u se d f o r b o th m e asu rem en ts. As was o b se rv e d i n p u re w a te r a b o u t 50 ppb o f hydro g en p e ro x id e was d e te rm in e d a t open c i r c u i t and in c r e a s e d c o n c e n tr a tio n o f p e ro x id e (<- ^100 ppb) was d e te c te d a f t e r th e p o l a r i z a t i o n. D is tin c t T a f e l s lo p e a p p e a re d v /ith back s c a n. E a rly w o rk ers o b se rv e d t h i s phenomenon upon s tu d y in g th e r e d u c tio n k i n e t i c s o f oxygen a t room te m p e ra tu re w ith n o b le m e ta ls, su ch as p la tin u m and gold^"^^^ They found t h a t re p ro d u c ib le T a fe l s lo p e was o b ta in e d a f t e r th e b u ild up o f s te a d y s t a t e c o n c e n tr a tio n o f h y drogen p e r o x id e. B ased on t h e i r

162 : o b s e r v a tio n and p r e s e n t r e s u l t th e n o n li n e a r i ty o f T a.fel s lo p e n e a r open c i r c u i t p o t e n t i a l can be r e l a t e d to th e b u il d up o f h y drogen p e ro x id e c o n c e n tr a tio n, E f f e c t o f T em p eratu re E f f e c t o f te m p e ra tu re on th e an o d ic and c a th o d ic p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l i n o x y g e n a te d h ig h te m p e ra tu re w ate r w ith 0,1 N sodium s u l f a t e i s shov/n in F ig u re 78 and 79, r e s p e c t iv e l y. C o rro s io n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l d e c re a s e d w ith in c r e a s in g te m p e ra tu r e. About one decade in c r e a s e in p a s s iv e c u r r e n t d e n s ity was o b serv e d w ith th e te m p e ra tu re change from 100 to 230 C. S harp tr a n s p a s s iv e peak a p p e a re d a t a l l te m p e ra tu re s. At 100 C and 130 C e x p e rim e n ts w ere sim p ly f in i s h e d a t t h i s tr a n s p a s s iv e p o t e n t i a l, h e n c e, one can e x p e c t s im i la r b e h a v io r o f se c o n d a ry p a s s iv a t io n, th e n,o x y g e n e v o lu tio n upon in c r e a s in g p o t e n t i a l, a s was found a t 200 and 250 C, P o t e n t i a l f o r th e s h a rp tr a n s p a s s iv e peak was ii.c r e a s e d a b o u t 300 mv v /ith in c r e a s in g te m p e ra tu re from 100 to 230 C. I n c r e a s in g te m p e ra tu re from 100 to 230 C a ls o d e c re a s e d th e p o t e n t i a l a b o u t 200 mv f o r c a th o d ic r e a c tio n o f oxygen on Type 304 s t a i n l e s s s t e e l. About 1 decade in c r e a s e i n l i m i t i n g c u r r e n t d e n s ity was o b se rv e d v /ith te m p e ra tu re change from 100 to 230 C due to th e in c r e a s e i n d if f u s io n r a t e o f oxygen i n th e s o lu tio n w ith te m p e r a tu re.

163 144 : U n lik e th e p re v io u s r e s u l t s w ith n o b le m e ta ls a t room te m p e ra tu re re a s o n a b ly l i n e a r T a fe l s lo p e was o b ta in e d a t room te m p e ra tu re and 100 C w ith th e f i r s t s c a n. At te m p e ra tu re s above 100 C b ack scan m ethod was a p p lie d f o r th e s tu d y b e c a u se o f th e n o n lin e a r T a f e l s lo p e vn.th th e f i r s t s c a n, E f f e c t o f Oxygen F ig u re 80 shov/s th e e f f e c t o f d is s o lv e d oxygen on th e p o l a r i z a t i o n c u rv e s o f Type 304 s t a i n l e s s s t e e l in N sodium s u l f a t e s o lu ti o n a t 230 C. I n c r e a s in g oxygen c o n c e n tr a tio n s h i f t e d th e open c i r c u i t p o t e n t i a l to n o b le d i r e c t i o n and c a th o d ic r e a c tio n was r e p la c e d from h ydrogen e v o lu tio n to oxygen r e d u c t io n r e a c t i o n. L im itin g c u r r e n t d e n s ity o f oxygen r e d u c t io n r e a c tio n in c r e a s e d w ith in c r e a s in g oxygen c o n c e n tr a t io n. S in c e o v e ra ll.' an o d ic p o l a r i s a t i o n was n o t a f f e c t e d by oxygen c o n c e n tr a tio n, c a th o d ic and an o d ic p o l a r i z a t i o n curv e co u ld be s e p a r a te d and F ig u re 81 shows th e r e s u l t. A nodic and c a th o d ic p o l a r i z a t i o n c u rv e s i n o x y g en a ted 0.1 N sodium s u l f a t e a t te m p e ra tu re s 100 to 230 C a r e shown in F ig u re s 82 to 83. F or th e c a th o d ic p o l a r i z a t i o n s i n 0.1 N sodium s u l f a t e w ith v a r io u s c o n c e n tr a tio n s o f d is s o lv e d oxygen r e f r e s h e d a u to c la v e sy stem w. s em ployed. D is so lv e d oxygen c o n c e n tr a tio n was a n a ly z e d w ith C h em etrics t e s t k i t. S in c e oxygen consum ption was found i n a way s i m i l a r to t h a t in p u re w a te r, o u t l e t c o n c e n tr a tio n o f oxygen was re g a rd e d a s th e t r u e oxygen c o n c e n tr a tio n in th e a u to c la v e ( s e c t io n 3.5 * 3 ). A f te r oxygen c o n c e n tr a tio n

164 was c o n t r o lle d i n th e fe e d ta n k h ig h p r e s s u r e pump s t a r t e d pumping th e s o lu ti o n and a u to c la v e was h e a te d to 100 C. The o u t l e t s tre a m o f oxygen c o n c e n tr a tio n was o c c a s i o n a ll y m easured to c o n firm th e s te a d y s t a t e oxygen c o n c e n tr a tio n in s id e th e a u to c la v e. M eantim e, c o rro s io n 145 : p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l was m o n ito re d w ith p o t e n t i o s t a t. A f te r s te a d y s t a t e oxygen c o n c e n tr a tio n was o b s e rv e d c o r r o s io n p o t e n t i a l v/as m o n ito re d fo r a n o th e r h o u r, th e n p l o a r i z a t i o n s t a r t e d. S am pling f o r th e oxygen a n a ly s is was made when th e c a th o d ic p o l a r i z a t i o n e x h ib ite d d if f u s io n c o n t r o lle d p r o c e s s. A fte r th e p o la r iz a t io n s tu d y a t 100 C te m p e ra tu re was in c r e a s e d to th e su b se q u e n t h ig h e r te m p e ra tu re. C o rro s io n p o t e n t i a l was m o n ito re d fo r an h o u r b e fo re s t a r t i n g p o l a r i z a t i o n s tu d y a t t h i s te m p e ra tu re. U n lik e th e r e s u l t s vri.th in d i v id u a l e x p e rim en t l i n e a r T a f e l s lo p e was o b s e rv e d i n th e f i r s t s can w ith t h i s m ethod. The r e p r o d u c i b i l i t y o f T a fe l s lo p e a t te m p e ra tu re s 100 to 230 C was exam ined i n 0.1 N sodium s u l f a t e s o lu ti o n w ith 8 ppm oxygen. The v a lu e s o f T a fe l s lo p e, ta b u la t e d i n T a b le 6, was r e p r o d u c ib le w ith in ±20 mv. The d o tte d l i n e i n th e f ig u r e s e x p re s s th e e x t r a p o la t io n o f e x p e rim e n ta l v a lu e s. 7,3.6 C u rre n t Decay E x perim ent C u rre n t decay s tu d y u n d e r c o n t r o lle d p o t e n t i a l was made i n d e a e ra te d 0.1 and 0.01 N sodd.um s u l f a t e s o lu ti o n s a t 250 C, r e s p e c t i v e l y. The e x p e rim e n ts w ere c o n tin u e d f o r 1,000 m in u te s. F ig u re 86 shows th e r e s u l t s in 0,1 N sodium s u l f a t e mvy i s th e p o t e n t i a l f o r sm all

165 146 a c tiv e peak j u s t above c o rro s io n, p o t e n t i a l. The a l lo y was f u l l y p a s s iv a te d a t -200 and s h a rp tr a n s p a s s iv e peak a p p e a re d a t 0 mv^. -yo mvg i s th e in te r m e d ia te p o t e n t i a l f o r p a s s iv e to tr a n s p a s s iv e t r a n s i t i o n. At +300 mvg se c o n d a ry p a s s iv a t io n was o b ta in e d. P o te n t ia l f o r th e o n s e t o f oxygen e v o lu tio n i s +300 mvg. At th e p o t e n t i a l s i n s ta b l e p a s s iv e zone a b o u t 1 decade d e c re a s e in c u r r e n t d e n s ity was o b s e rv e d f o r e v e ry 2 decade change in tim e. The c u r r e n t d e n s ity was a b o u t 1 to 0,5 ua/cm^ a f t e r 1,000 m in u te s. The c u r r e n t v e r s u s tim e cu rv e a t 0 mvg showed c u r r e n t maximum a f t e r 100 m in u te s. V alue o f th e c u r r e n t peak was a b o u t 100 ua/cm^ w hich c o rre s p o n d e d to th e peak i n F ig u re 82. A fte r,\/100 m in u tes c u r r e n t dropped dovm to a p p ro ac h 1 ua/cm^ a f t e r 1,000 m in u te s. At th e in te r m e d ia te p o t e n t i a l f o r p a s s iv e to tr a n s p a s s iv e t r a n s i t i o n (-5 0 mv^j) a s i m i l a r c u r r e n t p eak a p p e a re d a t th e tim e n e a r 1,000 m in u te s. Due to th e o n s e t o f oxygen e v o lu tio n h ig h e s t c u r r e n t d e n s ity was o b s e rv e d a t 500 mvg, An a tte m p t was made to s tu d y th e e f f e c t o f p o t e n t i a l t r a n s i t i o n on c u r r e n t decay b e h a v io r. A fte r th e e x p e rim en t a t 300 mv^, p o t e n t i a l was changed to -500 mv^ and c o rre s p o n d in g c u r r e n t d e c a y b e h a v io r was m o n ito re d, C ath o d ic c u r r e n t was o b se rv e d a t th e i n i t i a l s ta g e o f e x p e rim e n t, th e n c u r r e n t became a n o d ic. A f te r 20 m in u tes o f ex p e rim e n t c u r r e n t rem ain ed unchanged and th e v a lu e was n e a r 1 ua/cm^, Com paring t h i s c u r r e n t d e n s ity w ith t h a t a t mvg. a p p e a re d n e a rly same v a lu e. F ig u re 8? shov;s th e c u r r e n t decay b e h a v io r o f Type 304 s t a i n l e s s s t e e l i n 0,01 W sodium

166 s u l f a t e a t 250 G, 100 mvg i n 0,01 N sodium s u l f a t e i s th e p o t e n t i a l o f s h a rp tr a n s p a s s iv e p eak. The c u r r e n t maximum was a ls o o b s e rv e d a t t h i s p o t e n t i a l and m ost o f p a s s iv e c u r r e n t d e n s it ie s a p p ro a c h e d -^1 ua/cm^ w ith tim e. C om parison o f F ig u re 8? to F ig u re 86 shows n o t much e f f e c t o f s u l f a t e c o n c e n tr a tio n on an o d ic c u r r e n t decay b e h a v io r o f Type 304 s t a i n l e s s s t e e l a t 250 C. 147

167 148 ; 7.4 Discussion E f f e c t o f S u lf a t e ; L i t e r a t u r e S urvey F ig u re 88 and 89 shov; th e p o te n tia l- p H r e l a t i o n s h i p o f s u lp h u r - w a te r sy stem a t 200 and 300 G^^ ^ S u lf a t e i s therm o d y n a m ic a lly s t a b l e i n a "wide re g io n o f aqueous s o l u t i o n s, b u t below l i n e 10 and 11 on th e diagram s s u l f a t e can be re d u c e d to HS o r S^ i n n e u t r a l and a l k a l i n e ph. At room te m p e ra tu re i t was found t h a t s u l f a t e was p r a c t i c a l l y s t a b l e even below th e l i n e s b ec a u se th e r e a c tio n s w ere h ig h ly i r r e v e r s i b l e. S u lf a t e i s re g a rd e d to be i n a c t i v e and i n e r t a t room tem perature^*^^^ However, v e ry l i t t l e in fo rm a tio n i s a v a ila b l e f o r th e s t a b i l i t y o f s u l f a t e a t h ig h te m p e ra tu re s.c o h e n c a lc u la te d th e e f f e c t o f s u l f a t e on ph a t 273 C ( F ig u re 9 0 ). I n c r e a s in g s u l f a t e c o n c e n tr a tio n s h i f t s th e ph o f th e s o lu tio n to h ig h e r value^ ^^ B ie r n a t and R obins c o n s tr u c te d Fe-S-H^O system a t te m p eratu res 25 to F ig ures 91 and 92 a r e th e r e s u l t s a t 200 and 300 C, r e s p e c t i v e l y. At p o te n t i a l s below mvjj FeS^ o r FeS r e p la c e d th e s t a b l e zone o f m a g n e tite a t ph 7. C o n seq u e n tly, s t a b l e domain o f m a g n e tite v i r t u a l l y d is a p p e a re d a t t h i s ph. Above th e p o t e n t i a l h e m a tite was s t i l l s t a b l e. S im ila r tr e n d was o b ta in e d a t lo w e r te m p e r a tu r e s, A number o f i n v e s t i g a tio n s have been made f o r s tu d y in g th e p a s s iv a t io n b e h a v io r o f ir o n i n v a r io u s c o n c e n tr a tio n s and p H 's o f sulfate^s m ialow ska and Mrowczynski^^*^^ have s tu d ie d th e p a s s iv a t io n b e h a v io r o f ir o n i n d e a e ra te d 0.1 N sodium s u l f a t e s o lu ti o n. They have p o s tu la te d t h a t tv;o ty p e s o f film s form i n th e s u l f a t e sy stem ; nonp r o t e c t i v e l i n e a r l y grow ing s a l t f ilm s (FeS0^, 7H20),

168 and p r o t e c t i v e, lo g a r ith m ic a l ly grow ing o x id e f ilm s, d ep endin g upon th e p o t e n t i a l o f th e sy stem. Below 500 mvjj form er film was found to be s t a b l e and above th e 149 p o t e n t i a l l a t t e r was th e s t a b l e f ilm. For th e s a l t film fo rm a tio n th e fo llo w in g r e a c tio n s v/ere p ro p o se d by Economy o t. a l ( ^ ^ ) Fe(OH)^= Fe^'*'+ 20H" Fe^'*'+ S0^ + YHgO = FeSO.yn^O S in c e th e q u e s tio n a b le e f f e c t o f s u l f a t e on e l e c t r o ch e m ic a l b e h a v io r o f Type 304 s t a i n l e s s s t e e l, th r e e d i f f e r e n t c o n c e n tr a tio n s o f s u l f a t e (0,1-0,0 0 1 ) w ere chosen f o r th e p r e s e n t s tu d y C a lc u la tio n s o f ph a t v a r io u s c o n c e n tr a tio n s o f s u l f a t e a t te m p e r a tu re s betw een 100 and 300 C The Conen s m ethod was a d o p te d h e re f o r th e c a l c u l a t i o n s. A b r i e f d e s c r i p tio n o f th e c a l c u la tio n s i s th e f o llo w in g, A s tu d y o f th e e l e c t r o l y t i c p r o p e r t ie s o f sodium s u l f a t e r e v e a le d t h a t i n w a te r a t 250-3?0 C t h i s compound i s p a r t i a l l y i n an a s s o c ia te d s t a t e (a s th e in te r m e d ia te io n NaSO]^) and p a r t i a l l y i n a 'h y d r o ly s e d s t a t e due to r e a c t i o n o f th e SO^ io n s w ith th e io n s o f w a te r and fo rm a tio n o f a w eaker e l e c t r o l y t e ( th e b i s u l f a t e io n ' HSO^), w ith a c o rre s p o n d in g change in th e r e a c t i o n o f th e medium. The r e s u l t i n g e q u a tio n i s th e fo llo w in g, Na'^ + NaSO: + H.O Ha + SO, = d H + OH" I

169 150 But d i s s o c ia tio n c o n s ta n t o f HSO^ io n i s s e v e r a l o r d e rs lo w e r th a n th e d i s s o c ia tio.uxi n cuuxiü o n s UdXiU ta n t UJ. o f th UU55 e NaSO% i'ido Uf -LUU io n u n d e r th e same c o n d itio n ( C ) /^ ^ ) At 343 C (650 F ) gives only 0.1 ph u n it c o rre c tio n due to NaSO^ a s s o c ia tio n ^ M a rs h a ll and Jones^ ' d e te rm in e d th e v a lu e s f o r th e seco n d d i s s o c i a t i o n c o n s ta n t o f H^SO^ ( i. e. HSO^ = H ^+ s o p from e x te n s iv e s o l u b i l i t y measure-», m ents o f CaSO^ and i t s h y d ra te s i n aqueous s u l f u r i c a c id a t te m p e ra tu re s from 25 to 350 C, The r e s u l t i n g e q u a tio n i s, lo g Kd = logt - w here Kd = ) (SO^) ^ i n k (HSOp C obble^^^^ d e te rm in e d th e e q u a tio n f o r (H"*") by s o lv in g th e th r e e s im u lta n e o u s e q u a tio n s r e s u l t i n g from th e d i s s o c ia tio n o f w a te r, th e mass b a la n c e e q u a tio n f o r s u l f u r : th e n. HgO = H'^+ 0H th e d i s s o c ia tio n o f HSO^ and K^= (H ^)(OH") ESOT= + SOT Kd= (B'*')(SOp Co = (HSOp + ( s o p (H+) =, Kw(Kd + (H + ))p Kd + Co +(H+) (HSOp The r e s u l t s fo r th e ph c a lc u la tio n s a r e shown i n T a b le 7 and F ig ure 96. T

170 151 CM OJ r A [>. VO LT\ LT\ c n ' - l A 0 0 \ r A - - A A N d i r u r l O ' O ' - d - M D D - c o l > - M D V D V D V O V D V O V O l> - C7\ A VO O O f A A CO VD CM v d v o a a a v o v o m d _d- CO oo VO l>- _ j - CM ( A r A G \ A A A CM CM CM A

171 7.4.3 Effect of Sulfate; Experimental 152 E f f e c t o f s u l f a t e io n c o n c e n tr a tio n on th e c o r ro s io n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l a t 230 C i s shown i n F ig u re 103. S in c e th e p o t e n t i a l s were m o n ito re d f o r an h o u r b e fo re p o l a r i z a t i o n s tu d y, th e v a lu e s do n o t r e p r e s e n t tr u e s te a d y s t a t e p o t e n t i a l. Hovfever, t h i s f ig u r e shows t h a t in c r e a s in g s u l f a t e d e c re a s e d th e c o rro s io n p o t e n t i a l i n b o th o x y g en ated and d eoxygenated w a te r. B ecause p a s s iv e c u r r e n t d e n s ity o f Type 304 s t a i n l e s s s t e e l was n o t a f f e c te d by s u l f a t e c o n c e n tr a tio n, th e d e c re a s e in c o rro s io n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l w ith s u l f a t e i s r a t h e r r e l a t e d to th e p o t e n t i a l drop o f r e d u c tio n k i n e t i c s o f oxygen, o r p o s s ib ly t h a t - o f w ate r in d e a e ra te d s o lu tio n ( F ig u r e 73 and 7 5 ). F ig u re 4 shows t h a t in c r e a s in g ph d e c re a s e s th e e q u ilib riu m p o t e n t i a l s o f oxygen e l e c tr o d e and hydrogen e l e c tr o d e. H ence, th e d e c re a s e i n p o t e n t i a l o f re d u c tio n k i n e t i c s w ith s u l f a t e c o n c e n tr a tio n can be e x p la in e d by th e change in ph w ith s u l f a t e. The d e c re a s in g tr e n d o f th e p o t e n t i a l o f tr a n s p a s s iv e peak w ith in c r e a s in g s u l f a t e can a ls o be e x p la in e d by th e ph change o f th e s o lu ti o n v ;ith s u l f a t e, s in c e th e peak was found to be a s s o c ia te d w ith th e d i s s o lu ti o n o f chromium o x id e ( s e c t io n ) o f w hich e q u ilib riu m p o t e n t i a l d e c re a s e d w ith in c r e a s in g ph (F ig u re 4 ). The c o n c e n tr a tio n s o f s u lf u r and oxygen p r o f i l e in th e o x id e f ilm, form ed a n o d ic a lly a t 0 mvjj ( th e tra n sp a ss iv < peak p o t e n t i a l ) i n 0,1 N sodium s u l f a t e, i s shown in F ig u re 93. G e n e ra lly, 1 m inute s p u tte r in g tim e c o rre s p o n d s to 5 A th ic k n e s s o f o x id e film. N o tic e t h a t d i f f e r e n t s c a l e s w ere u se d f o r oxygen and s u l f u r. As film was rem oved, b o th s u l f u r and oxygen c o n c e n tr a tio n s showed

172 153 d e c re a s in g tr e n d. B ased on t h i s o b s e r v a tio n i t can be co n c lu d e d t h a t s u l f u r i n th e film came from th e s o lu ti o n, T r a n s p a s s iv e peak One o f th e m ost s i g n i f i c a n t o b s e r v a tio n on th e an o d ic p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l i s th e e x is te n c e o f s h a rp tr a n s p a s s iv e p eak. S in c e th e p o t e n t i a l s o f th e p eak a t v a r io u s te m p e ra tu re s a r e c lo s e to th e e q u i l i brium p o t e n t i a l o f Crof'/Cr^O^ r e a c t i o n (F ig u re 1 to 4 ), th e p eak can be r e l a t e d to th e d is s o lu ti o n o f chromium o x id e to form ch ro m âte. The e x p e rim e n ta l r e s u l t s o f c u r r e n t decay e x p e rim en t a t th e p o t e n t i a l o f t h i s peak i n F ig u re s 86 and 87 a p p e a r th e c u r r e n t maxima, o f v;hich v a lu e s a r e c lo s e to th e peak c u r r e n t s o f th e p o l a r i z a t i o n c u rv e s. A f te r th e c u r r e n t maxima c u r r e n t s d ropped down to a p p ro ac h th e s t a b l e p a s s iv e c u r r e n t. An a tte m p t was made to a n a ly z e th e s u r f a c e c o m p o sitio n o f th e specim en w itl: A uger e l e c tr o n s p e c tro s c o p y (AES), The r e s u l t i n F ig u re 94 show no chromium c o n te n t in th e f ilm. B ased on th e e x p e rim e n ta l o b s e r v a tio n s and therm o dynam ic c a l c u l a t i o n i t can be s t a t e d t h a t th e s h a rp tr a n s p a s s iv e pealc i s r e s u l t e d from th e d i s s o l u t i o n o f chromium o x id e to form chro m âte. A f te r th e c u r r e n t maxima, i n th e F ig u re s 86 and 87, s u r f a c e o f th e m e ta l h as v i r t u a l l y no chromium b ec a u se o f th e f a s t e r d is s o lu tio n r a t e o f chromium o x id e th a n th e su p p ly o f chromium by th e d if f u s io n o f th e s p e c ie in th e m e ta l m a tr ix. I n i t i a l d e c re a s e in c u r r e n t a t th e p o t e n t i a l may have been a s s o c ia te d w ith th e fo rm a tio n o f o x id e f ilm and th e o x id e s t a r t e d d is s o lv in g w ith in c r e a s in g c u r r e n t. In F ig u re 76 no tr a n s p a s s iv e p eak a p p e a re d upon r e v e r s e s can b e c a u se o f th e ab sen ce o f chromium on th e s u r f a c e. Lower p a s s iv e c u r r e n t d e n s ity on r e v e r s e scan may be e i t h e r due to th e r e d e p o s i tio n o f chromium on th e s u r f a c e o r th e p r o te c ti v e n e s s o f th e

173 1 5 4 p a s s iv e f ilm w ith o u t chromium o x id e on th e s u r f a c e. Long te rm c u r r e n t decay ex p e rim e n t a t mvg a f t e r th e t e s t s a t +300 mvjj i n 0.1 N sodium s u l f a t e and +100 mvg i n 0,01 N so'dium s u l f a t e, r e s p e c t i v e l y, showed same v a lu e s o f c u r r e n t d e n s ity a s th o s e a t -500 mvg, T h is i n d i c a t e s t h a t th e p a s s iv e c u r r e n t d e n s ity o f th e p o l a r i z a t i o n c u rv e w ith r e v e r s e s can approaches th e valu e v /ith forw ard scan a f t e r a lo ng tim e, E s tim a tio n o f E le c tro c h e m ic a l P a ra m e te rs o f Oxygen R e d u c tio n K in e tic s r e a c t i o n, B ased on th e e x p e rim e n ta l r e s u l t s o f oxygen r e d u c tio n O2 + 4H'^ + 4e = REgO (7-1 ) ' im p o rta n t e le c tr o c h e m ic a l p a ra m e te rs w ere e s tim a te d and ta b u la t e d i n T a b le 8. F or a c t i v a t i o n c o n t r o lle d r e a c tio n th e r a t e e q u a tio n i s g iv e n by, K ( a o ^ ) ^ ( a ^ t) y e x p ( S ^ ) e x p ( - ^ t1 -g? g E ) (7-2 ) From e q u a tio n 7-2 th e p ro d u c t, z (l-o O can be c a lc u la te d from T a f e l s lo p e o f th e p o l a r i z a t i o n c u rv e a t each te m p.. A ssum ing i s?, i t was fo u n d t h a t number o f e l e c tr o n s a t th e r a t e d e te rm in in g s te p v/as a b o u t 1, Exchange c u r r e n t '.a. d e n s i t i e s w ere d e te rm in e d by e x t r a p o la t in g th e c a th o d ic c u r r e n t d e n s i t i e s to th e therm odynam ic e q u ilib r iu m p o te n t i a l s, F or th e c a l c u l a t i o n s o f e q u ilib r iu m p o t e n t i a l s o f oxygen e l e c tr o d e a t d i f f e r e n t oxygen c o n c e n tr a tio n s (A ppendix A) ph o f th e s o l u t i o n a t v a r io u s c o n c e n tr a tio n s. o f s u l f a t e io n was ta k e n from t a b l e 7, The p a r t i a l d e r i v a t iv e o f lo g i ^ w. r. t, lo g aq^ i s th e r e a c t i o n o r d e r x. The v a lu e s a p p e a re d to be? to 1, About 4,0 0 0 c a l/m o l o f a c t i v a t i o n en e rg y f o r th e oxygen r e d u c tio n r e a c tio n was o b ta in e d by th e A rrh e n iu s p l o t, lo g i_ v s, l/t ( F ig u r e 9 7 ),

174 155 i s, For d if f u s io n c o n t r o lle d r e a c tio n th e r a t e e q u a tio n i l = ^^^02^02 (7-3 ) From th e l i m i t i n g c u r r e n t d e n s i t i e s i n c a th o d ic p o la r iz a t io n c u rv e s th e r a t i o, Dq, can be e s tim a te d. S in c e th e d i f f u s i v i t y o f oxygen i s g iv e n by(8 4 ) where = 8.03 x 10 '^ cm ^ /sec. = 3,490 cal/m o le s e p a r a te d v a lu e s o f Dq^ and ^ were o b ta in e d. Assuming p a s s iv e c u r r e n t d e n s ity b e in g 1 ua/cm^, one can e s tim a te th e.lo w e s t c o n c e n tr a tio n o f oxygen in w ate r f o r a c t i v a t i o n c o n t r o lle d r e a c tio n and th e v a lu e v/as about 10 ppb o f oxygen a t 250 C, From th is c a lc u la tio n i t can be c o n c lu d ed t h a t oxygen re d u c tio n r e a c tio n in h ig h te m p e ra tu re w ate r i s m o s tly a c t i v a t i o n c o n t r o lle d.

175 A H y p o th e tic a l P o la r i z a t io n Curve i n W ater a t 2.30 C B ased on th e e x p e rim e n ta l o b s e rv a tio n s in v a rio u s c o n c e n tr a tio n s o f s u l f a t e a t 250 C an a tte m p t was made to e x t r a p o la t e th e r e s u l t s to z e ro c o n c e n tr a tio n o f s u l f a t é. The r e s u l t i s shown i n F ig u re 95. Assuming s u l f a t e a f f e c t s o n ly ph o f th e s o lu ti o n (F ig u re -90) th e p o t e n t i a l s o f th e c u r r e n t peak (C r0^ " /C r 2 0..,..re a c tio n ) and oxygen e v o lu tio n r e a c tio n w ere re a s s ig n e d on th e b a s is o f therm odynam ic c a lc u la tio n s (F ig u re 4) and th e g e n e ra l shape o f th e p o l a r i z a t i o n cu rv e in th e concent r a t i o n ra n g e s ( IN) o f sodium s u l f a t e. C o rro sio n p o t e n t i a l o f Type 304 s t a i n l e s s s t e e l in p ure v /a ter was tal^en from F ig u re 15. S teady s t a t e p o la r iz a t io n curve was c o n s tr u c te d w ith th e r e s u l t s o f c u r r e n t decay e x p e rim ent. C ath o d ic p o l a r i z a t i o n c u rv e s o f oxygen r e d u c tio n r e a c tio n wore d ete rm in e d by assum ing T a fe l s lo p e and l i m i t i n g c u r r e n t d e n s i t i e s re m a in in g u n a f f e c te d by s u l f a t e. The p o t e n t i a l s o f c a th o d ic p o la r iz a t io n c u rv e s w ere a s s ig n e d b ased on th e v a lu e s o f c o rro s io n p o t e n t i a l s i n F ig u re 15. S in ce th e c u r r e n t peaic in th e f ig u r e v/as found to be t r a n s i e n t, no peak was in c lu d e d in th e s te a d y s t a t e p o l a r i z a t i o n cu rv e.. A boverj+300 mv^^ o x id e on th e m e ta l h as v i r t u a l l y no chromium in s te a d y s t a t e p o la r iz a t io n cu rve, though th e curve does no t show such a tr a n s itio n. At th e oxygon c o n c e n tr a tio n s above 1 ppm s u r f a c e film o f Type 304 s t a i n l e s s s t e e l may be r e l a t i v e l y u n s ta b le due to th e p o s s ib le d is s o lu tio n o f chromium o x id e.

176 /fi7 Comparison o f P resen t Study v /ith th a t R eported in L i t e r a t u r e. A com parable s tu d y, shown i n F ig u re 9% was made by F u j i i e t. They u s e d e x t e r n a l r e f e r e n c e e le c tr o d e f o r th e i n v e s t i g a t i o n o f p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l i n h ig h te m p e ra tu re o x y g en a ted w a te r. Scan r a t e v/as 30 mv/min. and 0.1 N sodium s u l f a t e was th e s u p p o rtin g e l e c t r o l y t e. A lthough d i r e c t com pariso n o f th e e l e c tr o d e p o t e n t i a l betw een two s tu d ie s i s n o t p o s s i b le, good c o r r e l a ti o n was o b s e rv e d betw een t h e i r r e s u l t s and p r e s e n t s tu d y. They o b se rv e d tr a n s p a s s iv e b e h a v io r o f an o d ic p o l a r i z a t i o n c u rv e a t th e p o t e n t i a l above 7OO mv from th e c o r r o s io n p o t e n t i a l o f th e a l lo y in d e a e ra te d s o lu ti o n. P o la r i z a t io n c u rv e s in o x y g en a ted w a te r a ls o showed r e a s o n a b le ag reem en t betw een two s tu d ie s (F ig u re 80 and 98). S in c e th e y u se d f a s t e r sc a n r a t e, g e n e ra lly h ig h e r c u r r e n t d e n s ity was o b ta in e d r e s u l t s. i n. t h e i r A nother com parable s tu d y v;as made by In d ig et.al^if"^^ F ig u re s 99 and 100^how th e r e s u l t s. They u sed Ag/AgCl r e f e r e n c e e l e c tr o d e f o r th e p o l a r i z a t i o n s tu d y o f Type 304 s t a i n l e s s s t e e l in 0.01 W sodium s u l f a t e a t 274 C. Scan r a t e was 3 m V /second. U n lik e th e r e s u l t s o f p r e s e n t s tu d y, th e y d id n o t o b serv e tr a n s p a s s iv e peak upon an o d ic p o l a r i z a tio n in F ig u re 100, w hereas i n F ig u re 99 in c r e a s e d c u r r e n t was o b s e s e rv e d a t 100 mvg. T h is tr a n s p a s s iv e b e h a v io r was d is a p p e a re d a f t e r re p e a te d ru n. The a b sen ce o f d i s t i n c t tr a n s p a s s iv e b e h a v io r i n t h e i r r e s u l t s may be due to th e f a s t s can r a t e, a s was o b s e rv e d i n th e p r e s e n t s tu d y and th e r e s u l t s by H uebner a t. a l. (F ig u re s 7 I and? 2 ).

177 7.5 Summary of Experimental Results 1) E f f e c t o f s u l f a t e io n on th e a n o d ic p o l a r i z a t i o n b e h a v io r o f Type 304 s t a i n l e s s s t e e l was n o t s i g n i f i c a n t. 2) I n c r e a s in g s u l f a t e c o n c e n tr a tio n d rc re a s e d th e p o t e n t i a l o f oxygen r e d u c tio n r e a c t i o n a t 250 C, p o s s ib ly due to th e in c r e a s e i n ph v jith s u l f a t e a d d i tio n. 3) The c o n c e n tr a tio n o f h ydrogen p e ro x id e form ed a s an in te r m e d ia te com plex o f oxygen r e d u c tio n r e a c tio n m ark ed ly a f f e c te d th e c a th o d ic p o l a r i z a t i o n cu rv e i n o x y g e n a te d w a te r. At open c i r c u i t p o t e n t i a l 50 ppb o f p e ro x id e was d e te c te d i n 0.1 N sodium s u l f a t e s o lu ti o n a t 250 C. I n c r e a s in g c o n c e n tr a tio n o f p e ro x id e a p p e a re d a f t e r c a th o d ic p o l a r i z a t i o n. 4 ) Due to th e b u ild up o f p e ro x id e c o n c e n tr a tio n d u rin g p o l a r i z a t i o n d i s t i n c t T a f e l s lo p e o f oxygen re d u c tio n r e a c tio n was o b ta in e d upon r e v e r s e s c a n. 5) I n c r e a s in g te m p e ra tu re, in c r e a s e d th e p a s s iv e c u r r e n t d e n s ity o f anodic p o l a r i z a t i o n c u r v e, d e c re a s e d th e p o t e n t i a l o f c a th o d ic r e a c tio n and in c r e a s e d th e l i m i t i n g c u r r e n t d e n s ity o f oxygen r e d u c tio n r e a c t i o n. 6) E a s te r s c a n r a t e showed h ig h e r p a s s iv e c u r r e n t d e n s ity i n a n o d ic p o l a r i z a t i o n c u rv e, w h ereas n o t much change was o b s e rv e d i n c a th o d ic p a r t o f th e p o l a r i z a t i o n c u r v e. 7) S h arp tr a n s p a s s iv e peak i n an o d ic p o l a r i z a t i o n cu rv e was a s s o c ia te d v /ith th e d i s s o l u t i o n o f chromium o x id e to form ch ro m âte. C u rre n t decay ex p erim en t, showed t h a t th e p eak was t r a n s i e n t.

178 159 8) C u rre n t decay e x p e rim e n t i n 0.1 an d 0,01 N sodium s u l f a t e s o lu ti o n c o n firm e d no s i g n i f i c a n t e f f e c t o f s u l f a t e c o n c e n tr a tio n on a n o d ic k i n e t i c s o f Type 30k s t a i n l e s s s t e e l a t 2$0 C. 9) S u lf u r v/as d e te c te d i n o x id e film form ed an o d ic a l l y i n 0.1 N sodium s u l f a t e a t 250 C by AES, D ecrea sin g s u l f u r c o n te n t w ith th e rem o v al o f o x id e la y e r in d i c a t e d t h a t s u l f u r came from th e s o lu ti o n. 10) B ased on th e e x p e rim e n ta l o b s e r v a tio n o f oxygen re d u c t i o n k i n e t i c s j im p o rta n t e le c tr o c h e m ic a l p a ra m e te rs w ere e s tim a te d. Above 10 ppb o f oxygen i n v /a ter a t 250 C th e r e d u c tio n k i n e t i c s o f oxygen w ere a c t i v a t i o n c o n t r o l l e d. 11) P o l a r i z a t i o n cu rv e o f Type 30k s t a i n l e s s s t e e l in p u re w a te r a t 2 ^ 0 was c o n s tr u c te d by e x t r a p o la t in g th e e x p e rim e n ta l r e s u l t s.

179 7.6 S uggestions fo r F u tu re Work 160 i E xtension o f C urrent Decay E xperim ent; The U sef o f AES and SEM A n a ly s is o f s u r f a c e c o m p o sitio n w ith AES (o r ESCA) and m orphology o f o x id e film w ith SEM a f t e r c u r r e n t decay ex p e rim en t p ro v id e u s e f u l in f o r m a tio n f o r u n d e rs ta n d in g th e c o rro s io n b e h a v io r o f a l lo y s i n aqueous s o l u t i o n s. H ence, s u r f a c e c o m p o s itio n. o f one specim en a f t e r 1000 m in u tes ex p o su re i n 0.1 N sodium s u l f a t e a t 2$0 C was s tu d ie d w ith AES, A p p lie d p o t e n t i a l f o r th e specim en was 0 mvxj v;hich was th e tra n sp a ss iv e peak p o te n tia l. The r e s u lts fo r S, 0 and Cr were shoivn in F ig ure 93 and ' 94, r e s p e c t iv e l y. The c o n c e n tr a tio n p r o f i l e o f n ic k e l was a ls o a n a ly z e d and shov/n i n F ig u re 104. E nrichm ent o f n ic k e l was o b se rv e d in th e f ig u r e, p o s s ib ly due to e i t h e r r e d e p o s itio n o f n ic k e l s a l t d u rin g c o o lin g p e r io d o r h ig h e r s o l u b i l i t y o f i r o n o x id e. For b e t t e r u n d e rs ta n d in g o f t h i s phenomenon f u r th e r in v e s t i g a t i o n i s n e c e s s a r y. O xide s u r f a c e was a ls o i n v e s t i g a t e d w ith SEM. F ig u re 101 and 102;shov/ th e s u r f a c e m orphology o f th e specim ens a f t e r th e c u r r e n t decay e x p e rim en t a t th e p o t e n t i a l o f tr a n s p a s s iv e peak i n 0.1 and 0,0 1 N sodium s u l f a t e, re s p e c t i v e l y, T hick o x id e film was o b s e rv e d v ;ith th e specim en in 0,01 N sodium s u l f a t e, w hereas s a l t d e p o s it seem ed to be found in 0,1 N sodium s u l f a t e. T h is s a l t d e p o s it, p o s s ib ly ir o n o r n ic k e l s u l f a t e, may have r e s u l t e d from th e r e d e p o s itio n o f c o r r o s io n p ro d u c t on th e specim en d u rin g c o o lin g p e rio d due to th e s o l u b i l i t y l i m i t. O xide film o f th e specim en a f t e r 200 h o u rs e x p o su re i n p u re w ate r w ith 8 ppm oxygen c o n c e n tr a tio n a t 2$0 C

180 was a ls o in v e s t ig a t e d w ith SEM f o r th e p u rp o se o f comp a r is o n w ith th o s e i n sodium s u l f a t e (F ig u re IO4 ). U n lik e th e s u r f a c e m o rp h o lo g ies o f specim ens in F ig u re s.161; 101 and 102, no p a r t i c u l a r c o r r o s io n p ro d u c t a p p e a re d on th e s u r f a c e o f specim en i n F ig u re 103'.'. T h is o b s e r v a tio n s u g g e s ts t h a t p o t e n t i a l o f th e specim en in p u re w a te r w ith 8 ppm oxygen a t 250 C may s t i l l l i e below th e t r a n s p a s s iv e p o t e n t i a l (F ig u re 9 3 ). For f u r th e r i n v e s t i g a t i o n s o f a n o d ic a lly form ed o x id e film w ith AES and SEM, specim ens a t d i f f e r e n t p o t e n t i a l s i n 0,01 N sodium s u l f a t e a t 250 C were c o l l e c t e d. But u n f o r tu n a te ly, due to th e m a lfu n c tio n o f in s tr u m e n ts th e i n v e s t i g a t i o n was n o t co m p leted. S in c e th e s tu d y o f o x id e film form ed in h ig h te m p e ra tu re w a te r i s e s s e n t i a l, c o n tin u a tio n o f t h i s e x p e rim en t i s s u g g e s te d. A uthor a ls o s u g g e s ts to e x te n d t h i s ty p e o f ex p e rim en t to o th e r a llo y s, such as In c o n e l 600 and In c o lo y , 6,2 D evelopm ent o f Im proved R e fe re n c e E le c tro d e and Working E lectro d e H older Ag/AgCl e l e c tr o d e i s one o f th e most common i n t e r n a l r e f e r e n c e e le c tr o d e f o r th e e le c tr o c h e m ic a l s tu d y o f aqueous c o r ro s io n a t h ig h te m p e ra tu re. A lthough p r e s e n t d e s ig n o f th e re f e r e n c e e le c tr o d e (F ig u re 30) s a t i s f i e d th e re q u ire m e n t o f t h i s s tu d y, an e f f o r t h a s been c o n tin u e d to im prove th e r e l i a b i l i t y and d u r a b i l i t y o f th e e l e c tr o d e. The p re v io u s i n v e s t i g a t i o n encoura g ed th e u se o f z ir c o n ia c o a te d ziro n iu m tu b in g f o r th e e l e c tr o d e cham ber o f th e r e f e r e n c e e l e c tr o d e. T h is s t r u c t u r a l m a te r ia l seem s to be more ad v a n tag eo u s th a n

181 th e T e flo n due to th e s t a b i l i t y o f th e m a te r ia l a t h ig h te m p e ra tu re. For th e p r e s e n t s tu d y T e flo n c o a te d s t a i n l e s s s t e e l v;as u sed as an e le c tr o d e h o ld e r. Ov/ing to th e p h y s ic a l p ro p e rty o f T e flo n th e c o a te d l a y e r was fre q u e n tly damaged. M oreover, t h i s T e flo n c o a te d s t a i n l e s s s t e e l h o ld e r cannot be u sed fo r th e s tu d y a t te m p e r a tu r e s above 280^0 due to th e i n s t a b i l i t y o f T e f lo n. H ence, z i r c o n ia c o a te d z irco n iu m h o ld e r h as been fo c u s e d f o r th e developm ent o f im proved e le c tr o d e h o ld e r. Though i t h as a c e r t a i n l i m i t a t i o n o f a p p l ic a t io n ( i. e. i n s t a b i l i t y o f z i r c o n ia i n th e p re s e n c e o f f lu o r id e io n, e t c. ) th e u s e o f t h i s e le c tr o d e h o ld e r seem s to have a b r ig h t p r o s p e c t.

182 163 F ig u re 68, E le c tro d e arrangem ent f o r P o la r i z a t io n S tudy

183 ' M a te r ia l: Type 3O4 s t a i n l e s s s t e e l Gone, o f Op: A ir S a tu r a te d Cone, o f itapso, T em perature: Room Tem perature Scan Rati mv/200 sec 10 mv/20 s e c. 10 mv/2 s e c j J. ± C u rre n t d e n s it y, ua/cm^ F ig u re 69. E f f e c t o f sc a n r a t e on th e p o l a r i z a t i o n c u rv e o f Type 304 s t a i n l e s s s t e e l a t room te m p e ra tu re

184 165: 1,200 1,000 Temperature Material Solution 250 C Quench Annealed Type Stainless Steel 0.1 N Sodium Sulfate E 200 Current D en sity, /x A /c m F ig u re 70. E f f e c t o f.scan r a t e on th e p o l a r i z a t i o n cu rv e o f Type 304 s t a i n l e s s s t e e l i n 0.1 N sodium s u l f a t e a t 2300c

185 166 1,200 Temperature : 250 C Materiel : Ouencti Annealed Type Stainless 51 Solution : N Sodium Sulfate Current D en sity, /x A /c m ^ F ig u re 71. E f f e c t o f scan r a t e on th e p o l a r i z a t i o n c u rv e o f Type 304 s t a i n l e s s s t e e l in 0.001N sodium s u l f a t e a t 2300c

186 800 T em perature: 300 C M a te r ia l: S e n s itiz e d Type 304 s t a i n l e s s s t e e l S o lu tio n : 20 ppm S of" mv/hour 600 mv/hour mv/hour 10 C u rrent D ensity, ua/cm' 100 1,000 F ig u re? 2. E f f e c t o f s can r a t e on p o l a r i z a t i o n b e h a v io r a f t e r H uebner e t. a l. (47)

187 168 : 1,200 Temperature Material Solution Scan Rote 2 50 C Quench Annealed Type Stainless Steel Sodium Sulfate - 20 Minutes at Each Potential > 200 Current D en sity,^ A /c m ^ F ig u re 73, E f f e c t o f s u l f a t e c o n c e n tr a tio n on th e an o d ic p o l a r i s a t i o n cu rv e o f Type 304 s t a i n l e s s s t e e l a t C

188 N E l j i! mo.in Materia!: Quench Annealed 1 } ,000 Temperature: Room Temperature Solution: Air Saturated Sodium Sulfate Scan Rate ' 10 m V /2 0 Seconds Scan Direction: Nobie to Active IN 1, L- -1L-1- III ' Current Density, /xa/cm^ F ig u re 74. E f f e c t o f s u l f a t e c o n c e n tr a tio n on c a th o d ic p o l a r i z a t i o n cu rv e o f Type 304 s t a i n l e s s s t e e l a t room te m p e ra tu re, - -

189 -200 E ,000 Material: Quench Annealed 0.1 N... Temperature : 250 C Solution : Air Saturated Sodium Sulfate Scan Rate: tomv/20seconds Scan Direction: Noble to Active >0.01 N -1,200 L io 10^ Current Density, ^ A /c m ^ F ig u re 75. E f f e c t o f s u l f a t e c o n c e n tr a tio n on c a th o d ic p o l a r i z a t i o n curv e o f Type 304 s t a i n l e s s s t e e l a t 250 C

190 171 I 1,200 1,000 Temperature Material Solution Scan Rate 250 C Quench Annealed Type Stainless Steel 0.0 1N Sodium Sulfate ~ 20 Minutes at Each Potential E 200-1,000 Current D ensity, ^ A /c m ^ Figure 76. Effect of reverse scan on anodic polarization curve of Type 30A stainless steel in 0.01 N sodium sulfate at 250 C

191 E -400 ^ Materia! : Quench Annealed Type 304 Temperature: 25 0 C Solution : O.i N Sodium Sul fate Cone, of O2 7ppm Scon Rote: to m V /20 Seconds I-I I I I... 1I I I I... I 11 L 10'' 10 10' 10^ Current Density, p l\/c r r 7 F ig u re 77. E f f e c t o f r e v e r s e sc a n on c a th o d ic p o l a r i z a t i o n cu rv e o f Type 304 s t a i n l e s s s t e e l i n 0.1 N sodium s u l f a t e a t 230 C

192 m 1,200 Material : Quench Annealed Type 304 Stainless Steel Solution : 0.1 N Sodium Sulfate Scan Rate ~ 20 Minutes at Each Potential E 200 Current D en sity, ^ A /c m * Figure 78. Effect of temperature on anodic polarization curve of Type 304 stainless steel in 0.1 N sodium sulfate

193 200 - I 1 "I" I T I I I C % 0 C Material: Quench Annealed Type 3 04 Stainless Steel Solution: 0.1 N Sodium Sulfate Cone, of O2 : 6 ppm Scon Rote tomv/20seconds Current Density,/xA/cm^ F ig u re 79. E f f e c t o f te m p e ra tu re on c a th o d ic p o l a r i z a t i o n c u rv e o f Type 304 s t a i n l e s s s t e e l i n 0.1 N sodium s u l f a t e

194 175 T ' Temperature : C Material Quench Annealed Type 304 Stainless Steel Solution : 0.0 1N Sodium Sulfate Anodic Scon Rale Minnies of Each Polential Cathodic Scan Rate ' 10 mv/ 20 Seconds O2 0.1 ppm D eaera ted C urrent D e n sity,/x A /c r r 3 F ig u re 80. E f f e c t o f oxygen on p o l a r i z a t i o n c u rv e o f Type 304 s t a i n l e s s s t e e l in 0.01 N s o d iu n s u l f a t e at 230OC

195 -176 T~ Tem perature ; 250 C Material ; Quencti Annealed Type 304 Stainless Steel Solution 0.01 N Sodium Sulfate Anodic Scan Rate : ~ 2 0 Minutes at Each Potential Cathodic Scon Rate : IOmV /20 Seconds 0,: 10 ppm 0, : 2ppm Current D en sity, /j,a /cm ^ Figure 81, Cathodic..and anodic polarization curves of ; Type 302+ stainless steel in oxygenated 0.01 N sodium sulfate solution at 230

196 177 : Temperature : 250 C Material : Quench Annealed Type Stainless Steel Solution 0.1 N Sodium Sulfate Anodic Scan Rate ~ 2 0 Minutes at Each Potential Cathodic Scon Rote : IOmV /20 Seconds Og: 0.6 ppm O; : 8 ppm Current D e n sity,/x A /c m ^ Figure 82» Cathodic and anodic polarization curves of Type 30if stainless steel in oxygenated 0,1 N sodium sulfate solution at 250 C

197 178 : 1,200 Temperate ; 200 C Material : Quench Annealed Type 3 04 Stainless Steel Solution : 0.1N Sodium Sulfate Anodic Scan Rate : ~ 2 0 Minutes at Each Potential Cathodic Scan Rote : IOmV /20 Seconds Og: 0.07 ppm 02:0.8 ppm - 1,000 Current D en sity, /J.A /cm ^ Figure 83. Cathodic and anodic polarization curves of Type 304 stainless steel in oxygenated 0,1 N sodium sulfate solution at 200 C

198 179 1 ^ Temperature M aterial Solution : 0.1N Sodium Sulfate Anodic Scon Rote ~ 2 0 Minutes at Each Potential Cathodic Scon Rote : I50 C : Quench Annealed Type Stainless Steel 10 m V /20 Seconds 0 %: 0 9 ppm ul_ Current D ensity, yu.a/cm^ Figure 3if. Cathodic and anodic polarization curves of Type 304 stainless steel in oxygenated 0,1 N sodium sulfate solution at 150 G

199 1.80! TT - Temperature : IOO C Material : Quench Annealed Type Stainless Steel Solution : 0.1 N Sodium Sulfate Anodic Scon Rate : Minutes at Each Potential Cathodic Scan Rote : 10 mv/20 Seconds 0_:8ppm Current D e n sity,/x A /c m ^ Figure 85«Cathodic and anodic polarization curves of Type 30Zf stainless steel in oxygenated 0,1 N sodium sulfate solution at 100 C

200 .181 : Material : Quench Annealed Type Stainless Steel Temperature. '2 5 0 C Solution : O.i N Sodium Suifate e Ü T im e, M in u tes Figure 86. Current decay behavior of Type 304 stainless steel in 0,1 ÎI sodium sulfate solution at 250 C

201 182 Material: Q uench A nn ealed Type S ta in le ss Steel Temperature: 250 C Solution N Sodium S u lfate T im e, M in u tes F ig u re 87. C u rre n t d ecay b e h a v io r o f Type 304 s t a i n l e s s s t e e l in N sodium s u l f a t e s o lu tio n a t 250^0

202 s u r e 8 8. Potential/pH diagram at 200' C and unit activity of dissolved sulphur species. 183:

203 Figure 89, PotcnUal/pIl diagram at 300"C und unit activity of dissolved sulphur spec 184!

204 P U R E WATER 0 Sulfate Concentration, ppm Figure 90, Effect of sodium sulfate on the ph of water at 275 C

205 F igure 9 I,- Pokntîal/pH diagram for Fe-H^O-S system at 200 C.

206 F ig u re 9 2, Potcntial/pH diagram for Fc-H jo -S system at 300 C. ' 1 8 7

207 C o n c e n tr a tio n o f SO 4, ppm ' Temperature ' 2 50 C Material : Quench Annealed Type Stainless Steel D eaerafed - 1,000 Concentration of Sodium Sulfate, Normal Figureio5. Effect of sulfate on the corrosion potential of Type 304 stainless steel at 250 C

208 T I r-r-t-r t - M a te r ia l: Quench A nnealed Type 504 s t a i n l e s s s t e e l T em perature: 250 C S o lu tio n : D e a e ra te d 0,1 W Sodium S u lf a te P o t e n t i a l : 0 mvy 1.5 Exposure Time: 1000 M inutes. Ki.o - 4 ' g 0.5,I i_l_ ,000 10,000 S p u tte r in g Tim e, Seconds F ig u re 9 3, C o n c e n tra tio n p r o f i l e s o f oxygen apd s u l f u r i n o x id e film o f Type 304 s t a i n l e s s s t e e l.

209 Type S ta in le ss S te el 0.1 N Sodium S u lfa te C 0 mvn', 1,0 0 0 m inutes p u tte rin g Time; 1000 sec F ig u re S u rfa c e c o m p o sitio n o f Type 304 s t a i n l e s s s t e e l w ith AES

210 Table 8. E lectro ch em ical P aram eters in Oxygen R eduction K in e tic s c Tefel Slope < mv/decade of /Current Density k( 1-a) a z cal/uol Reaction D/rf S ± x 10-' x10-^ 7.23x x10-^ x 10-' x10-^ 1.27x10-'» 4.IxlQ-^ -4,000 n i l s x x10") 1.97x10-'* 4.2x10-^,60, lxlo x10-) 2.79x 10-'* 3.1x10-2

211 192f 1,200, HYPOTHETICAL POLARIZATION CURVE IN PURE WATER AT C 600 S te a d y / M a te r ia l: S t a t e / Quench A nnealed Type 504 S ta i n le s s S te e l 50 mv/20 min ppm " C u rre n t D e n s ity, ua/cm^ Figure 95, Cathodic and anodic polarization curves of Type 304 stainless steel in oxygenated water at 250 C

212 Concentration of Sulfate Ion, ppm Concentration of Sulfate Ion, normality F ig u re 95. E f f e c t o f Sodium S u lf a t e on th e ph o f W ater a t T e m p eratu res betw een 100 C and 288 C ^

213 Exchange Current Density, Vcrn^

214 195! F ig u r e 98. P o la r i z a t io n c u rv e s o f Type 304 s t a i n l e s s s t e e l i n o x y g en a ted 0.1 N sodium s u l f a t e a t 250 C ( a f t e r F u j i i e t. a l, )

215 U.) IB (/XA/cni^) 7 th TO-Blh SCAN* I qi o o CUnHt.Nr OtNSITY l/za/cm2 F ig u re 99'. Anodic p o l a r i z a t i o n c u rv e s o f Type 304 s t a i n l e s s s t e e l i n 0,01 W sodium s u l f a t e s o lu tio n a t 274 C ( a f t e r In d ig e t. a l. )

216 197 F e -3.1 C r N i F e C r-1oni JCAM RATE,^m1//sec, POTENTIAL (mvg) F ig u re 100, A nodic p o l a r i z a t i o n c u rv e s o f F e-n i-c r a l lo y s i n 0,01 N sodium s u l f a t e s o lu tio n a t 288 C ( a f t e r I n d ig e t. a l, )

217 F ig u re 'S u r f a c e m orphology o f Type 304 s t a i n l e s s s t e e l a f t e r th e c u r r e n t decay ex p e rim e n t i n 0,1 K sodium s u l f a t e a t 250 C m in. a t 0 mv^-, 2000X (by H.J. C hoi)

218 199 Fi m ire 102. S u rfa c e m orphology o f Type 30k s t a i n l e s s s t e e l a f t e r th e c u r r e n t decay e x n c rim en t in 0.01 H sodium s u l f a t e a t 25Ô C, 1000 m in, a t +100 mv^. 1200X (by I-I.J. Choi)

219 F ig u re 105. S u rfa c e m orphology o f Type 504 c t a i n l e s s s t e e l a f t e r 200 h o u rs exposu re i r p u re v ;a ter w ith 8 ppm oxygen, 1300X (by H.J. Choi)

220 0.8 - ;0.6 i 0.4 M a te r ia l: Quench A nnealed Type 304 s t a i n l e s s s t e e l T em perature: 250 C S o lu tio n : D e a e ra te d 0,1 N Sodium S u lf a t e P o t e n t i a l : 0 rav^ Exposure Time: 1000 M inutes ,000 10,000 S p u tte r in g Tim e, Seconds F ig u re IO4., S o n c e n tra tio n p r o f i l e o f Mi in o x id e film o f Type 304 s t a i n l e s s s t e e l

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224 205 I 38. J.F. S ykes, "The E f f e c ts o f D is so lv e d Oxygen, Tem p., H ydrazine, Hydrogen P eroxide; on th e C orrosion Potent i a l o f A llo y s C o n ta in in g I r o n, Chromium, N ic k e l and P u re N ic k e l in Aqueous S o lu tio n s a t E le v a te d Temp..'.',. M.S. T h e s is, The Ohio S ta te U n iv e r s ity, ( ) G eneral E l e c t r i c, " E v a lu a tio n o f N ear Term BWR P ip in g R em edies", P ro g re s s R e p o rt f o r E l e c t r i c Power R esearch I n s tit u te May, 1977, P M.E. In d ig and A.R, M c llre e, "H igh T em perature E le c tro c h e m ic a l S tu d ie s o f th e S tr e s s C o rro sio n o f Type 304 S t a i n l e s s S te e l", C o rro s io n /7 8, P resen ted in NACE Conference, in H ouston, Texas. March 6-1 0, M.E, In d ig and D.A, V erm ily ea, C o rro s io n, ( ), P , D.A, V erm ilyea and M.S. I n d ig, J. o f th e E le c tro ch e m ica l S o c ie ty, H 2, ( ), p R.E. Cowan and A.I. K aznoff, C o rro sion, 22_, p = A.E. A graw al an d R.W. S ta e h le, C o r r o s io n.3 3.( ). P R.S. G re e le y, W.T. S m ith, J r., R.W, S to u g h to n and M.H. L ie tz k e, J, o f P h y s ic a l C h em istry, 4 ^ (I9 6 0 ), p J.W. C obble, "C hem ical Thermo dynamic S tu d ie s o f Aqueous T race Components in L ig h t W ater R e a c to rs a t H igh T em p eratu re and P r e s s u r e ", P ro g re s s R eport f o r E l e c t r i c Power R esearc h I n s t i t u t e, C o n tra c t No. RP 311-2, San Diego S ta te U n iv e rsity, A p ril, W. H uebner, B. J o h an sso n and M. de P o u rb a ix, " S tu d ie s o f th e Tendency o f I n te r g r a n u la r C o rro s io n C rackin g o f A u s te n itic F e-c r-n i A llo y s i n High P u r ity W ater a t 300 C", AE-437, A k tie b o la g e t A tom energi, S tu d s v ik, N ykeoping, Sweden, R.L. Jon es, C orrosio n, 1, (1973), P 424.

225 206 ; 4 9, G en eral E l e c t r i c, " E v a lu a tio n o f N ear Term BWR P ip in g Rem edies" EPEI C o n tra c t RP701-1, November, 1976, p , T. F u j i i, T. K obayashi and G. I t o, "The I n f lu e n c e o f D is so lv e d Oxygen on th e E le c tro c h e m ic a l B eh a v io r o f M ild S te e l and S t a i n l e s s S te e l i n Aqueous S o lu tio n and T em peratures Above 100 C", High Tem perature H igh P r e s s u re E le c tro c h e m is tr y i n Aqueous S o lu tio n s, NACE,( ), p , A,J, D eb ethune, T,S, L ic h t and N, Swendeman, J, o f E le c tro c h e m ic a l S o c ie ty, 106. ( ), P 6 l6. 52, A.J, D ebethune, J,. o f. E le c tro c h e m ic a l S o c ie ty, IQ 2, (I9 6 0 ), p A.K. A graw al, D,G. Damin, R.D, M cc right and R.W, S ta e h le, C o rro s io n, 5J_, (1975) P Beckman I n s t r u c t i o n M anual, "M odel 735 D is so lv e d Oxygen A nalyzer". 55. ASTM D , '.'S tandard M ethods o f T e st f o r D is so lv e d Oxygen i n W ater", P a r t No. 51, ( ). 56. D.A, Jones,. C orrosion, ZG, (1970), p L.S, B u ch o ff, N.M. In g b e r an d J.H. B rady, A n a ly tic a l C h em istry, 22, ), P J. P. H oare "The E le c tro c h e m is try o f Oxygen" I n te r s c i e n c e P u b lis h e r s, ( ) A. D am janovic, " M e c h a n is tic A n a ly s is o f Oxygen E le c tro d e R e a c tio n s ", Modern A sp e cts o f E l e c t r o c h e m is try, No. 5, P 569, E d ite d by J O'M B o cliris B.E. Conway, Plenum P ress J. P, H oare "The Oxygen E le c tro d e on N oble M e ta ls ", A dvances i n E le c tro c h e m is tr y and E le c tro c h e m ic a l E n g in e e rin g, V ol. 6, p 201, E d ite d by P. D elahay, I n te r s c i e n c e P u b lis h e r, E.G. W ill, "The Oxygen E le c tro d e : A C r i t i c a l A ssesm ent", Power S ystem s L a b o ra to ry, R ep o rt No. 76CRD 276, Dec

226 207 : 6 2. E.L. V /hite, W.E. B e rry and W,K* Boyd, "The In f lu e n c e o f Combined E n v iro n m en tal E f f e c ts on S tr e s s C o rro sio n C rackin g o f W elded S t a i n l e s s S te e l p ip in g ", Q u a rte rly P ro g re s s R ep o rt f o r E l e c t r i c Power R esea rc h I n s t i t u t e P r o je c t Wo. R P 3J1-3, May 13, 1977, B a t t e l l e Columbus L a b o r a to r ie s, 63. I n s t r u c t i o n Manual f o r W ater A n a ly s is, C h em etrics In c. 64. G en eral E l e c t r i c, " E v a lu a tio n o f n e a r Term BWR P ip in g R em edies", P ro g re s s R ep o rt f o r EPRI, p 3-1, A pril-s eptem ber H.H, U h lig, " C o rro s io n and C o rro s io n C o n tr o l", p , John W iley & Sons I n c., S econd E d itio n, H. Gaunt and E.A.M. W etton, J. o f A p p lie d C hem istry,: London, j_6, ( ), p R.T. Lowson, B r itis h C orrosion Jo u rn a l, J_2, (1977), P L.F, A u d rie th and B.A. Ogg, "The C h em istry o f H y d ra z in e ", p 101, John W iley & S ons, I n c., (1951) 69. V.K. Gouda and S.M. Sayed, C orrosion S cien ce, 13, (1975), P C lin C hem icals, " S to ra g e and H an d lin g o f Aqueous H y d razin e S o lu ti o n s " H.H. U h lig, " C o rro s io n and C o rro s io n C o n tr o l! ", p , John W iley & Sons In c. Second E d itio n, ( ) G.W. W att and J.D. C h ris p, A n a ly tic a l C h em istry, 24, ( 1952) p W.D. F le tc h e r and L.F. P ic o n e, "S eco n d a ry Wa.ter T re atm e n t o f PWR Steam G e n e ra to r s ", P ro c e e d in g s 3 5 rd I n t e r n a t i o n a l W ater C o n fe re n c e, p H.H. U h lig, " C o rro s io n and C o rro s io n C o n t r o l ", p 258, John W iley & Sons I n c. Second E d i tio n, ( )- 73. Ib id. p 130.

227 M, S m ialow ski an.d Z, S z k la rsk a -S m ia lo w sk a, C o rro s io n, 1 8, ( ), p 1 t - 4 t T. F u j i i, " E le c tro c h e m ic a l S tu d y on th e C o rro s io n B e h a v io r o f M e ta ls and A llo y s i n Aqueous S o lu tio n s a t H igh T e m p eratu re an d P re s s u r e " T ra n s a c tio n s o f N a tio n a l R e s e a rc h I n s t i t u t e f o r M e ta ls, 1 8, ( ), P J. P. H oare, "The E le c tro c h e m is try o f O xygen", p , I n t e r s c i e n c e P u b lis h e r s, ( ). 79. M. P o u rb a ix, " A tla s o f E le c tro c h e m ic a l E q u i l i b r i a in Aqueous S o lu tio n s ", p 552, RACE, (1974). 80. S, S zklarska-s m ialow ska and G. M rowczynski, B r i t i s h C o rro s io n J o u r n a l, 1 0, ( ), P G.M. E lo r ia n o v ic h, L.A. S o k o lo v a and Y.M. K o lo ty rih v ^ E le c tro chim iea A cta, 12, (1967)» P G, Economy, R. S p e is e r, F.H. Beck and M.G, F ontana, J. o f E le c tro c h e m ic a l S o c ie ty, 108. ( ), p L. A brego, "A S tu d y o f th e E f f e c t o f S ilic o n on th e E le c tro c h e m ic a l B e h a v io r and P a s s iv e F ilm s o f I r o n - S i l i c o n A llo y s i n Aqueous E n v iro n m en ts", M.S. T h e s is, The Ohio S ta t e U n iv e r s ity, B. C ase, E le c tro c h im ic a A c ta, 1 8, ( ), P P. Cohen, "The C h em istry o f W ater and S o lu tio n s a t High T e m p eratu re f o r A p p lic a tio n s to C o rro sio n i n Power S y stem ", WAPD-5788, P re s e n te d a t th e S em inar on C h em istry and Aqueous C o rro s io n i n Steam G e n e r a to rs, E rm e n o n v ille, F ra n c e, M arch, M.S. S ty r ik o v ic h, 0,1. M artynova, Z.S. B elo v a, V.J-. M e n 'sh ik o v a an d B.P. N e ste ro v,d o k la d y A kadem ii Nauk SSSR, 1 8 2, ( ), P 1138

228 M.E. In d ig, P riv a te Comm unication. 88. W.L, M a rs h a ll and E.V. J o n e s, J, o f P h y s ic a l C h em istry, 2 0, ( ), P J.V /. C obble, "C hem ical Thermodynamic S tu d ie s o f Aqueous T ra c e Components i n L ig h t Water- R e a c to rs a t High T e m p eratu re and P r e s s u r e ", P ro g re s s R e p o rt f o r E l e c t r i c Power R esearc h I n s t i t u t e, C o n tra c t No. RP , San Diego S ta te U n iv e rsity, March 15, 1978, p4-5^

229 a ppen d ix es A ppendix A. Thermodynamic C a lc u la tio n s

230 Table 9«Thermodynamic Data [ - w î i t î (cal* m ole ^ ) (cal= raole~^ dog"^) (cai* m ole ^. deg ^) ir 0 0 Hg - 0 :) $ x1Q -^T x 105t"'^ Qx10-3t- Og :) -U.40xT 0;'T -^ H^O -56, gxlQ -^T + Fe G.Ô0x 1Q2T-^ Fe_0^ -242, x1O'^T l8,.6 0 x l0-3 T - Fe20^ , x T -2 Fe^+ -18, Ni x10-3 t WiO x10-3 t+ 50, x1 OPT-^ Ni^+ -10, x10-3T - Cr x105'T-^ x T - Cr , x107T -2 C rug , NOâ -8, NO" -26,

231 T able 10, Free E n erg ies of Form ation a t E lev ated T em peratures ( c a l m o le -1 ) T( C) H H O HgO Fe Fe^O^ Fe^O^ Fe^ Ni NiO N± Cr b CrgO^ G rog MO NO

232 Thermo dynam ic C a lc u la tio n s fo r th e C o n s tru c tio n o f P o te n tia l- p H D iagram s o f Iro n -N ick el-c h ro m iu m A llo y s in H igh T e m p eratu re A queous S o lu tio n s 213

233 1 ) Ü2 = 2H"^ + 2e 2H+ + 2e = Eg H + 2H+ = 2E+ + Eg El 00= PH ^150 ^ 0'084pH Epoo= PH "250=,= PH ^288= = 0-0. n ip H 2) ZE^O = 0^ + 4H'* + 4 4H+ + 4e = 2Eg 2HgO =02+ 2Hg ^100= PH E-,5o= PH 1^200= pH ^250~ , 104pH Eggg= O.nipH a g Ç = # ) El2+ + HgO = NIO + 2E+ 2pH 100 C : 2pH = 9.00 _ log(n i^+) 150 c : 2pH = 7.43 log(n i^+) 200 C : 2pH = log(n i^+) 250 C : 2pH = log(n i^+) 288 C : 2pH = logcni^"^) : AG^ 2.303RT, - logcni^"^)

234 215 4) N i + SgO = NiO + + 2e 2H+ + 2e = Ni + HgO = NiO + Hg - tj.qj.5t- ph ^100= 0, pH E^^q= 0, PH ^200= - 0'094pH ^2_^0~ 0,0 o l 0, 104pH ^288= llph 5) Ni = Ni^"^ + 2e 2H+ + 2e = lo g (N l2 + ) Ni + 2H'^ = Ni^ S^QQ= o g (N i2 + ) 2^50= og(N i^'^) o g (N i^ ^) 200" ^250= = og(N i^+ ) ^288= -0.T log(N i'^ '') 6 ) 5Fe + 4H2O = Fe^O^ + 8H'*' + 8e SH"^ + 8e = 4H2 g 3Fe + 4H2O = Fe^O^^ + 4^2 Z^QQ= pH pH ^200= pH ^250= - 0, , 104pH 2p83= -0, IpH AGÎ 2.305RT F ph

235 ?) 2F630^ + H^o = 3Fe2Û3 + 2E+ + 2e 2H+ + 2e = Hg ST= ZFej^Oj^ + H^O = 3^ H2 3ioo= 0, ,074pH S^3Q= ~ 0.084PH ^200= pH 2230= PH 2283= ^»^S ph 8) 3Fe2+ + 2iHpO ^ihgo : = F6 3 0 ^ + 8H+ + 2e 2h" + 2e = IÎ2 3Fe^+ + 4H2O = F830^ + 6H'^ + H2 ^ ^ 216 St = - 5 s 2 g 0 ^ i o g ( F e 2 - ^ ) - i S â, p H 2^00= O.nilogC F e^ -^ ) pH E^3o= log(F e^+) pH 2200= o g (F e2 + ) pH 2230= log(F e^ '^ ) PH 2288= og(Fe^'^) pH 9) Fe = Fe2+ + 2e 2: " ^ 2^ - Hp + 2 ^ p î l 0 g ( F e 2 - ^ ) Fe + 2H'*' = Fe^+ + H2 Eioo= og(Fe2+ ) 2 ^30= og(Fe2+ ) 2200= og(Fe^+ ) 2230= o g (F e -+ ) 2283= 0* o g (F e^+ ) ^ ^

236 10) 2Fe2+ + 3H2O = Fe H+ + 2e 2 F e H2O = F i+h'*' + Hg ^ ^ _ j x 2 ^ F 100= 0-5 % El 50= og(Fe^+ ) pH U o g (F e 2 + ) _ 0.252pH % oo= o g (F e^+ ) pH ^ 250= 0*357-0, 10410g (Fe^'*') - 0o312pH ^288= O.in io g C F e ^ '^ ) pH 11) 2Cr + 3H2O = Cr H'*' + 6e + 6e = 3H^ 3^= ^ ph 2Cr + 3HgO = Cr203 + Sioo= pH F-] 30= ,084pH ^200= «094pH E23q= ,104pH ^288= IpH ^ ^ 12) Cr H2O = 2Cr0^" + loh"^ + 6 e 6H+ + 6e = 3Hp Cr H2O = 2CrO^ + 3H2 + 4H+ ^ El00= E-l30= E2oo= _ 5X2^ 03ET og(C r0 ~ ) pH lo g ( C r o - ) pH cg (C r0^-) pH ^ 250= T o g ( C r o - ) ' pH ^288= T o g (C ro -) pH

237 0 C a l c u la tio n o f E q u ilib riu m P o t e n t i a l s as a F u n c tio n o f C o n c e n tr a tio n o f D is so lv e d S p e c ie s i n High T e m p eratu re Aqueous S o lu tio n s 218

238 219 : HgCaq) = 2H"''(aq) + 2e ( l ) H go d) = io ^ ( a q ) + 2S'^(aq) + 2 e ( 2 ) H^Og(aq) = OgCaq) + 2H"^(aq) + 2e ( 3 ) 25^0 (1 ) = HgO^Caq) + 2S"^(aq) + 2e ( 4 ) NgH^Caq) + 40H "(aq) = + 45^0 (1 ) + 4e (5 ) 2NH^(aq) + 20H -(aq ) = N ^E^(aq) + ZE^OCl) + 2 e ( 6 ) E O "(aq) + HgOCl) = NOg(aq) + 2H'*'(aq) + 2e (? ) Cr^O^Cs) + 5HgO(l) = 2CrO =(aq) + loh'^(aq) + 6 e ( 8) 1 = 4 - # ph Eg = E + I I in (a g ^ ) - 2 «^ 2 S T p H = E + g ph -5 - ^5 - # F ^ PH ^ "7 " "7 2F InC ajjo- / % o ;) - F ^8 " + H ^^(^CrO= ^^% F By H e n ry 's law K. = ^ 5. S E j: aqueous co n c. o f s p e c ie j P j : p a r t i a l p re s s u r e o f s p e c ie

239 T a b le 1 1.V alues o f H e n ry 's Lav/ C o n s ta n ts fo r Aqueous Hydrogen and Oxygen ( 4 6 ) t( c ) X 10^ ^Op X 10^ $ The u n i t s o f K a re m oles(kgh^o)""^/atm. E = - i In E = E ' In 4 = In 0^ T a b le 12. O x id a tio n P o t e n t i a l s f o r V ario u s E le c tro d e R e a c tio n s ( in V o lts ) t( c ) E ' 4 ' 4 ' , O

240 Table 13^ Neutral ph at High Temperature (35) T em perature ( C) e u t r a l S in c e = ( looom^)" ' 0 ^ ^ m^: m o lal c o n c e n tr a tio n o f s p e c ie i m olecular w eight o f sp ecie i p a r t s p e r m i llio n o f s p e c ie i E, = E ' + I n ( l O O O M j j ^ K j i ^ ) - In c 5 - p H 2^00= 0, log - O.G?4pH E^^q= lo g pH ^200= lo g pH % 0 = 0-0 % lo g pH Eggg= lo g - O.n ip H ^2 = # In(lOOOMQ^KQ^) + g : In cgp': - ph S^QQ= lo g pH E^^q= lo g Cg& PH E2QQ= lo g cgëm _ 0.094PH

241 ^ = " l o g o. l O ^ p H ^ = O. n i p H -. E3 = E ' - + II InCcgP-ZcPp^) - j=ioo= los(c m/cgeg ). 0.07ifpH ^ = O ' ^ log(og^' /C ^g^) P H Egÿo' Iog{0 5 /C?g ) PH 288= logccgfm/cgpg^) - o.lh ph \ = 4 - S l = ( ' O O O M g ^ g ^ ) + in C p^ - ph ^100= lo g cg^02 - ph ^ = l o g c g F g ^ _ p H ^ 250= T ' ^ l o g cgfg^ _ p H = l o g cgpg^ p H E 5 = E + m i n C l O O O M ^ ^ ^ ^ ) _ ^ i n cgpg^ + ^ ^ p O H. E i o o = l o g c g P g ^ = - ^ l o g C p ^ ^ 250 = " ^ l o g c p ^ ^ = - T ' % l o g c g g ^ E g = E ^ p in ( d O O O H i m P ^ + p I n Æ ) + e^qo= lo g ^ u g p ^ /( c P g ') 2 ) ' P O H = " ^ l 0 6 ( c g p / ( C g g ) ^ ) P 0 H E g ^ = l o g ( C g P g / ( C j ^ g ) ^ ) p O H

242 223 %88= O.m poe ^7 = ^ - ^ P H ^250= '77T log(cg 5/cgg5) _ 0.104pH Eg = Eg - ln ( M,^,= ). i, cggg= _ ^ ^ ^ ^ p E "250-

243 C a lc u la tio n s o f E q u ilib riu m Oxygen C o n c e n tra tio n o f F e, N i, and Cr ^jn.th t h e i r O xides i n H igh Temp, Aqueous S o lu tio n s 224

244 2 2 5 : c r + 02 = fcr^o ^ (1) 2-3 % (2 ) +02= 6Fe20^ (3) 2Ni + Op = 2NiO (4) From V an 't H off Isotherm AG^ = AG + ST In At e q u ilib riu m AG^ = -ST In r e a c t, ^ r e a c t. = -ST In ^ (assum ing pure phase) 2 = 4.575T lo g Pq^ T a b le 14, A G (c a l/m o le ) f o r th e r e a c tio n s \^ (oc) re x n i no, IO

245 226 Figure 15, Equilibrium P a rtia l Pressure of Oxygen r exils no. \ x 10""^ 8.48x10"^^ x 1 0 ^^ x 1 0 "^^ x 1 0 "^^ x 1 0 "^ ,27x10"^'^ If. 63x10 ^^ x 1 0 " x 1 0 ^'^ x 1 0 "^ ^ 1.39x10 ^^ x 1 0 "^^ x i o " ^ 1.19x10"^"^ x 1 0 "^ ^ x 1 0 "^ ^ x 1 0 " ^ 1.13x10"^ 1.14x10"^^ By H en ry 's law. Figure. I 6, E qu ilib riu m D isso lved Oxygen Conc.(mol/KgHgO) rexn> n o. \ x 10" '' 4.83x10 ^^ x10"'^^ x 1 0 "^ ^ x10""^^ x 1 0 "^ ^ x10 ^ ' 4.10x10"^^ x 1 0 "^^ x 1 0 "^^ x 1 0 "^ ^ x 1 0 "^^ x 1 0 " ^ x 1 0 ^^ 1. 32x 10 ^^ 2. 32x 10 ^^ 6,0 3 x 1 0 "^^ 1.13x10"^^ x 1 0 " ^ ' x 1 0 "^^

246 xio^ Z ^2 F ig u re 17^ E q u ilib riu m D is so lv e d Oxygen Conc, (ppb) \ ( C ) rex av 100 n o, \ ^4x10"^^ 1.35x10"^ 1.96x10"''^ 6.73x10"^^ x ,28x10"^^ x ^ x 1 0 "^^ 1. 86x 10 ^ x x 10"^ 4 1,1 7 x x 1 0 -^ x 10"^^ x 1 0 -^^ x 10'^ " 1. 31x 10"^^ x 1 0 -^ x 1 0 -^ x 10-^

247 APPENDIX B. M a te r ia ls 228

248 229 : Nominal Compositions Type 304 S t a i n l e s s S te e l (w e ig h t %) C Mn P S S i Cr Ni Fe <.0 8 < <.0 5 <.0 3 < b a l. In co n el 600 (v /eight %) C Mn Fe S S i Cu Ni Cr Inco lo y 800 (w eight %) C m Fe S S i Cu Ni Cr A1 T i N ic k e l, % (ppm) c 0 H N A1 Na Mg Ca T i <5.00 <30. 0 <30.0 <10.0 <10.0 <10.0 Fe Cu S i Cr Ni 1Tb Mo Ag Pb < 30.0 m ajor < <10.0 <30.0 Chromium, % (ppm) C 0 H N A1 Na Ca Fe Cu < < S i Cr Ni Ga Mo Ag Sn Pb m ajor- 10,.0 <10.0 < 10.0 <5.0 <10.0 <10.0 P la tin u m, Com m ercial P u r ity

249 2 ^. : Therm al H is to ry Type 304 s t a i n l e s s s t e e l, In c o n e l 600 and In c o lo y 800 : A nnealed a t 1030 C fo r 1 hour and w ater quenched N ick el: Annealed a t 700 C fo r 3 hours and a i r cooled Chromium: Vacuum m elted, c a s t and co ld machined P la tin u m : A s -re c e iv e d M ic ro s tru c tu re E tching C ondition Type 304 s t a i n l e s s s t e e l and In c o n e l 600 E tc h a n t: 10 g o x a lic a c id ml w a te r P ro c e d u re : E l e c t r o l y t i c e tc h in g a t 6 V f o r 60 s e c, I n c o lo y 800 E tc h a n t: 10 ml n i t r i c a c id + 20 ml h y d r o c h lo ric a c id + 40 ml g ly c e r o l P rocedure : Swab specim en fo r 1 hour N ic k e l E tc a n t: 1 p a r t n i t r i c a c id + 1 p a r t a c e t i c a c id P rocedure : Swab specim en fo r 10 seconds Chromium E tc h a n t: 30 ml h y d r o c h lo ric a c id + 10 ml n i t r i c a c id ml g ly c e r o l P rocedure : Sv/ab specim en fo r 2 hours

250 23:1 In c o n e l 600, 200X F ig u re io 6. M ic r o s tr u c tu r e s o f C r, N i, Type 304, Inco lo y 800 and Inco nel 600

251 232 Chromium, 200X N ic k e l, 200X F igure 106. C ontinued

252 23) Type 304 s t a i n l e s s s t e e l, 200X \ ï\ In c o lo y 800, 200X F igure IO6. C ontinued

253 APPENDIX G. F a c i l i t i e s 254

254 Figure 107. Control Panel and Instruments 235

255 236 F ig u re 108. M illip o r e V /ater P u r i f i c a t i o n C a r trid g e s and C o n d u c tiv ity M eter (Top R ig h t)

256 F ig u re 109. S to ra g e Tank (C a p a c ity : 200 l i t e r ) 237^

257 238" F ig u re 110. Argon Tank ( L e f t ). Oxygen Tank (C e n te r) and Gas P r o p o r tio n e r, M atheson Model No. 7352T (R ig h t)

258 239 D e a e ra tio n ta n k (bottom l e f t, 80 l i t e r ), m ixing ta n k (bottom r i g h t, 120 l i t e r ), ch e m ical s to r a g e tanlc ( to p, 4 l i t e r ) and chem ical m eterin g pump (m iddle)»

259 240 F igure 112. High P ressu re Pump (Yarway Model B)

260 24 T Â u-focîaves* a f t e r - c o o l e r ( r e a r r i g h t ), back p r e s s u r e r e g u l a t o r (to p l e f t ) and p re ssu re gauge ( to p r ig h t )