Processing and characterisation of Pr zircon pigment powder

Transcription

1 Proessing nd hrteristion of Pr ziron pigment powder J. K. Kr* 1, R. Stevens 2 nd C. R. Bowen 2 Prseodymium ziron pigment powders were suessfully prepred t different lintion tempertures with sodium fluoride NF s minerliser, using the solid stte synthesis method. The powders were hrterised using tehniques suh s XRD, SEM nd TEM. Qulittive investigtion of the phses using XRD showed the presene of lrge mounts of unreted zironi fter lintion t 900 nd 950uC, wheres from 1000 to 1200uC ziron ws found to e the mjor phse, together with smll mount of zironi. Quntittive investigtion of phses ws rried out using n externl stndrd method. The weight frtion of unreted zironi t 1000uC ws found to e SEM oservtion of powders exposed t vrious lintion tempertures indited the presene of tetrhedrl rystls, nd this ws enhned y the ddition of the NF minerliser. TEM oservtions showed lttie defets nd elsti strins in the smples t vrious lintion tempertures. Keywords: Pigment, Prseodymium, X-ry diffrtion, Ziron Introdution Nturl nd syntheti inorgni pigments produed nd mrketed s fine powders re n integrl prt of mny deortive nd protetive otings nd re used for mss olortion of mny mterils inluding glzes, ermi odies nd porelin enmels. 1 3 In suh pplitions, the pigments re dispersed in the ermi medi, forming heterogeneous mixture. Cermi pigments or stins sed on ziron re ommonly used in industril pplitions for glzes, owing to their high hemil durility, whih gives the speies superior resistne to dissolution during firing. 4,5 One exmple of syntheti inorgni pigment is zironium prseodymium yellow, whih elongs to the ziron pigment system. 6 8 The present pper reports the first quntittive investigtion of the mount of unreted zironi in the Pr ziron system in onjuntion with mirostruturl hrteristion of the pigment powders t different lintion tempertures. Quntifition of the weight frtion is importnt euse the mount of unreted zironi n influene the olour intensity of the pigment powder s well s the finl pplition within the glze. Experimentl proedure Smple preprtion Rw powders (ZrO 2, SiO 2,Pr 6 O 11 ) for the mnufture of Pr ziron yellow were mixed ording to the 1 Crorundum Universl Ltd, Industril Cermis Division, 47 Sipot Industril Complex, Hosur , Tmilndu, Indi 2 Mterils Reserh Centre, Deprtment of Engineering nd Applied Siene, University of Bth, Bth BA2 7AY, UK *Corresponding uthor, emil jiten_kr@hotmil.om required hemil omposition prior to ll milling for 1 h, using high density polyethylene plsti ottle ontining zironi grinding medi nd distilled wter s the liquid suspension. The min purpose of ll milling ws to intimtely mix the omponents to produe homogeneous powder. The milled powders were dried using n infrred lmp. A further milling stge ws performed using pestle nd mortr to rek up ny soft gglomertes. Powders were then pssed through 150 mm size sieve. The sieved powders were pled in new, pure lumin/ zironi ruiles nd sujeted to lintion t different tempertures nd for predetermined soking times for retion of the rw mterils to tke ple nd to llow inorportion of Pr 6 O 11 into the ziron host lttie. A dedited rolite muffle furne ws used for this purpose. A rmp rte of 300 K h -1 ws used during the heting yle, nd smples were furne ooled fter holding t the required temperture. The prepred smples of Pr ziron hd the hemil omposition Zr Pr SiO 4, with smple odes given in Tle 1. Preursors used were ZrO 2,SiO 2 nd Pr 6 O 11.NF (5 wt-% of totl mixture) ws used s the minerliser to id the formtion of the ziron lttie from the ZrO 2 nd SiO 2, effetively lowering the lintion tempertures. The rw mterils ZrO 2,SiO 2,Pr 6 O 11 nd NF (99% pure) were supplied y Treiher Auermet, Austri. During retion, the olouring oxide speies diffused into the lttie. Entrne of Pr 3z into the lttie ours simultneously with the ZrO 2 zsio 2 retion. This pigment is onsidered s solid solution of Pr 3z tion in ziron struture where Pr 3z reples Zr 4z tions. Smples of Pr ziron were het treted t 900, 950, 1000, 1100 nd 1200uC with 2 h soking time. Smples gve n intense yellow olour fter het tretment in the rnge uC. ß 2005 Institute of Mterils, Minerls nd Mining Pulished y Mney on ehlf of the Institute Reeived 5 August 2004; epted 16 Ferury 2005 DOI / X16699 Advnes in Applied Cermis 2005 VOL 104 NO 5 233

2 1 X-ry diffrtion pttern of pigment powder ZSPR, het treted t 900uC for 2 h Powders whih fter the vrious het tretments generted n intense or ttrtive olour were onsidered for further hrteristion using X-ry diffrtion (XRD) nd snning nd trnsmission eletron mirosopy (SEM, TEM). Fired smples were frited either in powder form or s prtilly sintered ermi mteril. The lined/sintered pigment powders were then ground for different periods using zironi grinding medi nd wter s the liquid suspension. The purpose of milling ws to redue the prtile size to predetermined level (verge prtile size 5 10 mm), s required for prtiulr ermi pplition, for exmple glss, tile or snitrywre. 2 X-ry diffrtion pttern of pigment powder ZSPR2, het treted t 1000uC for 2 h Results nd disussion X-ry diffrtion In order to determine the different phses present in the lined smples, X-ry diffrtion nlysis ws rried out, nd exmples of the resulting ptterns re given in Figs. 1 nd 2, whih show the diffrtion dt from smples lined t 900 nd 1000uC respetively. The XRD pttern of the smple shown in Fig. 1 indites tht the powder ws found to onsist of ziron nd lrge mount of unreted zironi nd sili. The sme pttern ws otined for the smple lined t 950uC. The XRD tre of the smple otined t 1000uC Chrteristion X-ry diffrtion XRD nlyses of the smples were performed on Philips PW1730/00 diffrtometer using monohromti Cu K rdition (l nm) nd with genertor voltge nd urrent of 40 kv nd 25 ma respetively. X-ry sns were mde etween 2h ngles of 10 nd 80u. A sn speed of 1. 0 s per step nd step size of 0. 02u were used. An externl stndrd method 9,10 ws used to lulte the weight frtion of unreted ZrO 2 in the mixture. Eletron mirosopy The struture of the Pr ziron smples ws exmined using Jeol JSM 6310 nlytil snning eletron mirosope fitted with 10/85 link mironlysis system, mnuftured y Oxford Instruments. Further exmintion of the powder mirostruture ws rried out using Jeol 2010 TEM to investigte the presene of defets, the nture of the grin oundries nd ny internl defet strutures. Genertion of olour is generlly ssoited with the presene of lttie defets, usully in the form of omplex vnies nd sustitutionl ion speies. 11 Tle 1 Smple Smples used for lintion: NF fluxing gent t 5 wt-% of totl mixture Clintion temp., uc ZSPR 900 ZSPR1 950 ZSPR ZSPR ZSPR ZSPR SEM imge of Pr ziron rystls fter lintion t uC with 2 h soking 234 Advnes in Applied Cermis 2005 VOL 104 NO 5

3 4 Drk (A) nd right (B) field imges of Pr ziron smple diffrtion pttern with indexing (C) fter lintion t 1000uC: tilt ngle z25.5u, mgnifition d (Fig. 2) shows tht the powder ws found to onsist of ziron, lthough tres of zironi were lso present. Similr diffrtion ptterns were otined from smples treted t 1100 nd 1200uC. Asene of peks for prseodymium oxide indites tht it hs diffused into the host rystl to form solid solution. Clultion of weight frtion of unreted zironi The weight frtion of unreted zironi w ws lulted nd is presented elow for Zr 0.95Pr 0.05SiO 4 lined t 1000uC. From Fig. 2, the high intensity pek of zironi n e seen to e Z(2111). With I s the intensity of the ZrO 2 pek in the heterogeneous mixture (266 from the rw sn) nd I p the intensity of the pure ZrO 2 pek (3147 from the rw sn), the weight frtion of unreted zironi w ws lulted s follows 9,10 I Ip ~ w (m =r ) (1) w (m =r {(m =r )zm =r where m nd m re the liner sorption oeffiients nd r nd r the densities respetively of ZrO 2 nd ZrSiO 4, m /r the mss sorption oeffiient of ZrO 2, nd m /r the mss sorption oeffiient of ZrSiO 4. The mss sorption oeffiients for ZrO 2 nd ZrSiO 4 were found to e 275 nd 176 respetively nd were lulted using the eqution 9,10 m~ n X (m ) V I (2) where n is the numer of moleules in the unit ell of the ompound, V the volume of the unit ell, nd X (m ) I? m A r N i where (m/r) i is the mss sorption oeffiient of the individul element using Cu K rdition, A the tomi numer of the element nd N Avogdro s numer ( ). Using eqution (1) nd sustituting the vlues of I, I p, m /r nd m /r, w ws lulted to e , s follows: ~ w 275 (w 98 : 41)z176 : 6 The weight frtion of unreted zironi present in the smple fter lintion t 1000uC ws thus found to e Similrly, the weight frtions of unreted zironi t 1100 nd 1200uC were found to e nerly , s the X-ry diffrtion intensities otined were lmost the sme, s desried ove. It is importnt to note tht the externl stndrd method is not pplile to smples ontining more thn two phses. At 900 nd 950uC, the smples onsist of multiple phses (more thn two phses) with little formtion of ziron. Thus the method presented ws not pplile to lultion of the weight frtion of unreted zironi t these tempertures. Snning eletron mirosopy SEM imges showing the morphology of smples generted t different tempertures re shown in Fig. 3. The imges from smples treted t different Advnes in Applied Cermis 2005 VOL 104 NO 5 235

4 1100uC there were numerous dislotions nd extensive elsti strin, wheres t 1200uC the rystl is lmost free of dislotions nd elsti strin. Indexing of the eletron diffrtion pttern from the smples treted t eh temperture shows the sme type of rystl struture (tetrgonl) ut with different orienttion. Lttie defets re generted s result of distortion in the lttie nd determine the intensity of the olour otinle in prtiulr system. The intense olour would e expeted in system when more lttie defets re present. 5 TEM imge of Pr ziron rystl diffrtion pttern with indexing fter lintion t 1100uC: tilt ngle z12.1u, mgnifition lintion tempertures indite tht the growth of the tetrhedrl shped rystls is enhned y the ddition of minerliser. At 1000uC two size rnges of rystl were evident, wheres t temperture of 1100uC the rystls were of uniform size. At temperture of 1200uC distint growth of rystls ws evident. Unreted zironi ws lso oserved in the mirogrphs, in good greement with the results otined y XRD, where the intensity peks due to ZrO 2 were lulted s eing equivlent to n unreted weight frtion. Trnsmission eletron mirosopy Investigtion of the nture of grin oundries nd lttie defets ws performed using TEM t 200 kv. TEM mirogrphs of smples fter lintion t different het tretment tempertures re shown in Figs The drk ontrst lines nd loops in the rystl re used y dislotions generted y the milling proess nd susequently modified y lintion tretment. From the TEM mirogrphs of rystls treted t different tempertures it ws seen tht t 1000 nd Colour mehnism The mehnism for olour formtion in the ziron host lttie n e explined on the sis of rystl field splitting The olour produed y n ion is due to the d or f eletrons moving ross the energy gp reted y the splitting of the rystl field. Rre erth oxides (Pr 6 O 11 ) hve seven f oritls whih hve the sme energy level in the ground stte. When Pr 6 O 11 is put in host lttie suh s ziron, Pr 3z reples one of the Zr tions of the host lttie. The tion it will e le to sustitute/reple depends on the size (ioni rdius) of eh of the ions nd the net energy of the finl system fter sustitution hs ourred. Sodium fluoride NF hs een used in the present work s minerliser to id the formtion of the host lttie struture t lower lintion temperture, nd lso to hieve the eletroneutrlity required in the ion sustitution proess. Consequently, owing to this intertion of f eletrons of the rre erth ion with the surrounding eletrons, the f oritls split into two groups, one hving higher energy thn the other (Fig. 7). There re two possile types of oritl energy splitting. One is tetrhedrl splitting where the rre erth ion is surrounded y tetrhedron of O 22 ions nd the seond is othedrl splitting where the rre erth ion is surrounded y n othedron of O 22 ions. The struture of the prseodymium doped ziron rystl is given in Fig. 8. The mgnitude of splitting for ions in n othedrl onfigurtion is greter thn in tetrhedrl euse six negtive ions re involved ompred to four in the tetrhedron, nd they re loser to the tion resulting in strong rystl field splitting. The trnsition of energy from the higher energy level to the lower energy level gives rise to the hrteristi olour if this hrteristi energy flls into the visile spetrum. In the present se, sine the energy flls in the yellow region of the spetrum, yellow olour is generted nd euse mny suh events tke ple the olour is intense. The degree of rystl field splitting will depend on the geometry of the surrounding ions nd how lose they re to the tive tion. This indites tht ny speifi rre erth tion n exhiit different olours in different host rystls, owing to the differene in trnsition energies. In Fig. 7, T 2g is the set of d oritls hving lower energy nd e g is the set of d oritls hving higher energy in the othedrl rystl field splitting; t 2 is the set of d oritls hving higher energy nd e is the set of d oritls hving lower energy in the tetrhedrl rystl field splitting. In n othedrl field the T 2g set hve lower energy nd the e g set higher energy with respet to the spheril group, wheres in tetrhedrl field the ondition is reversed. Crystl field splitting, tht is the seprtion of lower nd upper energy levels, is known s 236 Advnes in Applied Cermis 2005 VOL 104 NO 5

5 6 TEM imge of Pr ziron rystl diffrtion pttern with indexing fter lintion t 1200uC: tilt ngle z12.1u, mgnifition d 7 Exmple of rystl field splitting of hromophore ion in presene of host rystl D in othedrl splitting. In the se of tetrhedrl splitting it is hrterised s 4/9D. Conlusions 1. Inorportion of Pr 6 O 11 into the ziron host lttie y sustitutionl solid solution produed intense yellow olortion t lintion tempertures in the rnge uC. 2. From the XRD ptterns of smples treted t 900 nd 950uC, lrge mounts of unreted zironi were found to e present. At 1000, 1100 nd 1200uC, ziron ws found to e the mjor phse lthough tres of zironi were still deteted. 3. SEM mirogrphs reveled the presene of tetrhedrl rystls nd unreted zironi wheres TEM mirogrphs show the presene of dislotions nd elsti strins in the smples t different lintion tempertures. 4. Prseodymium doped ziron pigment is n exellent exmple of rystl field olour. The olour produed in this se is due to the f eletrons moving ross the energy gp reted y the rystl field splitting of the f oritls of the olouring ion Pr 3z. The mgnitude of the splitting depends on the intertions of f eletrons of the 8 Struture of prseodymium doped ziron rystls Pr 3z ion with the surrounding eletrons nd lso determines the intensity of the olour. In strong rystl field splitting, the intensity of the olour will e more intense, when ompred to wek rystl field splitting, owing to the involvement of greter numer of f eletrons in the trnsition proess. Aknowledgements The uthors re grteful to the Europen Commission for providing finnil ssistne nd to Treiher Auermet, Austri for supply of the rw mterils. Referenes 1. D. R. Eppler nd R. A. Eppler: Cerm. Eng. Si. Pro., 1997, 18, K. H. Hudson Winow nd J. Cowley: Cerm. Eng. Si. Pro., 1996, 17, K. Shw: Cermi olours nd pottery deortion ; 1962, London, Mlren nd Sons. 4. C. Deker: Cerm. Eng. Si. Pro., 1990, 11, R. W. Bthelor: Trns. J. Br. Cerm. So., 1974, 73, Advnes in Applied Cermis 2005 VOL 104 NO 5 237

6 6. R. A. Eppler: in Physis of eletroni mterils. Prt B, (ed. L. L. Henh nd D. B. Dove), ; 1972, New York, NY, Mrel Dekker. 7. J. Bretk, R. G. Bowmn nd T. Brown: J. Aust. Cerm So., 1981, 17, F. Bondioli, A. B. Corrdi, A. M. Ferrri nd T. Mnfredini: J. Am. Cerm. So., 2000, 83, Interntionl tles for X-ry rystllogrphy, 162; 1962, Birminghm, Kynoh Press. 10. B. D. Cullity: Elements of X-ry diffrtion, 2nd edn; 1978, London, Addison-Wesley. 11. R. Tilley: Colour nd optil properties of mterils ; 1999, Chihester, Wiley. 12. K. Nssu: The physis nd hemistry of olor (the fifteen uses of olor) ; 1983, New York, NY, Wiley. 13. F. Stern: Elementry theory of the optil properties of solids ; 1963, New York, NY, Ademi Press. 238 Advnes in Applied Cermis 2005 VOL 104 NO 5