Glass Transformation-Range Behavior- Odds and Ends

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1 Web Course Physical Properties of Glass Glass Transformation-Range Behavior- Odds and Ends Richard K. Brow Missouri University of Science & Technology Department of Materials Science & Engineering Glass Transformation 2-1

2 Outline Memory Effect Measuring T g Effect of composition and structure on T g Glass Transformation 2-2

3 Properties depend on thermal history Example: room temperature refractive index after quenching from different equilibrium temperatures. (Soak times >> relaxation times) Glass Transformation 2-3

4 The room temperature properties of glass depend on thermal history.. but, just because properties are equivalent, doesn t mean that thermal history and structure are the same Ritland (JAcerS, 1956) Borosilicate crown glass A Identical room temperature refractive indices from two thermal histories A: Soaked at 530 C for 24 hrs, then quenched B: Rate cooled at 16 C/hr through the B transition range On re-heating to 530 C, the glasses follow much different paths to the equilibrium Memory Effect Fig A single fictive temperature is insufficient to describe glass properties and structure Glass Transformation 2-4

5 The memory effect is a consequence of non-exponential relaxation Samples were initially stabilized at 585 C, quenched to room temp, then up quenched to the temperatures indicated Φ( t) t = exp τ β All properties measured at room temperature- crossover points have same properties but different thermal histories Glass Transformation 2-5

6 The memory effect depends on fictive temperature history Initial equil. 585 C Final Equil. 545 C 500 C Crossover time Glass has a memory of its most recent excursion through the transition range Multiple relaxation processes Glass Transformation 2-6

7 The Tool-Narayanaswamy model is one way to account for the fictive temperature history Φ ( t) = i g i exp xδh * τ i = τ 0 exp + RT t 0 dt' / τ i (1 x) ΔH RT f * Microscopic interpretation: Relaxation involves coupled responses of a series of processes with different reaction rates - bond 1 breaks, then bond 2.. Different regions within liquid relax at different rates because of structural differences (differences in configurational entropy from μ-region to μ- region) Glasses brought to the same point on a V-T diagram by different routes relax differently Glass Transformation 2-7

8 Measuring T g 1. T g is defined by experimental conditions 2. Relaxation time experimental time 3. Dependent on thermal history (fictive temperature history) Glass Transformation 2-8

9 Measuring Tg Changes in enthalpy- DTA, DSC Changes in volume- dilatometry, TMA Changes in mechanical modulus- DMA Changes in transport properties Etc. Glass Transformation 2-9

10 The glass transition temperature of. Spaghetti! Glass Transformation 2-10

11 T g can be determined from the temperature dependence of glass properties Rahman, et al, Chem Phys Lett (2007) Glass Transformation 2-11

12 Glass Transformation 2-12

13 What structural properties affect T g? Deep potential wells Strong network forming bonds More cross-linked networks Greater network coordination number More network bridges Greater modifier field strengths Greater anion coordination Potential energy Separation distance N 3- > O 2- > F - Glass Transformation 2-13

14 T g decreases with the addition of modifiers to silica From Dingwell in Rev. Mineral. 32 (1995) G=U -1 W. Vogel, Chemistry of Glass, 1985 ΔT g ~30 C T g ( C) Mole% Na 2 O ΔT liq ~800 C T g /T liq is a maximum (~0.7) at the eutectic Glass Transformation 2-14

15 Hampshire et al, JACerS, 1984 Nitrogen increases T g Peterson et al., JACerS, 1995 Glass Transformation 2-15

16 Adding nitrogen increases the average number of cross-links between glass-forming tetrahedra Glass Transformation 2-16

17 Composition and structure effects on glass transition temperature- A few case studies Glass Transformation 2-17

18 Example 1: Phosphate Glasses Glass Transformation 2-18

19 Glass Network Structures Are Based on Phosphate Tetrahedra ultraphosphates Q 3 tetrahedron, [O]/[P]=2.5 terminal oxygens bridging oxygens polyphosphates Q 2 tetrahedra, [O]/[P]=3.0 metaphosphates Q 1 dimer, [O]/[P]=3.5 Isolated Q 0, [O]/[P]=4.0 Glass Transformation 2-19

20 Spectroscopic Studies Reveal Systematic Changes in Network Connectivity 31 P NMR Spectra Q 2 Q Na 2 O 0.30Na 2 O 0.20Na 2 O 0.10Na 2 O P Chemical Shift (ppm) 96icg_6.spw Relative Site Concentration Q 3 + Na 2 O 2Q 2 f(q 3 )=(1-2x)/(1-x) f(q 2 )=x/(1-x) mole fraction Na 2 O ultra1.spw Glass Transformation 2-20

21 Alumina Additions Affect Metaphosphate Glass Properties Metwalli, Brow, JNCS, Glass Transformation 2-21

22 We Have Examined a Variety of Sodium Aluminophosphate Glasses P 2 O 5 Al(PO I 3 ) 3 οο ο ο ο οο ο ο NaPO 3 II οοοο AlPO ο 4 οοο ο οοο III ο IV Na 2 O NaAlO 2 Al 2 O 3 basic compositions exhibit breaks in property trends. Glass Transition ( C) Refractive Index mole fraction Al 2 O 3 96icg_8.spw Glass Transformation 2-22

23 27 Al MAS NMR Provides a Structural Explanation for the Composition/Property Behavior Al(6) Al(4) xal 2 O 3 (1-x)NaPO 3 Al(4) Al(5) increasing Al 2 O 3 : Al(6) Al(4) Al(5) Al(6) 0.15Al 2 O Al 2 O Al 2 O Al 2 O Al 2 O 3 27 Al chemical shift (ppm) 27 Al chemical shift (ppm) Glass Transformation 2-23

24 Al-Coordination Depends on the Modifier Al(4) Al(6) Al(5) 10Al 2 O 3 90RPO 3 glasses 6.0 Cs Rb Average Al CN 5.8 Na 5.6 K Rb Cs 75 K Na Al chemical shift (ppm) Do large ions compete for NBO s with Al-polyhedra? Ionic radius (A) Glass Transformation 2-24

25 Chromatography Reveals that Alumina Reduces the Average Phosphate Chain-Length Relative Concentration Al2O3 15Al2O3 20Al2O3 25Al2O3 Average P-chainlength Cs-series III glasses Na-series III glasses n av =(1-x)/3x mole fraction Al 2 O P1 P2 P3 P3m P4 P5 P6 P7 >P7 Phosphate Anion Glass Transformation 2-25

26 Avg. Al-Coordination Glass Transition ( C) Al-Coordination and Glass Properties Depend on the Phosphate Chain Length 'meta-' 'pyro-' best sealing glasses 'ortho-' Al coordination changes to maintain a neutral aluminophosphate network Al(6) O P Na + O- O O Al(6) Al(6) O P + O - Na O Al(6) pyrophosphate Al(4) O P Al(6) O O - Na + O Al(4) orthophosphate [O]/[P] Ratio 96icg_9.spw Glass Transformation 2-26

27 Ultraphosphate Glasses Exhibit T g Minima La Metwalli Li & Na - Hudgens Nd Gd La Li Na T g (ºC) Metaphosphate (O/P=3) glasses generally have a greater T g than P 2 O T g minima O/P Ratio Glass Transformation 2-27

28 Kreidl Recognized the Effects of Modifiers on the Properties of Phosphate Glasses cross-linking modifiers? Glass Transformation 2-28

29 The properties of rare-earth earth phosphate glasses depend on composition Tg (C) xre 2 O 3 (1-x)P 2 O 5 (mole%) P2O5 LaP PrP NdP EuP TbP TmP LuP Glass Transformation 2-29

30 Correlation function, T(r) /nm -2 X-ray and neutron diffraction results are complementary (a) Q max = 223 nm -1 R = La Nd Yb X-rays P-O R-O O-O P-P R-P Distance, r /nm Separation of the R O R and O O-contributionsO Correlation function, T(r) /nm (b) R = La Nd Yb neutrons P-O R-O O-O Q max = 500 nm nm nm Distance, r /nm N PO with P P, R P-distances estimated Glass Transformation 2-30

31 Lanthanide contraction is evident in the rare earth phosphate glasses (b) 9 (a) R-O distance, r RO /nm N RO = 6 N RO = 8 R-O coordination number, N RO R 2 O 3 CN 25R 2 O R species given by z numbers R species given by z numbers Glass Transformation 2-31

32 RE CN depends on composition RE Coordination Number La 3+ /XRD Nd 3+ /XAS Er 3+ /XAS Gd 3+ /XAS mole fraction RE 2 O 3 Glass Transformation 2-32

33 Modifier coordination requirements are satisfied by terminal oxygens Low RE 2 O 3 : Isolated RE polyhedra [TO]/RE 3+ > CN(RE 3+ ), (Hoppe, 1996) depolymerized phosphate network O O O O P O P O P O O - O O O P RE O - O P O P O O O O O P O O High RE 2 O 3 : Linked RE polyhedra [TO]/RE 3+ < CN(RE 3+ ) ionic bridges between Q 2 -tetrahedra O O O - O - P O P O P O O - O - O - O O P RE RE O O - O - O O P O P P O O - O O O - Glass Transformation 2-33

34 Rules for RE 3+ incorporation into phosphate glass structures 1. RE coordination environments include all terminal oxygens: Q 3 P=O & Q 2 P-O - 2. RE-O-RE clusters to be avoided 3. RE CN is consistent with Pauling s Rules: Minimum CN~6 Hoppe (1995): Metal coordination environment depends on the number of terminal oxygens per metal ion. xre 2 O 3 (1-x)P 2 O 5 glasses TO/RE 3+ = (1+2x)/x NdP 5 O 14 Isolated NdO 8 species P-O-Nd bonds to Q 2 and Q 3 tetrahedra Glass Transformation 2-34

35 RE CN decreases to avoid RE clusters RE Coordination Number Isolated REO 8,9 units CN = TO/RE 3+ = (1+2x)/x La 3+ /XRD Nd 3+ /XAS Er 3+ /XAS Gd 3+ /XAS Clustered REO 6,7 units mole fraction RE 2 O 3 Glass Transformation 2-35

36 Summary of the RE coordination environments in phosphate glasses Isolated, large CN x < 7 mol% Large CN with common Q 2 x > 7 mol% Q 2 Q 2 Clustered, Low CN x > 25 mol% Decreasing CN 15 < x < 25 mol% Glass Transformation 2-36

37 The structural model helps explain the effects of composition on T g Tg (C) Isolated RE polyhedra depolymerize network, T g decreases RE-ions link neighboring Q 2, T g increases RE CN decreases, T g is flat RE-O-RE bonds form, T g increases P2O5 LaP PrP NdP EuP TbP TmP LuP xre 2 O 3 (1-x)P 2 O 5 (mole%) Glass Transformation 2-37

38 PbO-free low T g glasses have many possible applications Low temperature processing of optical glasses Low temperature sealing glasses Morena, JNCS, 2000 Glass Transformation 2-38

39 SnO/ZnO-pyrophosphate glasses have T g s under 300ºC Morena, JNCS, 2000 Glass Transformation 2-39

40 We are evaluating glasses in the Sn-borophosphate system Refractive indices >1.8 T g <325ºC Good aqueous durability Glass Transformation 2-40

41 T g increases with B 2 O 3 -additions % B Delta T ( o C/mg) T g Tg ( o C) T280 x % B 10% B 7% B 4% B 1% B 0% B T melt Temperature 220 ( o C) Series I Series II Is there a structural explanation for this trend in T g? Mol% B 2 O 3 Glass Transformation 2-41

42 Raman spectra indicate that the phosphate network is depolymerized by borate additions (2y)SnO*(y)P2O5*(x)B 2 O 3 (where x+3y = 100) 1050 Relative Intensity (a.u.) P-O-P bend Q x= 0 x= 1 x= 4 x= 7 x= 10 0 x= 13 x= Raman Shift (cm -1 ) Glass Transformation 2-42

43 Relative Intensity(a.u.) 5.00E E E E E+008 Series I B(OP) E E+008 B(OB) 4 56SnO-28P2O5-16B2O3 60SnO-30P2O5-10B2O3 64SnO-32P2O5-4B2O3 66SnO-33P2O5-1B2O3 Series II B(OB) SnO-17.3P2O5-16B2O3 66.7SnO-23.3P2O5-10B2O3 66.7SnO-29.3P2O5-4B2O3 66.7SnO-32.3P2O5-1B2O3 0.00E B NMR provides an explanation for the T g trends Relative Intensity(a.u.) 3.00E+008 ppm 2.00E E E B(OP) 4 B(OB) 4 ppm B(OB) 3 Glass Transformation 2-43

44 Example 2: Chalcogenide Glasses Glass Transformation 2-44

45 Tg s depend on average bond strength Heteropolar Pauling bond energies: As-Te 1.41eV As-As 1.38eV As-Se 1.8eV Sb-Sb 1.31eV Ge-Se 2.12eV Ge-Ge 1.63eV. Tichy and Ticha, JNCS, 1995 Glass Transformation 2-45

46 The T g s of covalent chalcogenide glasses depends on average CN CN=Σx i CN i CN(Ge)=4 CN(Se)=2 Increasing CN, increasing T g Feng et al, PRL, 1997 Glass Transformation 2-46

47 Properties are considered with respect structural rigidity Glass Transformation 2-47

48 Average coordination number defines network rigidity Mauro and Varshneya, JACerS, 2007 Glass Transformation 2-48

49 Something happens near <r>=2.4- Other properties are sensitive to average CN Tichy and Ticha, JNCS, 1995 Glass Transformation 2-49

50 Summary of the Glass Transition Kinetic vs. thermodynamic transition? Depends on thermal history and experimental details Sensitive to structural details Important for many engineering applications Glass Transformation 2-50

51 Best Wishes from the Glass Weenies at Missouri S&T! Glass Transformation 2-51