Web Course Web Course Physical Properties of Glass Physical Properties of Glass Glass Transformation- -Range Range Glass Transformation Behavior- - Odds and Ends Odds and Ends Behavior Richard K. Brow Missouri University of Science & Technology Department of Materials Science & Engineering Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-1
Outline • Memory Effect • Measuring T g • Effect of composition and structure on T g Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-2
Properties depend on thermal history Example: room temperature refractive index after quenching from different equilibrium temper- atures. (Soak times >> relaxation times) Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-3
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 B 16°C/hr through the transition range •On re-heating to 530°C, the glasses follow much different paths to the ‘equilibrium’ • Memory Effect Fig. 13-25 A single fictive temperature is insufficient to describe glass properties and structure Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-4
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 All properties measured at room ⎡ β ⎤ ⎛ ⎞ temperature- “cross- t Φ = − ⎢ ⎜ ⎟ ⎥ ( t ) exp over points” have τ ⎝ ⎠ ⎢ ⎥ ⎣ ⎦ same properties but different thermal histories Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-5
The ‘memory effect’ depends on fictive temperature history Initial equil. Final 585°C Equil. 545°C 500°C Crossover time Glass has a ‘memory’ of its most recent excursion through the transition range • Multiple relaxation processes Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-6
The Tool- -Narayanaswamy Narayanaswamy model is one way to model is one way to The Tool account for the ‘ ‘fictive temperature history fictive temperature history’ ’ account for the Microscopic interpretation: ⎡− ⎤ t • Relaxation involves coupled ∑ ∫ Φ = τ ⎢ ⎥ ( t ) g exp dt ' / responses of a series of i i ⎣ ⎦ i processes with different 0 ⎡ ⎤ ‘reaction rates’- bond 1 breaks, Δ − Δ x H * ( 1 x ) H * τ = τ + ⎢ ⎥ then bond 2….. exp i 0 ⎢ ⎥ RT RT • Different regions within liquid ⎣ ⎦ f 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 Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-7
Measuring T g 1. T g is defined by experimental conditions 2. Relaxation time ≈ experimental time 3. Dependent on thermal history (fictive temperature history) Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-8
Measuring Tg • Changes in enthalpy- DTA, DSC • Changes in volume- dilatometry, TMA • Changes in mechanical modulus- DMA • Changes in transport properties • Etc. Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-9
The glass transition temperature of………………. Spaghetti! Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-10
T g can be determined from T g can be determined from the temperature the temperature dependence of glass dependence of glass properties properties Rahman, et al, Chem Phys Lett (2007) Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-11
Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-12
What structural properties affect T g ? • Deep potential wells – Strong network forming bonds – More cross-linked networks Potential energy • Greater network coordination number • More network bridges – Greater modifier field Separation strengths distance – Greater anion coordination • N 3- > O 2- > F - Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-13
T g decreases with the addition of modifiers to silica T g decreases with the addition of modifiers to silica W. Vogel, Chemistry of Glass , 1985 From Dingwell in Rev. Mineral . 32 (1995) G=U -1 Δ T g ~30°C T g (°C) Mole% Na 2 O Δ T liq ~800°C T g /T liq is a maximum (~0.7) at the eutectic Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-14
Nitrogen increases T T g Nitrogen increases Hampshire et al, JACerS, 1984 g Peterson et al., JACerS, 1995 Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-15
Adding nitrogen increases the average number of Adding nitrogen increases the average number of cross- -links between glass links between glass- -forming tetrahedra forming tetrahedra cross Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-16
Composition and structure effects Composition and structure effects on glass transition temperature- - on glass transition temperature A few case studies A few case studies Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-17
Example 1: Phosphate Glasses Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-18
Glass Network Structures Are Based on Glass Network Structures Are Based on Phosphate Tetrahedra Phosphate Tetrahedra metaphosphates terminal ultraphosphates oxygens bridging Q 3 tetrahedron, Q 2 tetrahedra, oxygens s e t a h [O]/[P]=2.5 [O]/[P]=3.0 p s o h p y l o p Q 1 dimer, Isolated Q 0 , [O]/[P]=3.5 [O]/[P]=4.0 Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-19
Spectroscopic Studies Reveal Systematic Spectroscopic Studies Reveal Systematic Changes in Network Connectivity Changes in Network Connectivity 31 P NMR Spectra 2Q 3 + Na 2 O → 2Q 2 ultra1.spw 1.0 Q 2 Relative Site Concentration Q 3 0.8 0.40Na 2 O 0.6 3 )=(1-2x)/(1-x) 0.30Na 2 O f(Q 0.4 0.20Na 2 O 0.2 2 )=x/(1-x) f(Q 0.10Na 2 O 0.0 0.00 0.10 0.20 0.30 0.40 0.50 100 50 0 -50 -100 -150 -200 mole fraction Na 2 O 31 P Chemical Shift (ppm) 96icg_6.spw Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-20
Alumina Additions Affect Alumina Additions Affect Metaphosphate Glass Properties Metaphosphate Glass Properties Metwalli, Brow, JNCS , 289 2001 Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-21
We Have Examined a Variety of We Have Examined a Variety of Sodium Aluminophosphate Glasses Sodium Aluminophosphate Glasses Glass Transition (°C) P 2 O 5 700 600 500 Al(PO 3 ) 3 I ο ο οοοο ο 400 ο II NaPO 3 οο ο οοο ο AlPO 4 οο ο 300 ο ο ο ο ο ο ο οο ο οο ο ο ο ο III ο ο ο 1.53 Refractive Index IV 1.52 1.51 1.50 NaAlO 2 Al 2 O 3 Na 2 O 1.49 ‘basic’ compositions exhibit 1.48 breaks in property trends. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 96icg_8.spw mole fraction Al 2 O 3 Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-22
27 Al MAS NMR Provides a Structural Explanation 27 Al MAS NMR Provides a Structural Explanation for the Composition/Property Behavior for the Composition/Property Behavior Al(6) Al(4) xAl 2 O 3 (1-x)NaPO 3 increasing Al 2 O 3 : Al(6) → Al(4) Al(4) Al(5) Al(5) Al(6) 0.15Al 2 O 3 0.25Al 2 O 3 0.10Al 2 O 3 0.05Al 2 O 3 0.20Al 2 O 3 27 Al chemical shift (ppm) 27 Al chemical shift (ppm) Adv Vitreous State/Glass Properties Richard K. Brow/Missouri S&T Web-based Course FS08 brow@mst.edu Glass Transformation 2-23
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