Glass Transformation- -Range Range Glass Transformation Behavior- - - PowerPoint PPT Presentation

▶
glass transformation range range glass transformation
SMART_READER_LITE
LIVE PREVIEW

Glass Transformation- -Range Range Glass Transformation Behavior- - - PowerPoint PPT Presentation

Jan 22, 2023 160 likes •680 views

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

slide-1
SLIDE 1

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-1

Web Course Web Course Physical Properties of Glass Physical Properties of Glass

Glass Transformation Glass Transformation-

  • Range

Range Behavior Behavior-

  • Odds and Ends

Odds and Ends

Richard K. Brow Missouri University of Science & Technology Department of Materials Science & Engineering

slide-2
SLIDE 2

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-2

Outline

  • Memory Effect
  • Measuring Tg
  • Effect of composition and structure on Tg
slide-3
SLIDE 3

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-3

Properties depend on thermal history

Example: room temperature refractive index after quenching from different equilibrium temper-

  • atures. (Soak times >> relaxation times)
slide-4
SLIDE 4

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-4

The ‘room temperature’ properties

  • f glass depend on thermal history

….. but, just because properties are equivalent, doesn’t mean that thermal history and structure are the same…

  • Fig. 13-25
  • Borosilicate crown glass
  • 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 transition range

  • On re-heating to 530°C,

the glasses follow much different paths to the ‘equilibrium’

  • Memory Effect

A B Ritland (JAcerS, 1956) A single fictive temperature is insufficient to describe glass properties and structure

slide-5
SLIDE 5

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-5

The ‘memory effect’ is a consequence

  • f 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 temperature- “cross-

  • ver points” have

same properties but different thermal histories

⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = Φ

β

τ t t exp ) (

slide-6
SLIDE 6

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-6

The ‘memory effect’ depends on

fictive temperature history

Glass has a ‘memory’ of its most recent excursion through the transition range

  • Multiple relaxation processes

Initial equil.

585°C Crossover time

Final Equil.

500°C 545°C

slide-7
SLIDE 7

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-7

The Tool The Tool-

  • Narayanaswamy

Narayanaswamy model is one way to model is one way to account for the account for the ‘ ‘fictive temperature history fictive temperature history’ ’

⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ Δ − + Δ = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡− = Φ

∫ ∑

f i t i i i

RT H x RT H x dt g t * ) 1 ( * exp / ' exp ) ( τ τ τ

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

  • f 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

slide-8
SLIDE 8

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-8

Measuring Tg

1. Tg is defined by experimental conditions 2. Relaxation time ≈ experimental time 3. Dependent on thermal history (fictive temperature history)

slide-9
SLIDE 9

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-9

  • Changes in enthalpy- DTA, DSC
  • Changes in volume- dilatometry, TMA
  • Changes in mechanical modulus- DMA
  • Changes in transport properties
  • Etc.

Measuring Tg

slide-10
SLIDE 10

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-10

The glass transition temperature of………………. Spaghetti!

slide-11
SLIDE 11

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-11

T Tg

g can be determined from

can be determined from the temperature the temperature dependence of glass dependence of glass properties properties

Rahman, et al, Chem Phys Lett (2007)

slide-12
SLIDE 12

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-12

slide-13
SLIDE 13

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-13

What structural properties affect Tg?

  • 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

  • N3- > O2- > F-

Separation distance Potential energy

slide-14
SLIDE 14

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-14

T Tg

g decreases with the addition of modifiers to silica

decreases with the addition of modifiers to silica

Tg(°C) Mole% Na

2O

From Dingwell in Rev. Mineral. 32 (1995)

Tg/Tliq is a maximum (~0.7) at the eutectic

ΔTg~30°C

  • W. Vogel, Chemistry of Glass, 1985

G=U-1 ΔTliq~800°C

slide-15
SLIDE 15

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-15

Nitrogen increases Nitrogen increases T Tg

g

Hampshire et al, JACerS, 1984 Peterson et al., JACerS, 1995

slide-16
SLIDE 16

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-16

Adding nitrogen increases the average number of Adding nitrogen increases the average number of cross cross-

  • links between glass

links between glass-

  • forming tetrahedra

forming tetrahedra

slide-17
SLIDE 17

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-17

Composition and structure effects Composition and structure effects

  • n glass transition temperature
  • n glass transition temperature-
  • A few case studies

A few case studies

slide-18
SLIDE 18

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-18

Example 1: Phosphate Glasses

slide-19
SLIDE 19

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-19

Glass Network Structures Are Based on Glass Network Structures Are Based on Phosphate Tetrahedra Phosphate Tetrahedra

bridging

  • xygens

Q3 tetrahedron, [O]/[P]=2.5 Q2 tetrahedra, [O]/[P]=3.0 terminal

  • xygens

Q1 dimer, [O]/[P]=3.5 Isolated Q0, [O]/[P]=4.0 ultraphosphates metaphosphates p

  • l

y p h

  • s

p h a t e s

slide-20
SLIDE 20

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-20

mole fraction Na

2O

0.00 0.10 0.20 0.30 0.40 0.50

Relative Site Concentration

0.0 0.2 0.4 0.6 0.8 1.0

f(Q

2)=x/(1-x)

f(Q

3)=(1-2x)/(1-x)

ultra1.spw

Spectroscopic Studies Reveal Systematic Spectroscopic Studies Reveal Systematic Changes in Network Connectivity Changes in Network Connectivity

31P Chemical Shift (ppm)

  • 200
  • 150
  • 100
  • 50

50 100

0.40Na2O 0.30Na2O 0.20Na2O 0.10Na2O

96icg_6.spw

Q3 Q2

31P NMR Spectra

2Q3 + Na2O → 2Q2

slide-21
SLIDE 21

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-21

Alumina Additions Affect Alumina Additions Affect Metaphosphate Glass Properties Metaphosphate Glass Properties

Metwalli, Brow, JNCS, 289 2001

slide-22
SLIDE 22

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-22

96icg_8.spw

Glass Transition (°C)

300 400 500 600 700

mole fraction Al2O3

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Refractive Index

1.48 1.49 1.50 1.51 1.52 1.53

We Have Examined a Variety of We Have Examined a Variety of Sodium Aluminophosphate Glasses Sodium Aluminophosphate Glasses

οο ο ο οοοο ο ο οοο οο ο ο ο ο ο ο ο οο οο ο ο ο ο ο ο ο ο ο ο ο

P2O5 Na2O Al2O3

I II III IV

NaPO3 AlPO4 NaAlO2 Al(PO3)3 ‘basic’ compositions exhibit breaks in property trends.

slide-23
SLIDE 23

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-23

27 27Al MAS NMR Provides a Structural Explanation

Al MAS NMR Provides a Structural Explanation for the Composition/Property Behavior for the Composition/Property Behavior

27Al chemical shift (ppm)

xAl2O3 (1-x)NaPO3

27Al chemical shift (ppm)

Al(6) Al(5) Al(4) Al(6) Al(5) Al(4) 0.05Al2O3 0.10Al2O3 0.15Al2O3 0.20Al2O3 0.25Al2O3

increasing Al2O3: Al(6) → Al(4)

slide-24
SLIDE 24

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-24

10Al2O3•90RPO3 glasses

Al Al-

  • Coordination Depends on the Modifier

Coordination Depends on the Modifier

Ionic radius (A)

1.0 1.2 1.4 1.6

Average Al CN

5.0 5.2 5.4 5.6 5.8 6.0

27Al chemical shift (ppm)

  • 75
  • 50
  • 25

25 50 75

Cs Rb K Na Al(4) Al(5) Al(6)

Na K Rb Cs

Do large ions compete for NBO’s with Al-polyhedra?

slide-25
SLIDE 25

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-25

Chromatography Reveals that Alumina Chromatography Reveals that Alumina Reduces the Average Phosphate Chain Reduces the Average Phosphate Chain-

  • Length

Length

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000 P1 P2 P3 P3m P4 P5 P6 P7 >P7

Phosphate Anion Relative Concentration

10Al2O3 15Al2O3 20Al2O3 25Al2O3

mole fraction Al 2O3

0.05 0.10 0.15 0.20 0.25

Average P-chainlength

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Cs-series III glasses Na-series III glasses nav=(1-x)/3x

slide-26
SLIDE 26

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-26

Al Al-

  • Coordination and Glass Properties

Coordination and Glass Properties Depend on the Phosphate Chain Length Depend on the Phosphate Chain Length

[O]/[P] Ratio

3.0 3.5 4.0 4.5

Glass Transition (°C)

300 350 400 450 500 550

  • Avg. Al-Coordination

4.0 4.5 5.0 5.5 6.0

96icg_9.spw

'ortho-' 'pyro-' 'meta-' Al(6)

+

Na Al(6) Al(6) Al(6) O O- P O

  • O

O P O O Na

+

‘pyrophosphate’ O O P

  • O

O Na

+

Al(6) Al(4) Al(4) ‘orthophosphate’

Al coordination changes to maintain a neutral aluminophosphate network best sealing glasses

slide-27
SLIDE 27

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-27

O/P Ratio

100 200 300 400 500 600 700 2.5 2.7 2.9 3.1

Nd Gd La Li Na Tg (ºC)

La – Metwalli Li & Na - Hudgens

Tg minima

Ultraphosphate Glasses Exhibit T Ultraphosphate Glasses Exhibit Tg

g Minima

Minima

Metaphosphate (O/P=3) glasses generally have a greater Tg than P2O5

slide-28
SLIDE 28

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-28

Kreidl Kreidl Recognized the Recognized the Effects of Modifiers on Effects of Modifiers on the Properties of the Properties of Phosphate Glasses Phosphate Glasses

‘cross-linking’ modifiers?

slide-29
SLIDE 29

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-29

200 250 300 350 400 450 500 550 600 650 700 5 10 15 20 25 30 xRE2O3 · (1-x)P2O5 (mole%) Tg (C)

P2O5 LaP PrP NdP EuP TbP TmP LuP

The properties of rare The properties of rare-

  • earth phosphate

earth phosphate glasses depend on composition glasses depend on composition

slide-30
SLIDE 30

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-30

NPO with 3.7 - 4.1 P−P, R−P-distances estimated

0.0 0.1 0.2 0.3 0.4 400 800 1200

(a)

Q

max = 223 nm

  • 1

Yb Nd R = La R-P P-P O-O R-O P-O

Correlation function, T(r) /nm-2 Distance, r /nm

0.0 0.1 0.2 0.3 0.4 500 1000 1500

(b)

300 nm

  • 1

280 nm

  • 1

Q

max = 500 nm

  • 1

Yb Nd R = La O-O R-O P-O

Correlation function, T(r) /nm-2 Distance, r /nm

X-rays neutrons

X X-

  • ray and neutron diffraction results are

ray and neutron diffraction results are complementary complementary

Separation of the R Separation of the R− −O O and O and O− −O O-

  • contributions

contributions

slide-31
SLIDE 31

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-31

56 60 64 68 72 0.22 0.23 0.24 0.25

N

RO= 8

N

RO= 6

(b) R-O distance, rRO /nm R species given by z num bers

56 60 64 68 72 6 7 8 9

(a)

R-O coordination number, NRO

R species given by z num bers

15R2O3 25R2O3

‘ ‘Lanthanide contraction Lanthanide contraction’ ’ is evident in the is evident in the rare earth phosphate glasses rare earth phosphate glasses

CN

slide-32
SLIDE 32

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-32

mole fraction RE2O3

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

RE Coordination Number

5.0 6.0 7.0 8.0 9.0 10.0

La3+/XRD Nd3+/XAS Er3+/XAS Gd3+/XAS

RE CN depends on composition RE CN depends on composition

slide-33
SLIDE 33

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-33

Modifier coordination requirements are Modifier coordination requirements are satisfied by terminal oxygens satisfied by terminal oxygens

P O- O- RE O O P O O O P O O P O O P O O O O O P O O O P O O P O- O- RE O- O- RE O O- P O O- P O O- P O O O- O O P O O O P O O- P O O O

Low RE2O3: Isolated RE polyhedra

  • [TO]/RE3+ > CN(RE3+), (Hoppe, 1996)
  • depolymerized phosphate network

High RE2O3: Linked RE polyhedra

  • [TO]/RE3+ < CN(RE3+)
  • ionic bridges between Q2-tetrahedra
slide-34
SLIDE 34

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-34

Rules for RE Rules for RE3+

3+ incorporation into

incorporation into phosphate glass structures phosphate glass structures

NdP5O14

Isolated NdO8 species

  • P-O-Nd bonds to Q2

and Q3 tetrahedra 1. RE coordination environments include all terminal oxygens: Q3 P=O & Q2 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.

xRE2O3 (1-x)P2O5 glasses TO/RE3+ = (1+2x)/x

slide-35
SLIDE 35

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-35

mole fraction RE2O3

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

RE Coordination Number

5.0 6.0 7.0 8.0 9.0 10.0

La3+/XRD Nd3+/XAS Er3+/XAS Gd3+/XAS

RE CN decreases to avoid RE clusters RE CN decreases to avoid RE clusters

CN = TO/RE3+= (1+2x)/x Clustered REO6,7 units Isolated REO8,9 units

slide-36
SLIDE 36

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-36

Summary of the RE coordination Summary of the RE coordination environments in phosphate glasses environments in phosphate glasses

Q2 Q2

Isolated, large CN x < 7 mol% Large CN with common Q2 x > 7 mol% Decreasing CN 15 < x < 25 mol% Clustered, Low CN x > 25 mol%

slide-37
SLIDE 37

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-37

200 250 300 350 400 450 500 550 600 650 700 5 10 15 20 25 30 xRE2O3 · (1-x)P2O5 (mole%) Tg (C)

P2O5 LaP PrP NdP EuP TbP TmP LuP

Isolated RE polyhedra depolymerize network, Tg decreases RE-ions link neighboring Q2, Tg increases RE CN decreases, Tg is flat RE-O-RE bonds form, Tg increases

The structural model helps explain the effects of composition on The structural model helps explain the effects of composition on T Tg

g

slide-38
SLIDE 38

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-38

Morena, JNCS, 2000

PbO PbO-

  • free low

free low T Tg

g glasses

glasses have many possible have many possible applications applications

  • Low temperature processing
  • f optical glasses
  • Low temperature sealing

glasses

slide-39
SLIDE 39

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-39

Morena, JNCS, 2000

SnO/ZnO-pyrophosphate glasses have Tg’s under 300ºC

slide-40
SLIDE 40

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-40

We are evaluating glasses We are evaluating glasses in the in the Sn Sn-

  • borophosphate

borophosphate system system

  • Refractive indices >1.8
  • Tg<325ºC
  • Good aqueous durability
slide-41
SLIDE 41

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-41

200 400 600 800

  • 0.1

0.0 0.1

16% B 13% B 10% B 7% B 4% B 1% B 0% B

Delta T (

  • C/mg)

Temperature (

  • C)

T Tg

g increases with B

increases with B2

2O

O3

3-

  • additions

additions

Tg Tx Tmelt

200 220 240 260 280 300 320 340 360 5 10 15 20

Mol% B2O3 Tg (oC) Series I Series II

Is there a structural explanation for this trend in Tg?

slide-42
SLIDE 42

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-42

200 400 600 800 1000 1200 1400 10000 20000 30000 40000 50000 60000 70000 80000

740 924 986 1050

x= 0 x= 1 x= 4 x= 7 x= 10 x= 13 x= 16

(2y)SnO*(y)P2O5*(x)B2O3 (where x+3y = 100)

Relative Intensity (a.u.) Raman Shift (cm

  • 1)

Raman spectra indicate that the phosphate network is depolymerized by borate additions

P-O-P bend Q0

slide-43
SLIDE 43

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-43

  • 40
  • 35
  • 30
  • 25
  • 20
  • 15
  • 10
  • 5

0.00E+000 1.00E+008 2.00E+008 3.00E+008 4.00E+008 5.00E+008

Relative Intensity(a.u.) ppm 56SnO-28P2O5-16B2O3 60SnO-30P2O5-10B2O3 64SnO-32P2O5-4B2O3 66SnO-33P2O5-1B2O3

B(OP)4 B(OB)4 B(OB)3 Series I

  • 40
  • 35
  • 30
  • 25
  • 20
  • 15
  • 10
  • 5

0.00E+000 1.00E+008 2.00E+008 3.00E+008 4.00E+008 5.00E+008

Relative Intensity(a.u.) ppm 66.7SnO-17.3P2O5-16B2O3 66.7SnO-23.3P2O5-10B2O3 66.7SnO-29.3P2O5-4B2O3 66.7SnO-32.3P2O5-1B2O3

B(OP)4 B(OB)4 B(OB)3 Series II

11 11B NMR provides

B NMR provides an explanation for an explanation for the the T Tg

g trends

trends

slide-44
SLIDE 44

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-44

Example 2: Chalcogenide Glasses

slide-45
SLIDE 45

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-45

Tg Tg’ ’s s depend on average bond depend on average bond strength strength

Tichy and Ticha, JNCS, 1995 Heteropolar Pauling bond energies: As-Te 1.41eV As-As 1.38eV As-Se 1.8eV Sb-Sb 1.31eV Ge-Se2.12eV Ge-Ge 1.63eV….

slide-46
SLIDE 46

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-46

The Tg’s of covalent chalcogenide glasses depends on average CN

CN=Σxi·CNi CN(Ge)=4 CN(Se)=2 Increasing CN, increasing Tg

Feng et al, PRL, 1997

slide-47
SLIDE 47

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-47

Properties are considered with respect Properties are considered with respect structural rigidity structural rigidity

slide-48
SLIDE 48

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-48

Mauro and Varshneya, JACerS, 2007

Average coordination number defines Average coordination number defines network rigidity network rigidity

slide-49
SLIDE 49

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-49

Tichy and Ticha, JNCS, 1995

‘ ‘Something Something’ ’ happens happens near <r>=2.4 near <r>=2.4-

  • Other properties are

Other properties are sensitive to average sensitive to average CN CN

slide-50
SLIDE 50

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-50

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
slide-51
SLIDE 51

Adv Vitreous State/Glass Properties FS08 Richard K. Brow/Missouri S&T brow@mst.edu Web-based Course Glass Transformation 2-51

Best Wishes from the Glass Weenies at Missouri S&T! Best Wishes from the Glass Weenies at Missouri S&T!