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Advanced Vitreous State: The Physical Properties of Glass Steve W. Martin MSE Iowa State University swmartin@iastate.edu 8/28/08 Lecture 1: Orientation Students so far Glass Class From Univ. Florida Gregory Grosso

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Advanced Vitreous State: The Physical Properties of Glass

Steve W. Martin MSE Iowa State University swmartin@iastate.edu 8/28/08 Lecture 1: Orientation

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Students so far…

Glass Class From Univ. Florida

Gregory Grosso GGrosso@Transitions.com

Matthew Strasberg mstrasberg@ufl.edu

Karthik Gopalakrishnan gaka1umt@ufl.edu

Robert Smith firefan@ufl.edu

Allyson Barrett abarrett@dental.ufl.edu

Prabhu Bellarmine pjbell@ufl.edu

Matthew Cimoch mcimoch@ufl.edu

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 2

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Students so far…

The students from ISU are:

Randilynn Christensen, rbchris@iastate.edu

Christian Bischoff, Christian.m.bischoff@gmail.com

Kristina Lord, krislord@iastate.edu

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Students so far…

From Alfred University

Joshua M. Bartlett JMB9@alfred.edu

Andrew B. Crawford ABC1@alfred.edu

Kathryn Goetschius KLG1@alfred.edu

Patrick K. Kreski: PKK1@alfred.edu

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Students so far…

From Clemson University

YANG JING JINGY@clemson.edu

CARLIE NATHAN A NCARLIE@clemson.edu

CHEN PENGYU PENGYUC@clemson.edu

MASSERA JONATHAN MASSERA@clemson.edu

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 5

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Students so far…

From Lehigh University

Belwalkar, Amit A. aab306@lehigh.edu

Saiyasombat, Chatree chs308@lehigh.edu

Stockdale, Andrew W. aws3@lehigh.edu

Stone, Adam R. ars208@lehigh.edu

Wang, Shaojie shw206@lehigh.edu

Zhao, Donghui doz206@lehigh.edu

Jain, R c100@lehigh.edu

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Students so far…

 From Penn State…

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Students so far…

 From Missouri S &T….

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Students so far…

 From Coe College…

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Students so far…

 From the University of Michigan…

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Students so far…

 From UC Davis….

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Students so far…

 From University of Arizona…

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Students so far…

 From….

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Advanced Vitreous State – Introduction

 The Details

 Meeting Times 1:00 – 2:15 EST  Delivery Web Site…

http://breeze.clemson.edu/vgc

 Course Blackboard (with content) web site

 https://bb.clemson.edu/webapps/portal/frameset.jsp

 Additional course info and alternative access to

important content through IMI site at… http://www.lehigh.edu/imi/PropertiesCourse.htm

swmartin@iastate.edu 14 Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1

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Advanced Vitreous State

The syllabus:

Syllabus

 

Tuesday and Thursday 1:00 – 2:15 PM EST

Beginning Aug. 28, 2008; Last Class: Dec. 9

Final exam: Dec. 11 Grades due: Dec. 15

Textbook: Varshneya, 2nd edition - order directly from Professor Arun Varshneya

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 15

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Advanced Vitreous State

 Syllabus:

Course Connection Practice Session

  • Aug. 26

1st Class- Admin and Introduction to Content

  • Aug. 28

Volume Properties of glass:

  • Sept. 2, 4, 9

Steve Feller, Coe College

Viscosity and Tg of Glass

  • Sept. 11,16, 18

Dick Brow, University of Missouri S & T

Thermal Properties of Glass

  • Sept. 23, 25, 30

John Kieffer, University of Michigan

Mechanical Properties of Glass

  • Oct. 2, 9, 14

Jack Mecholsky, University of Florida

MS&T No Class

  • Oct. 6, 7, 8

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 16

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Advanced Vitreous State

Strengthening of Glass

  • Oct. 16, 21

Arun Varshneya, Alfred University

Passive Optical Properties of Glass

  • Oct. 23, 28, 30

Pierre Lucas, University of Arizona

Active Optical Properties of Glass

  • Nov. 4, 6, 11

Denise Krol, University of CA at Davis

Charge Polarization properties of Glass

  • Nov. 13, 18, 20

Himanshu Jain, Lehigh University

Thanksgiving week no classes

  • Nov. 24-28

Charge Conduction Properties of Glass:

  • Dec. 2, 4, 9

Steve Martin, Iowa State Properties

Course Summary and Wrap-up

  • Dec. 11

Grades in - last day

  • Dec. 15

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 17

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Adavnced Vitreous State

 Questions…?

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 18

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Advance Vitreous State

 HW

 Each section  By the instructor  Graded by the instructor  Final grades assigned by “local” instructor

swmartin@iastate.edu Advanced Vitreous State - The Properties of Glass: Overview and Introduction Lecture 1 19

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 20

Fundamentals of the Glass Transition

 The Glass Transition is a Kinetic Transition

 Continuous changes in structure and properties  Structure and properties are continuous with temperature  Structures and properties can be changed continuously by

changing the kinetics of the cooled or reheated liquid

 Melting and Crystallization are Thermodynamic

Transitions

 Discontinuous changes in structure and properties and Tm  Structures are thermodynamically controlled and described by the

Phase Diagram

 Tmelting and Tliquidus have fixed and specific values, 1710 oC for SiO2,

for example

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 21

Glass Transition as a Kinetic Transition

 Let’s construct a cooling curve for a liquid that will

ultimately form a crystal

 Consider SiO2, Tm = 1,710 oC  Suppose we measure the volume of the liquid as it cools  Sketch the temperature dependence of the volume from

2,000oC to 25 oC if one mole of SiO2 (60 grams) is cooled at 10 oC/min.

 1st assume that thermodynamics controls the system, the liquid

crystallizes where it should

 2nd assume kinetics controls the system, the liquid changes

properties and structures only if it is given ‘sufficient” time to change

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 22

Crystallization is Controlled by Thermodynamics

Volume is high as a hot liquid

Volume shrinks as liquid is cooled

At the melting point, Tm, the liquid crystallizes to the thermodynamically stable crystalline phase

More compact (generally) crystalline phase has a smaller volume

The Crystal then shrinks as it is further cooled to room temperature

Slope of the cooling curve for liquid and solid is the thermal expansion coefficient, a

Temperature Volume liquid crystal Tm aliquid acrystal aliquid >>acrystal Vcrystallization

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 23

Glass Formation is Controlled by Kinetics

Glass forming liquids are those that are able to “by-pass” the melting point, Tm

Liquid may have a high viscosity that makes it difficult for atoms of the liquid to diffuse (rearrange) into the crystalline structure

Liquid maybe cooled so fast that it does not have enough time to crystallize

Two time scales are present

 “Internal” time scale controlled

by the viscosity (bonding) of the liquid

 “External” timescale controlled

by the cooling rate of the liquid

Temperature Molar Volume liquid glass Lecture 1 ended here

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 24

The Glass Transition is a Kinetic Transition

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 25

Time and Temperature Dependence of Properties

Property P or H time  << t  >> t   ~ t T t Sample T Enthalpy (heat content) of sample

  • r

Property (volume) of sample liquid glass

At high temperatures, Liquid can reach equilibrium after T step, relaxation time  is short compared to time allowed At low temperatures, Liquid cannot reach equilibrium after T step,  is long compared to time allowed

Average cooling rate, T = T/ t

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 26

Temperature dependence of the internal time scale

While the external time scale, t most often does not change,

The internal timescale can be strongly temperature dependent,

Rearrangement of the liquid requires breaking of bonds between atoms (ions)

This requires thermal energy

The relative magnitude of the energy barrier to motion, Eact< and the available thermal energy, kT determines the probability of “getting over” the energy barrier

Arrhenius temperature dependence of the “relaxation time”

t T T   

/

Eact

         kT E T

act

  • exp

) (  

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 27

Temperature dependence of the internal relaxation time

For Eact > 0

0  1

It is a thermal “probability” of motion

High T, kT ~ Eact, high probability of motion

Low T, kT << Eact low probability of motion

       kT E T

act

  • exp

) (          kT E T

act

exp / ) (  

Temperature dependence of tau

  • 0.2

0.2 0.4 0.6 0.8 1 500 1000 1500 2000 2500 T(K) tau(T)/tau0

1000 10000 50000 100000 200000

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 28

Temperature dependence of the internal relaxation time

For Eact > 0

0  1

It is a thermal “probability” of motion

High T, kT ~ Eact, high probability of motion

Low T, kT << Eact low probability of motion

Arrhenius Temperature dependence of tau 1.0E-20 1.0E-18 1.0E-16 1.0E-14 1.0E-12 1.0E-10 1.0E-08 1.0E-06 1.0E-04 1.0E-02 1.0E+00 0.001 0.002 0.003 0.004

1/T(K) log10(tau/tau0)

1000 10000 50000 100000 200000

kT E T

act

            ) ( log10

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 29

Glass Transition is a Kinetic Transition

Glass formation is a kinetic transition, therefore, it depends upon the kinetics of the process

 The internal timescale, , for the process is controlled by the

atomic or ionic bonding between atoms or ions

Strong and numerous bonding increases the viscosity

Weak and limited bonding decreases the viscosity

Viscosity  relaxation time,  = G

 The external timescale, t, is controlled by the experiment or

process, i.e., how fast is the liquid cooled

Is it purposefully quenched very fast? t is short

Is it just allowed to cool naturally under prevailing conditions?

Or is it “insulated” and allowed to cool very slowly, t is long

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 30

The Glass transition from Arrhenius T dependence of tau

Volume vs. Temperature

18 20 22 24 26 28 30 400 500 600 700 800 900 1000

Temperature (K) V(ml/mol) tau = 1 x 10-13secs exp(-50,000cal/mol/RT) VVo(1+a

  • 10oC/min
  • 1oC/min
  • 1000oC/min

+10oC/min

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 31

Examples of Poor and Good Glassformers

 Why is water, H2O, found to be a very “weak” glass

former

 Requires cooling the liquid faster than 1,000,000 oC/min  300 to 150K in 9 milliseconds!!  What is the atomic structure?  Talk to your neighbor and sketch the structure of 5 water

molecules

 Why is silica, SiO2, found to be a very “strong” glass

former

 Can be cooled at 10-10C/min and still by-pass Tm without

crystallizing

 2,000 oC to 1,000 oC in 20 million years!!  What is its atomic structure? Talk to your neighbor and sketch the

structure of 5 SiO2 molecular units

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 32

Structure of Water compared to Silica

H2O No bonding between molecules and molecules can easily flow by each other SiO4/2 Each Si is tetrahedrally bonded to O, Si and O atoms cannot move unless other neighboring atoms also move

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 33

Cooling Rate Affects Properties of Glass

 Cooling rate, the external time scale, affects the

properties of glass

 Faster cooling rates decrease the time the liquid has

to “relax”, the time to readjust to the temperature change, to the properties at the new (lower) temperature

 Slower cooling rates increase the time the liquid has to

relax to the properties at the new temperature

 Fast cooling freezes the structure of the liquid (glass)

in at a higher temperature, therefore it has properties corresponding to these high temperatures

 Slower cooling enables the structure to freeze in at a

lower temperature and therefore the glass has properties corresponding to to these lower temperatures

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 34

The Cooling Rate Affects the Properties of Glass

Faster cooling freezes in the glass at a higher temperature

The temperature is lowered so fast that the liquid does not have time to relax to the properties at the next lower temperature, glass is formed at a high temperature

Slower cooling freezes in the glass at a lower temperature

The temperature is lowered slowly enough that the liquids can relax to properties at lower and lower temperatures, glass is eventually formed at a lower temperature

Temperature Molar Volume liquid slow medium Fast cooling supercooled liquid glassy state

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 35

Glass Properties on Heating

 If a glass is reheated, how do the properties

change?

 Sketch a temperature plot for a glass that has

been cooled at a average rate of 10oC/min and then is reheated at 10oC/min.

 How does the volume change upon reheating?  Does it follow the same curve as the cooling

curve?

 Does it follow a different path?

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 36

Glass Properties on Heating

Liquid is “arrested” in the glassy solid state on cooling

On reheating, the curve does not follow the same curve, as it would for a crystal

Tg is higher on heating because of hysteresis

The heating curve by-passes the cooling curve because the glass is frozen, it is “stuck” and does not want to change

Soon above the Tg, however, the glass has the thermal energy necessary to become a liquid and the two curves rejoin

Temperature Molar Volume liquid glass supercooled liquid crystal cooling reheating

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MSE 423 Section 1: Fundamentals of the Glassy State, Kinetics 37

Glass Properties on Reheating

Temperature Molar Volume liquid glass supercooled liquid crystal fast slow

Glasses arrested at progressively lower temperatures, the slower the cooling

Tg decreases with decreasing cooling rate

Slower cooling produces a lower Tg

Faster cooling produces a higher Tg

Tg is higher on heating because of hysteresis

The heating curve by-passes the cooling curve because the glass is frozen, it is kinetically “stuck”

Soon above the Tg, however, the glass has the necessary thermal energyto become a liquid and the two curves rejoin