Material Science II Ceramic Materials Chapter 5: Glass 5: Glass. Ceramics ... Chap 5 slide 2...

Ceramics: Glass, Chap 5

Material Science II

Ceramic Materials

F. Filser & L.J. GaucklerETH-Zürich, Departement Materials

[email protected]

SS 2007

Chapter 5: Glass


Material Science II

Persons in Charge of this Lecture• I. Akartuna,

HCI G 538, phone 36842, [email protected]. KraussHCI G 538, phone 3 68 34, [email protected]

• Dr. F. Filser, HCI G 529, phone 26435, [email protected]

• Prof. Dr. L.J. GaucklerHCI G 535, phone 25646, [email protected]

• Dipl.-Ing. J. KüblerEMPA Dübendorf, phone 044 823 4223, [email protected]


Material Science II

Materials Science I: Ceramics

Introduction on ceramic materials, technology, applications

Crystal structures of ceramic materials

Potential well of bonding and physical properties &Examples of Structural ceramic materials

Examples of structural ceramic materials


Material Science II

Overview & schedule

Mar 19, 07 term start

Mar 20, 07 Glass and Glass-Ceramics (FF)

Mar 27, 07 Toughness (JK)

Apr 03, 07 Strength & Weibull statistics (JK)

Apr 10, 07 Sub-critical crack growth, SPT-Diagrams (JK)

Apr 17, 07 Proof-testing, creep, thermal properties (JK)

Apr 24, 07 polymer part (Prof. D. Schlüter)

Jun 22, 07 term finish


Material Science II

Learning Targets

• Definition of glass as a “frozen” liquid

• Viscosity – temperature – behavior

• Structure of Glass, Network

• Network formers, network modifiers, and Zwischenoxide

• Optical properties (refraction, dispersion, transmission)

• Chemical resistance and corrosion

• Fabrication of glass

• Glass ceramics, nucleation rate und crystal growth rate


Material Science II

V-T-Diagram for Crystal and for Glass Formation

ΔV solidification

Volmelt - Volcryst

Melt

Crystal

Glass

supercooledliquidV

olum

e

TemperatureTfTgTg

slowfast

• Glasses are frozen liquids.• They don’t posses a (distinct) melting temperature but a glass transition temperature.• The glass transition temperature and the density of a glass depend on the cooling rate.• We don’t observe a energy of formation during the solidification of a glass melt.• In glass state the disorder of the melt is preserved.

frozenliquid


Material Science II

History:W. H. Bragg and W. Lawrence Bragg

W.H. Bragg (father) and William Lawrence Bragg (son) developed a simple relation for scattering angles, now call Bragg’s law.

θλ

sin2 ⋅⋅

=nd


Material Science II

Another View of Bragg´s Law

nλ = 2d sinθ


Material Science II

Laue - Powder X-ray Diffraction

Tube

Powder

Film


Material Science II

Bragg diffraction of glassy and crystalline material (PbF2)


Material Science II

Laue-Diagram for a Single Crystal

(Points)

single crystal

aperture

film


Material Science II

Zachariasen’s Network-Hypothesis

2-dimensionel visualization of a - regular SiO4 - network (SiO2 - quartz, left) and of a - irregular network (glass, right)


Material Science II

[SiO4] - Network

[SiO4] - network with network modifiers Na and Ca


Material Science II

Glass

GlassShort range order = Tetrahedron

[SiO4]4-

TetrahedronSi4+

O2-

O2-O2-O2-

z.B. Na+,K+

O2- Si4+

Si4+

O2-


Material Science II

Network Former

UV transparency ↑IR transparency ↓chem. resistance ↓

P2O5

α↑ → thermocycling↓Tg↓ → η↓acid resistancemech. strength ↓

B2O3

α↓ → thermocycling↑Tg↑ → η↑mech. strength ↑

SiO2

Network former and their influence on the glass‘ properties.


Material Science II

Network Modifier

a. Glasses are termed “long” or “short” glasses according to their Viscosity-Temperature-Function.

chem. resistance ↑CaO

Glass becomes „longer“aK2O

η↓Na2O

η↓↓Li2O


Material Science II

Zwischenoxide

absorption of thermal neutrons (30-60 weight-%)CdOhardness ↑ZnO

chem. resistance ↑tarnish for enamels

ZrO2

n ↑resistance against acids ↑

TiO2

Tg↓n ↑electrical resistance ↑Absorption of x-rays (40-80 weight-%)

PbO

Glass becomes “longer“mech. strength ↑chem. resistance ↑

Al2O3

Glass becomes “longer“MgO


Material Science II

Typical Glass Compositions I

SiO2 72, B2O3 10Al2O3 3, CaO 1, MgO 1, Na2O 5 (weight-%)

chem. laboratory glass (aluminium-borosilicate glass)

SiO2 72,Al2O3 1.5, MgO 3.5CaO 8.5, Na2O 14.5 (weight-%)

Commercial window glass

96 weight-% SiO2, 3 weight-% B2O3, rest alkali, impurities in the ppm-rangeα=0.8·10-6 K-1

Vycor Glass

>99.9 weight-% SiO2

impurities in the ppm-rangeα=0.5·10-6 K-1

pure vitreous silica (quartz glass)


Material Science II

Typical Glass Compositions II

P2O5 72,Al2O3 18, ZnO 10 (weight%)

„hydrofluoric acid“ resisting glass

B2O3 83,BeO 2, Li2O 15 (weight%)

X-ray transparent glass

SiO2 29,PbO 62,BaO 9 (weight%)

glass for X-ray protection

SiO2 28,PbO 70,Na2O 1, K2O 1 (weight-%)

optical glass(heavy flint glass)


Material Science II

0

log BAT T

η = +−

Vogel-Fulcher-TammanEquation

• Glass softens steadily but doesn‘t melt (at a distinct temperature)!• The viscosity of glass is a steady curve which spans 16 to 18 orders of magnitude.• „Melt“ exists for temperature higher than Tg (= infexion point of its viscosity curve), „solid“

exists for a temp. lower than Tg. • VFT-equation describes the viscosity for temperatures higher than Tg.

Viscosity of Glass Melts

η = 1013 dPa·s


Material Science II

“long” Glass – “short” Glass

η-T-function of Dow-Corning‘s glasses („long" glass, „short" glass)

ηin

log

dPas

T in °C

long glass

short glass


Material Science II

Elongation of Glass I

Dilatometry for the determination of Tg and α of a glass.

1/th ollT

α Δ=

Δi


Material Science II

Cooling RateInfluence of the cooling rate on the formation of glass.

• Tg and density of a glass depend on the cooling rate. • A low cooling rate (i.e. slow cooling) leads to higher density than a high cooling rate.

volu

me

glas

s

temperature

melt

cooling

fast

normal

slow

Tgs Tgn Tgf


Material Science II

Elongation of Glass II

Contraction and elongation curves of a glass. 0: equilibrium curve; 1: normal cooling; 2: slow cooling; 3: fast cooling; 3’: normal heating


Material Science II

Density as function of the alkali amount

Density of binary alkalisilicate glasses


Material Science IIDensity as a function

of the network former and its amount

Density variation of a binary alkalisilicate glass in function of the replacement of SiO2 by other oxides in the same weight amount.


Material Science II

Reduction of the strength caused by flows

Strength of glass and its reasons

theoretic strengthstrength ofglass fibers

strength of brand new acid polished glass

stre

ngth

Flaws in glass structure

Micro flaws in the surface

Macro flaws in the surface

strength of normal glass ware

strength of damagedglass ware


Material Science IIPre-stressing

Stress profiles for the a) thermal and the b) chemical method of pre-stressing.

a) b)

tension compression

surface

surface


Material Science II

Chemical Resistance of Glasses

• hydrofluoric acid HF attack (corrosion)

• diluted aqueous acids attack

• base attack

• combined water and acid / base attack


Material Science II

Chemical Resistance of Glass against Hydrofluoric Acid HF

SiO2 + 6HF → H2SiF6 + 2H2O

• Hydrofluoric acid breaks up the SiO2 structures of silicate based glasses.

• Easy soluble silicon hexaflourid SiF6 (hexafluoro silcia) is formed during the reaction.


Material Science II

Chemical resistance of glass against aqueous acids

Attack by aqueous acids: ion exchange reaction

-Si-O-Na+ + H+ → -Si-OH + Na+

• Gel – layer at the surface which is proton saturated• This gel layer serves as a diffusion barrier. • The thicker this gel-layer the more difficult for ions (Na+, H+) to diffuse through

this layer. -> Passivation!

Distance from the surface

Leaching time


Material Science II

-Si-O-Si- + X-OH→ -Si-OH + SiO-X (X=Li, Na, K)

• Bases attack directly in a detrimental way the network of the glass in contrast to acids. Bases destroy the network.

• The SiO2 molecules are dissolved and remain in the solution as poly-silicates.

• No protection layer is formed in this type of corrosion process

• BUT always a new surface forms which is continuously attacked by the hydroxide-ions of the solution.

Chemical resistance of glass against bases


Material Science II

Chemical resistance of glass against water and combined acid / base exposure

• Pure water at pH 7-9 corrodes glass because of free protons (H3O+) by auto protolysis.

• The glass corrodes by leach-out of alkaline cat ions.

• The alkaline cat ions increase the pH of the water by formation of hydroxyl ions (OH-).

• The hydroxyl ion start to solubilise the glass network and /or the gel layer.

• Thus, hydroxyl ions are consumed, and the proton concentration in the solution increases and the cycle starts over.


Material Science II

Time dependence of glass corrosion

• Type I:• A surface layer is formed which acts as a protection layer

(adsorption protection layer).

• vitreous silica in neutral salt solution accounts for this type.

• Type II:• A protection layer is formed by leaching out of alkalines. The glass network

remains stable.

• Attack of acids at silicate glasses accounts for this type.

• Type III: • Leaching and reaction at the surface form two protection layers of different

composition.

• The glass network remains stable.


Material Science II


• Type IV: • Leaching and wear (material removal) take place at the same time.

• A new leached out layer is formed at the surface which will be continouslyshifted more and more inside the bulk glass by the wear of the glass network (i.e. material removal).

• Alkalisilicate glasses in water account for this type.

• Type V: • Constant wear of the glass network and material removal.

• No leaching layer is formed!

• Hydofluoric acid and strong base attack at silicate glasses account for this type.


Material Science II


tdc tedt

α−∝

c t∝

c t∝

dc adt

=

dc atdt

=

Case 1: For the types I, II and III corrosion stops after formation of a protection layer (passivation), i.e. the corrosion front c moves on with a decreasing speed.

Case 2: For type IV corrosion involves two competing reactions:

(2) the dissolution:

Case 3: For type V reaction or corrosion rate has a constant value:

Case 4: progressive corrosion takes place when we have the solution deficiency on the glass surface. Then, the corrosion reaction changes the pH-value of the solution which leads to a “stronger” corrosion at a higher rate. The wear or corrosion rate increases with reaction time:

(1) the diffusion:


Material Science II

Reaction progress for the corrosion of glasses

Reaction rates for the different cases.

constant (Fall 3)

passivated (Case 1)

progressive (Case 4)

limited (Case 2)

time t


Material Science II

Transmission of a light beam through glass

Way of a light beam transmitting a interface of two media (air, glass)

glass

transmitted light

airair

reflected light

incidentlight beam

reflected light


Material Science II

Influence of Alkaline content on the refractive index nD

Variation to the refractive index as a function of the alkaline content of binary alkalisilicate glasses.


Material Science II

Influence of the network former on the refractive index

Variation of the refractive index nD of a Na2O - SiO2 - glass (20-80 weight%) if SiO2 (network former) is substituted according to weight by other network former (Al2O3, B2O3) or elements.


Material Science II

Fraunhofer Lines

706.52656.27643.85587.56546.07486.13479.99435.84404.66

He red

H red

Cdred

He yellow

Hg green

Hblue

Cdblue

Hg blue

Hg purple

rCC‘deFF‘gh


Material Science II

What is Dispersion?

706.52

656.27

643.85587.56546.0

7486.1

3479.9

9435.8

4404.6

6

He red

H red

Cdred

He yellow

Hg green

Hblue

Cdblue

Hg blue

Hg purple

rCC‘deFF‘gh

Dispersion splits white light in its colours !!!!That effect is fatal for optical applications of glass!!!

The dependence of the refractive index from the light-wavelength.

white light

prismscreen


Material Science II

What is Dispersion?The dependence of the refractive index from the light-wavelength.

706.52

656.27

643.85587.56546.0

7486.1

3479.9

9435.84404.66

He red

H red

Cdred

He yellow

Hg green

Hblue

Cdblue

Hg blue

Hg purple

rCC‘deFF‘gh

νnd 1–

nF nC–-----------------=

ϑ re ln F nC–nD 1–

-----------------=


Material Science II

Dispersion und Refractive index

nD-ν-Diagram of optical glasses

Flint glasses

Crown glasses

νnd 1–

nF nC–-----------------=


Material Science IIDispersion and Refractive Index

nD-ν-Diagramm optischer Gläser

νnd 1–

nF nC–-----------------=


Material Science II

Chromatic Aberration

Chromatic aberration in case of a bi-convex and bi-concave lens.


Material Science II

Achromatic Lens

Flint GlassCrown Glass

Correction of the chromatic aberration by combining two suitable lenses.


Material Science II

Transmission through Glass

Transmissions spectrum of a commercial float glass (thickness 1mm)

Tra

nsm

issi

on

Wave Length

Wave Number


Material Science II

UV-Rim in Glasses

UV rim of glasses of various composition1: SiO2-Glass very pure, 2: SiO2-Glass normal, 3: Na2O - 3 SiO2 Glass very pure, 4: Na2O-3 SiO2-Glass, normal

Tran

smis

sion

Wave Length


Material Science II

Transmission spectrum of Glasses I

Transmission spectra of coloured glasses.

Spec

tral T

rans

mis

sion

τ(λ

)

Wave Length λ [nm]


Material Science II

Transmission spectrum of Glasses II

Transmission spectra of colored glasses.


Material Science II

Colorizing Ions and their Effect I

yellow6Fe(III)blue6Fe(II)

purple6Mn(III)colorless6Mn(II)yellow6Cr(VI)green6Cr(III)

colorless4V(V)green6V(III)purple6Ti(III)ColorCoordinationValency


Material Science II

Colorizing Ions and their Effect II

blue6Cu(II)colorless?Cu(I)yellow6Ni(II)blue4Ni(II)green4Co(III)pink6Co(II)blue4Co(II)

ColorCoordinationValency


Material Science II

Float Glass Process

http://www.glasswebsite.com


Material Science II The Float Glass Process

http://www.glasswebsite.com/video/fgmd.asp


Material Science II

Float Glass process


Material Science II

Float Glass Process

Raw Materials

Batch Charger Furnace

Tin Bath (Float Furnace) Annealing Lehr Cutting System


Material Science II

Composition of commercial float glass

-1.0Others-1.0Alumina (Al2O3)

Working & weathering properties4.0Dolomite(CaMg(CO)2)

Durability8.4Limestone (CaCO3)Easier melting13.0Soda Ash (Na2CO3)-72.6Sand (SiO2)

Reason for AddingGlass CompositionMaterial


Material Science II

Composition Float Glass

http://www.pilkington.com


Material Science II

Chemistry of Glass


Material Science II

Glass-Ceramics

• Structure

• Nucleation and crystal growth

• Fabrication

• Examples

• next: mechanical properties of ceramics (J. Kübler, EMPA)


Material Science II

Glass-Ceramics

• „Glass-ceramic“ refers to materials which are fabricated from glass melts by a process of controlled crystalisation.

• Glass-ceramis is a partially crystalline material which is fabricated by an incomplete crystallisation („Ceraming“) of suitable glasses.

• Brands: Ceran, Zerodur, Robax, Neoceram, Macor


Material Science II

Glass-Ceramics

GlassShort-range order

Grain with grain boundary

SiO4tetrahedron

Si4+

O2-

O2-O2-O2-


Material Science II

Nucleation energy and radius of the nucleus

Dependence of the nucleation energy from its nucleus‘ radius

r

Glass (amorph) to Crystal Energy ∝ r3

Surface Energy = r2


Material Science II

Critical Nucleus Radius

3 24 43

G r G rνπ π σΔ = Δ +

( )2

3

2

16 43 3

G rGν

π σ π σ∗ ∗Δ = =Δ

1( )( )S

r TT T

∗

−∼

2

1( )( )S

G TT T

∗Δ−

∼

-> 1. Derivative must be zero for r*


Material Science II

Nuclei Formation Rate (Nucleation Rate)

( )expKBE GN

kTνν ν∗⎛ ⎞+ Δ

= −⎜ ⎟⎝ ⎠


Material Science II

Crystal Growth Rate (KG)

[ ]'' expG E

N NkT

ν⎛ ⎞Δ +

= ⋅ ⋅ −⎜ ⎟⎝ ⎠

' exp EN NkT

ν ⎛ ⎞= ⋅ ⋅ −⎜ ⎟⎝ ⎠

0 0 1( ' '') exp expKG

GN N Ea aN kT kT

ν ν⎡ ⎤⎛ ⎞Δ⎡ ⎤− ⎛ ⎞= = ⋅ ⋅ − ⋅ − −⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦ ⎢ ⎥⎝ ⎠⎣ ⎦

Crystal Growth Rate


Material Science II

Temperature Dependence of νKB and νKG

Temperature Dependence of νKB and νKG; TE: Freezing Temperature TS: Melting Temperature

KB, Nucleation

KG, Crystal Growth

Nucleation and Crystal Growth rate

TE

TS


Material Science IITemperature-Time (T-t)-Curve for the

Fabrication of a typical Glass-Ceramics

Mel

t

Form

ing

Coo

ling

Che

ckin

g, S

hapi

ng

Nuc

leat

ion

Cry

stal

lisat

ion

Che

ckin

g, S

hapi

ng

Time


Material Science II

Examples for Glass-Ceramic-Systems

bioceramics (dental implants, bone substitutes)8 - 12Phlogopite(Na,K)

Mg3AlSi3O10F2

fabrication of microstructures12Lithium-disilicateLi2O- 2 SiO2

car exhaust filter, substrates for microelectronics, composite materials

1.5 - 3Cordierite2 MgO- 2 Al2O3 –5 SiO2

plates11NephelineNa2O - Al2O3 - 2 SiO2

fireproof cookware, heat exchanger1.5 - 2ß-SpodumeLi2O - Al2O3 - n SiO2,

n= 4-10

cooktop, fireproof cookware fire protection glass, reflecting telescope, gyroscope

0 - 0.7H- Quartz mixed crystal

Li2O-Al2O3- n SiO2, n= 4-6

ApplicationTEC 10-7 K

CrystallinePhaseSystem


Material Science II

Properties of Glass-Ceramics

• thermal expansion: -20 to 200·10-7 K-1

• strength: 60 – 600 MPa

• optical property: transparency – opaque

• chemical resistance: water soluble – inert

• electrical property: semi-conducting – isolating

• mech. machinability: brittle – machinable


Material Science II

Fabrication of Ceran cooktop panels (Schott)

1st step

2nd step


Material Science II

Advantages of glass-ceramicsover ordinary ceramics

Advantages:

• forming is as simple as in case of glass

• transparent pre-forms

• good reproducibility of thematerials properties

• free of pores

• mono-size crystals

• economic fabrication process

Disadvantages:

• limited to certain crystalline phases


Material Science II

Summarizing: Glass & Glass Ceramics

• Glass can be regarded as frozen melt (liquid) - which solidified without crystallisation- which has a short range order but no long-range order.

• The glass structure can be described using Zachariasen‘s network model.

• Glass solidifies at the glass transition temperature Tg, - for T > Tg glass is a (liquid) melt, - for T <Tg glass is a solid.

• The viscosity as a function of temperature is a smooth (steady) curve spanning a range of 16 to 18 orders of magnitude.

• Glass-ceramics is fabricated from glass by using controlled crystallisation process, and it has special properties.


Material Science II

Ersatz


Material Science IIOverview on the composition of

important glass types

25303213––––––––––chalcogenideglass 2

–335512––––––––––chalcogenideglass 1

––––1315410-1691,540enamel

––––---1017,54,5--1454E-glass

––––---12,5--0,54380Laboratory glass

––––--17,5---122,5860lead crystal glass

––––----8,53,5-13,51,572float glass

––––----10--14272Kalk-Natron-glass(ordinary glass)

–––––––––––––100quartz glass

TeGeSeAsFTiO2PbOB2O3CaOMgOK2ONa2OAl2O3SiO2Glass type

All amounts in weight -%.http://de.wikipedia.org/wiki/Glas#Einstellung_der_Glaseigenschaften


Material Science II


Material Science II

The basic idea of the float glass process

• Molten glass poured onto a bath of clean molten tin, will spread out in the same way that oil will spread out if poured onto a bath of water.

• Gravity and surface tension will result in the top and bottom surfaces of the glass becoming approximately flat and parallel.


Material Science II

The basic idea of the float glass process

2 2( )( )

tg gt t

g t g

T S S Sg

ρρ ρ ρ

= + +−

i

where Sg, Sgt, and St are the values of surface tension at the three interfaces.

The equilibrium thickness (T)

For standard soda-lime-silica glass under a protective atmosphere and on clean tin the equilibrium thickness is approximately 7 mm.


Material Science II

The Production Process

Material Science II Ceramic Materials Chapter 5: Glass 5: Glass. Ceramics ... Chap 5 slide 2...

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