material science ii ceramic materials chapter 5: glass 5: glass. ceramics ... chap 5 slide 2...
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slide 1Ceramics: Glass, Chap 5
Material Science II
Ceramic Materials
F. Filser & L.J. GaucklerETH-Zürich, Departement Materials
SS 2007
Chapter 5: Glass
slide 2Ceramics: Glass, Chap 5
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]
slide 3Ceramics: Glass, Chap 5
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
slide 4Ceramics: Glass, Chap 5
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
slide 5Ceramics: Glass, Chap 5
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
slide 6Ceramics: Glass, Chap 5
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
slide 7Ceramics: Glass, Chap 5
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
slide 10Ceramics: Glass, Chap 5
Material Science II
Bragg diffraction of glassy and crystalline material (PbF2)
slide 11Ceramics: Glass, Chap 5
Material Science II
Laue-Diagram for a Single Crystal
(Points)
single crystal
aperture
film
slide 12Ceramics: Glass, Chap 5
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)
slide 13Ceramics: Glass, Chap 5
Material Science II
[SiO4] - Network
[SiO4] - network with network modifiers Na and Ca
slide 14Ceramics: Glass, Chap 5
Material Science II
Glass
GlassShort range order = Tetrahedron
[SiO4]4-
TetrahedronSi4+
O2-
O2-O2-O2-
z.B. Na+,K+
O2- Si4+
Si4+
O2-
slide 15Ceramics: Glass, Chap 5
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.
slide 16Ceramics: Glass, Chap 5
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
slide 17Ceramics: Glass, Chap 5
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
slide 18Ceramics: Glass, Chap 5
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)
slide 19Ceramics: Glass, Chap 5
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)
slide 20Ceramics: Glass, Chap 5
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
slide 21Ceramics: Glass, Chap 5
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
slide 22Ceramics: Glass, Chap 5
Material Science II
Elongation of Glass I
Dilatometry for the determination of Tg and α of a glass.
1/th ollT
α Δ=
Δi
slide 23Ceramics: Glass, Chap 5
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
slide 24Ceramics: Glass, Chap 5
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
slide 25Ceramics: Glass, Chap 5
Material Science II
Density as function of the alkali amount
Density of binary alkalisilicate glasses
slide 26Ceramics: Glass, Chap 5
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.
slide 27Ceramics: Glass, Chap 5
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
slide 28Ceramics: Glass, Chap 5
Material Science IIPre-stressing
Stress profiles for the a) thermal and the b) chemical method of pre-stressing.
a) b)
tension compression
surface
surface
slide 29Ceramics: Glass, Chap 5
Material Science II
Chemical Resistance of Glasses
• hydrofluoric acid HF attack (corrosion)
• diluted aqueous acids attack
• base attack
• combined water and acid / base attack
slide 30Ceramics: Glass, Chap 5
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.
slide 31Ceramics: Glass, Chap 5
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
slide 32Ceramics: Glass, Chap 5
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
slide 33Ceramics: Glass, Chap 5
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.
slide 34Ceramics: Glass, Chap 5
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.
slide 35Ceramics: Glass, Chap 5
Material Science II
Time dependence of glass corrosion
• 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.
slide 36Ceramics: Glass, Chap 5
Material Science II
Time dependence of glass corrosion
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:
slide 37Ceramics: Glass, Chap 5
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
slide 38Ceramics: Glass, Chap 5
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
slide 39Ceramics: Glass, Chap 5
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.
slide 40Ceramics: Glass, Chap 5
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.
slide 41Ceramics: Glass, Chap 5
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
slide 42Ceramics: Glass, Chap 5
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
slide 43Ceramics: Glass, Chap 5
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–
-----------------=
slide 44Ceramics: Glass, Chap 5
Material Science II
Dispersion und Refractive index
nD-ν-Diagram of optical glasses
Flint glasses
Crown glasses
νnd 1–
nF nC–-----------------=
slide 45Ceramics: Glass, Chap 5
Material Science IIDispersion and Refractive Index
nD-ν-Diagramm optischer Gläser
νnd 1–
nF nC–-----------------=
slide 46Ceramics: Glass, Chap 5
Material Science II
Chromatic Aberration
Chromatic aberration in case of a bi-convex and bi-concave lens.
slide 47Ceramics: Glass, Chap 5
Material Science II
Achromatic Lens
Flint GlassCrown Glass
Correction of the chromatic aberration by combining two suitable lenses.
slide 48Ceramics: Glass, Chap 5
Material Science II
Transmission through Glass
Transmissions spectrum of a commercial float glass (thickness 1mm)
Tra
nsm
issi
on
Wave Length
Wave Number
slide 49Ceramics: Glass, Chap 5
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
slide 50Ceramics: Glass, Chap 5
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]
slide 51Ceramics: Glass, Chap 5
Material Science II
Transmission spectrum of Glasses II
Transmission spectra of colored glasses.
slide 52Ceramics: Glass, Chap 5
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
slide 53Ceramics: Glass, Chap 5
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
slide 55Ceramics: Glass, Chap 5
Material Science II The Float Glass Process
http://www.glasswebsite.com/video/fgmd.asp
slide 57Ceramics: Glass, Chap 5
Material Science II
Float Glass Process
Raw Materials
Batch Charger Furnace
Tin Bath (Float Furnace) Annealing Lehr Cutting System
slide 58Ceramics: Glass, Chap 5
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
slide 59Ceramics: Glass, Chap 5
Material Science II
Composition Float Glass
http://www.pilkington.com
slide 61Ceramics: Glass, Chap 5
Material Science II
Glass-Ceramics
• Structure
• Nucleation and crystal growth
• Fabrication
• Examples
• next: mechanical properties of ceramics (J. Kübler, EMPA)
slide 62Ceramics: Glass, Chap 5
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
slide 63Ceramics: Glass, Chap 5
Material Science II
Glass-Ceramics
GlassShort-range order
Grain with grain boundary
SiO4tetrahedron
Si4+
O2-
O2-O2-O2-
slide 64Ceramics: Glass, Chap 5
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
slide 65Ceramics: Glass, Chap 5
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*
slide 66Ceramics: Glass, Chap 5
Material Science II
Nuclei Formation Rate (Nucleation Rate)
( )expKBE GN
kTνν ν∗⎛ ⎞+ Δ
= −⎜ ⎟⎝ ⎠
slide 67Ceramics: Glass, Chap 5
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
slide 68Ceramics: Glass, Chap 5
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
slide 69Ceramics: Glass, Chap 5
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
slide 70Ceramics: Glass, Chap 5
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
slide 71Ceramics: Glass, Chap 5
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
slide 72Ceramics: Glass, Chap 5
Material Science II
Fabrication of Ceran cooktop panels (Schott)
1st step
2nd step
slide 73Ceramics: Glass, Chap 5
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
slide 74Ceramics: Glass, Chap 5
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.
slide 76Ceramics: Glass, Chap 5
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
slide 78Ceramics: Glass, Chap 5
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.
slide 79Ceramics: Glass, Chap 5
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.