8/14/2019 Kuliah_10_KXEX 1110

1/43

CHAPTER

10Applications and Processing of

Ceramics

8-1

8/14/2019 Kuliah_10_KXEX 1110

2/43

Fabrication and Processing of Ceramics

8/14/2019 Kuliah_10_KXEX 1110

3/43

Glass

Combination of transparency, strength, hardness and

corrosion resistance.

Glass is an inorganic product of fusion that has cooled to a

rigid condition without crystallization.

Glass does not crystallize

up on cooling.

Up on cooling, it transforms

from rubbery material to

rigid glass.

Figure 10.52

11-40

8/14/2019 Kuliah_10_KXEX 1110

4/43

Glass Structure

Quartz is crystalline

SiO2:

Basic Unit: Glass is amorphous

Amorphous structureoccurs by adding impurities

(Na+,Mg2+,Ca2+, Al3+)

Impurities:

interfere with formation ofcrystalline structure.

(soda glass)

Si04 tetrahedron4-

Si4+

O2-

Si4+

Na+

O2-

8/14/2019 Kuliah_10_KXEX 1110

5/43

In cristobalite, Si-O tetrahedron are joined corner to

corner to form long range order.

In simple silica glass, tetrahedra are joined corner to

corner to form loose network.

8/14/2019 Kuliah_10_KXEX 1110

6/43

Composition of Glass

Soda lime glass: Very common glass (90%).

71-73% SiO2, 12-14% Na2O, 10-12% CaO.

Easier to form and used in flat glass and containers.

Borosilicate glass: Alkali oxides are replaced by boric oxide in silica

glass network.

Known as Pyrex glass and is used for lab equipments andpiping.

Lead glass: Lead oxide acts as network modifier and network former.

Low melting point used for solder sealing.

Used in radiation shields, optical glass and TV bulbs.

8/14/2019 Kuliah_10_KXEX 1110

7/43

Glass Modifying Oxides and Intermediate Oxides

Network modifiers: Oxides thatbreakup the glass

network.

Added to glass to increase workability.

Examples:- Na2O, K2O, CaO, MgO.

Oxygen atom enters network and other ion stayin interstices.

Intermediate oxides: Cannot form glass network by

themselves but canjoin into an existing network.

Added to obtain special properties.Examples: Al2O3, Lead oxide.

8/14/2019 Kuliah_10_KXEX 1110

8/43

Glass Properties

Specific volume (1/) vs Temperature (T):

Glasses:-- do not crystallize

-- change in slope in spec. vol. curve at

glass transition temperature, Tg-- transparent

- no crystals to scatter light

Crystalline materials:-- crystallize at melting temp, Tm-- have abrupt change in spec.

vol. at Tm

Adapted from Fig. 13.6, Callister, 7e.

T

Specific volume

SupercooledLiquid

solid

Tm

Liquid(disordered)

Crystalline(i.e., ordered)

Tg

Glass

(amorphous solid)

8/14/2019 Kuliah_10_KXEX 1110

9/43

Viscosity

Viscosity, :-- relates shear stress and velocity gradient:

has units of (Pa-s)

y

v

d

d=

velocity gradient

dv

dy

glass dvdy

8/14/2019 Kuliah_10_KXEX 1110

10/43

Viscous Deformation of Glass

Viscosity decreases with T

Impurities lowerTdeformfused

silica

96%si

lica

soda-lime

glass

Visco

sity[Pa

s]

1

102

10

6

1010

1014

200 600 1000 1400 1800 T(C)

Tdeform : soft enoughto deform or work

annealing range

Pyr

ex

Tmelt

strain point

fused silica: > 99.5 wt% SiO2

soda-lime glass: 70% SiO2

balance Na2O (soda) & CaO (lime)

Vycor: 96% SiO2, 4% B2O3

borosilicate (Pyrex):

13% B2O3, 3.5% Na2O, 2.5% Al2O3

8/14/2019 Kuliah_10_KXEX 1110

11/43

Viscous above Tg and viscosity decreases with increase in temperature.

* = 0e+Q/RT *= Viscocity of glass (PaS)

0= preexponential constant (PaS)

Q = Activation energy

Working point: 103 PaS glass

fabrication can be carried out

Softening point: 107 PaS glass

flows under its own weight.

Annealing point: 1012 PaS Internal

stresses can be relieved..

Strain point: 10 13.5 PaS glass is

rigid below this point.

Figure 10.55

8/14/2019 Kuliah_10_KXEX 1110

12/43

Forming Methods

Forming sheet and plate

glass:Ribbon of glass moves

out of furnace and floatson abath of molten tin.

Glass is cooled by moltentin.

After it is hard, it isremoved and passedthrough a long annealing

furnace.

8/14/2019 Kuliah_10_KXEX 1110

13/43

Blowing

Blowing: Air blown to force molten glass into molds.

suspendedParison

Finishingmold

Compressedair

8/14/2019 Kuliah_10_KXEX 1110

14/43

Pressing

Pressing: Optical and sealed beam lenses are

pressed by aplungerinto a mold containing

molten glass.

Gob

Parison

mold

Pressing

operation

8/14/2019 Kuliah_10_KXEX 1110

15/43

Casting

Casting: Molten glass is cast in open mold.

Centrifugal casting: Glass globs are dropped into

spinning mold.

Glass first flows outward towards wall of mold and

then upward against the mold wall.

8/14/2019 Kuliah_10_KXEX 1110

16/43

Drawing

Continuous drawing

originally sheet glass was made by floating glass

on a pool of mercury

plates, dishes, cheap glasses

--mold is steel with

graphite lining

Fiber drawing:

wind up

8/14/2019 Kuliah_10_KXEX 1110

17/43

8/14/2019 Kuliah_10_KXEX 1110

18/43

Chemically Strengthened Glass

Special treatment increases chemical resistance of

glasses.

Example:- Sodium aluminosilicate glasses are

immersed in a bath of potassium nitrate at 500C

for 6 to 10 hoursLarge potassium ions are induced into surface

causing compressive stress.

Compressive layer is much thinner than that in

thermal tempering. Used for supersonic aircraft glazing and

ophthalmic lenses.

8/14/2019 Kuliah_10_KXEX 1110

19/43

Heat Treating Glass

Annealing:

--removes internal stress caused by uneven cooling. Tempering:

--puts surface of glass part into compression

--suppresses growth of cracks from surface scratches.

--sequence:

further cooled

tension

compression

compression

before cooling

hot

surface cooling

hot

cooler

cooler

--Result: surface crack growth is suppressed.

8/14/2019 Kuliah_10_KXEX 1110

20/43

2. Particulate Forming

8/14/2019 Kuliah_10_KXEX 1110

21/43

Traditional Ceramics

A mixture of components used

(50%) 1. Clay

(25%) 2. Filler e.g. quartz (finely ground)

(25%) 3. Fluxing agent (Feldspar)

binds it together

aluminosilicates + K+, Na+, Ca+

8/14/2019 Kuliah_10_KXEX 1110

22/43

Traditional Ceramics

Clay: Provide workability and hardness.

Silica: Provide better temperature resistance and MP.

Potash Fledspar: Makes glass when ceramic is fired.

Quartz

grain High-silica

glass

8/14/2019 Kuliah_10_KXEX 1110

23/43

Engineering Ceramics

Alumina (Al2O3): Aluminum oxide is doped with

magnesium oxide, cold pressed and sintered. Uniform structure. Used for electric applications.

Silicon Nitride (Si3N4): Compact of silicon powder is

nitrided in a flow of nitrogen gas.

Moderate strength and used for parts of advanced engines.

Silicon Carbide (SiC):Very hard refractory carbide,sintered at 21000C.

Used as reinforcement in composite materials.

Zirconia (ZrO2): Polymorphic and is subject to cracking.

Combined with 9% MgO to produce ceramic with high

fracture toughness.

8/14/2019 Kuliah_10_KXEX 1110

24/43

Hydroplastic Forming

Milling and screening: desired particle size Mixing particles & water: produces a "slip" Form a "green" component

Dry and fire the component

ram billet

container

containerforce

die holder

die

Ao

Adextrusion--Hydroplastic forming:

extrude the slip (e.g., into a pipe)

Adapted from

Fig. 11.8 (c),

Callister 7e.

solid component

--Slip casting:Adapted from Fig.

13.12, Callister 7e.

(Fig. 13.12 is from

W.D. Kingery,

Introduction to

Ceramics, John

Wiley and Sons,

Inc., 1960.)

hollow component

pour slipinto mold

drain

moldgreenceramic

pour slipinto mold

absorb waterinto mold

greenceramic

8/14/2019 Kuliah_10_KXEX 1110

25/43

Feature of Slip

Clay is inexpensive Adding water to clay-- allows material to shear easily

along weak van der Waals bonds

-- enables extrusion

-- enables slip casting

Structure of

Kaolinite Clay:

weak vander Waalsbonding

chargeneutral

chargeneutral

Si 4+

Al3+

-OH

O2-

Shear

Shear

8/14/2019 Kuliah_10_KXEX 1110

26/43

Drying and Firing

Drying: layer size and spacing decrease.Adapted from Fig.

13.13, Callister 7e.

(Fig. 13.13 is from

W.D. Kingery,Introduction to

Ceramics, John

Wiley and Sons,

Inc., 1960.)

Drying too fast causes sample to warp or crack due to non-uniform shrinkage

wet slip partially dry green ceramic

Firing:--Traised to (900-1400C)

--vitrification: liquid glass forms from clay and flows between

SiO2 particles. Flux melts at lowerT.Adapted from Fig. 13.14,

Callister 7e.(Fig. 13.14 is courtesy H.G.

Brinkies, Swinburne

University of Technology,

Hawthorn Campus,

Hawthorn, Victoria,

Australia.)

Si02 particle(quartz)

glass formedaroundthe particle

micrograph ofporcelain

70m

8/14/2019 Kuliah_10_KXEX 1110

27/43

Powder Pressing

Sintering - powder touches - forms neck & gradually

neck thickens add processing aids to help form neck

little or no plastic deformation

Uniaxial compression - compacted in single direction

Isostatic(hydrostatic) compression - pressure applied byfluid - powder in rubber envelope

Hot pressing - pressure + heat

8/14/2019 Kuliah_10_KXEX 1110

28/43

Sintering: useful for both clay and non-clay compositions.

Procedure:-- produce ceramic and/or glass particles by grinding-- place particles in mold

-- press at elevated Tto reduce pore size.

Aluminum oxide powder:

-- sintered at 1700Cfor 6 minutes.

15m

8/14/2019 Kuliah_10_KXEX 1110

29/43

Tape Casting

thin sheets of green ceramic cast as flexible tape

used for integrated circuits and capacitors

cast from liquid slip (ceramic + organic solvent)

8/14/2019 Kuliah_10_KXEX 1110

30/43

Cementation

Produced in extremely large quantities.

Portland cement:-- mix clay and lime bearing materials

-- calcinate (heat to 1400C)

-- primary constituents:

tri-calcium silicate

di-calcium silicate

Adding water-- produces a paste which hardens

-- hardening occurs due to hydration (chemical reactions

with the water). Forming: done usually minutes after hydration begins.

8/14/2019 Kuliah_10_KXEX 1110

31/43

8-2

Glasses Clay

products

Refractories Abrasives Cements Advanced

ceramics

-optical-compositereinforce

-containers/household

-whiteware-bricks

-bricks forhigh T(furnaces)

-sandpaper-cutting-polishing

-composites-structural

engine-rotors-valves-bearings

-sensors

Ceramics

8/14/2019 Kuliah_10_KXEX 1110

32/43

Refractories

Need a material to use in high temperature furnaces.

Consider the Silica (SiO2) - Alumina (Al2O3) system.

Phase diagram shows:

mullite, alumina, and crystobalite as candidate

refractories.

Composition (wt% alumina)

T(C)

1400

1600

1800

2000

2200

20 40 60 80 1000

alumina +mullite

mullite

+ L

mulliteLiquid

(L)

mullite + crystobalite

crystobalite+ L

alumina + L

3Al2O3-2SiO2

8/14/2019 Kuliah_10_KXEX 1110

33/43

Acidic refractories:

Silica refractories have high mechanical strengthand rigidity.

Fireclays: Mixture of plastic fireclay, flint clay andgrog. Particles vary from coarse to very fine.

High aluminum refractories: Contain 50-90%alumina and have higher fusion temperature.

Basic refractories: consists mainly of MgO andCaO.

Have high bulk densities, melting temperature andresistance to chemical attack.

used for lining in basic-oxygen steelmaking process.

8/14/2019 Kuliah_10_KXEX 1110

34/43

8/14/2019 Kuliah_10_KXEX 1110

35/43

Cutting Tools

Tools:

-- for grinding glass, tungsten,carbide, ceramics

-- for cutting Si wafers

-- for oil drilling

bladesoil drill bits

Solutions:

coated single

crystal diamonds

polycrystalline

diamonds in a resin

matrix.

-- manufactured single crystalor polycrystalline diamonds

in a metal or resin matrix.

-- optional coatings (e.g., Ti to help

diamonds bond to a Co matrix

via alloying)-- polycrystalline diamonds

resharpen by microfracturing

along crystalline planes.

8/14/2019 Kuliah_10_KXEX 1110

36/43

Sensors

Example: Oxygen sensor ZrO2

Principle: Make diffusion of ionsfast for rapid response.

A Ca2+ impurity

removes a Zr4+ and a

O2- ion.

Ca2+

Approach:

Add Ca impurity to ZrO2:

-- increases O2- vacancies

-- increases O2- diffusion rate

referencegas at fixedoxygen content

O2-

diffusion

gas with anunknown, higheroxygen content

-+voltage difference produced!

sensor Operation:

-- voltage differenceproduced when

O2-

ions diffusefrom the external

surface of the sensor

to the reference gas.

8/14/2019 Kuliah_10_KXEX 1110

37/43

Insulation

About 70% of external surface is protected from heat by

24000 ceramic tiles. Material: Silica fiber compound.

Density is 4kg/ft3 and withstands temperature up to

12600C.

Figure 10.51

8/14/2019 Kuliah_10_KXEX 1110

38/43

Ceramic Insulator Materials

Ionic and covalent bonding restricts the mobility of ions and electrons

and hence ceramics are good insulators.

Electrical porcelain: 50% Clay + 25 % Fledspar.

Good plasticity, wider firing temperature range, cheap.

High power loss factor.

Steatite: 90% talc + 10 % clay

Good insulator, low power loss factor, impact strength

Fosterite: Mg2SiO4 no alkali ions

Higher resistivity, low electrical loss

Alumina: Al2O3 Crystalline phase bounded to glassy

matrix.

High dielectric strength, low dielectric loss

8/14/2019 Kuliah_10_KXEX 1110

39/43

Capacitors

Ceramics are used as dielectric materials

for capacitors.

Example: Disk ceramic capacitors. BaTiO3 + additive

Very high dielectric

constant

Used in ceramic based

thick film hybridelectronic circuit

Higher capacitance per unit area

Figure 10.38a

8/14/2019 Kuliah_10_KXEX 1110

40/43

Semiconductors

Ceramics can be used as semiconducting materials.

Thermistor: Thermally sensitive resistor.

NTC thermistor: Conductivity raises with temperature.

Solid solution oxides of Mn, Ni, Fe, Co and Cu are used

to obtain necessary property ranges.

By combining low conducting metal oxide with low

conducting oxides intermediate properties are obtained.

Example: Conductivity of Fe3O4 is reduced gradually by

adding increasing amounts in solid solution of MgCr2O4

8/14/2019 Kuliah_10_KXEX 1110

41/43

Electronic Packaging

Chosen to securely hold microelectronics & provideheat transfer

Must match the thermal expansion coefficient of themicroelectronic chip & the electronic packaging

material. Additional requirements include: good heat transfer coefficient

poor electrical conductivity

Materials currently used include:

Boron nitride (BN) Silicon Carbide (SiC)

Aluminum nitride (AlN)

thermal conductivity 10x that for Alumina

good expansion match with Si

8/14/2019 Kuliah_10_KXEX 1110

42/43

8/14/2019 Kuliah_10_KXEX 1110

43/43

Ceramic ArmorAl2O3, B4C, SiC & TiB2

Extremely hard materials

shatter the incoming projectile

energy absorbent material underneath