applications and processing of ceramics - imeng.ndhu.edu.t file4 applications and processing of...

CHAPTER

13

Applications and

Processing of Ceramics

1

4

Applications and Processing of Ceramics

ISSUES TO ADDRESS...

• How do we classify ceramics?

• What are some applications of ceramics?

• How is processing of ceramics different than for metals?

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics

Fabrication and processing of glasses and glass-ceramics

Fabrication and processing of clay products

Powder pressing

Tape casting

5

6

Glasses Clay

products

Refractories Abrasives Cements Advanced

ceramics

-optical

- composite reinforce

- containers/ household

-whiteware

- structural

-bricks for high T

(furnaces)

-sandpaper

- cutting - polishing

-composites

- structural

-engine

rotors valves

bearings -sensors

Classification of Ceramics

Ceramic Materials

Fireclay

Silica

Basic

Special

Traditional Ceramics

• Made up of clay, silica and feldspar

• Clay: Provide workability and

hardness.

• Silica: Provide better temperature

resistance and MP.

• Potash Feldspar: Makes glass when

ceramic is fired.

SEM of Porcelain

Quartz

grain High-silica

glass Figure 11.35

Source: F. Norton, Elements of Ceramics, 2nd ed., Addision-Wesley,1974, p.140. 7

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

Insulation for Space Shuttle Orbital

• 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

• Space Shuttle Columbia disaster occurred on February 1, 2003

• Space Shuttle Challenger disaster occurred on January 28, 1986

Courtesy of NASA 9

10

tensile force

A o

A d die

die

• Die blanks: -- Need wear resistant properties!

• Die surface: -- 4 mm polycrystalline diamond

particles that are sintered onto a

cemented tungsten carbide

substrate.

-- polycrystalline diamond gives uniform

hardness in all directions to reduce

wear.

Adapted from Fig. 11.8(d),

Callister & Rethwisch 8e.

Courtesy Martin Deakins, GE

Superabrasives, Worthington,

OH. Used with permission.

Ceramics Application: Die Blanks

11

• Tools: -- for grinding glass, tungsten,

carbide, ceramics

-- for cutting Si wafers

-- for oil drilling

blades oil drill bits

Single crystal

diamonds

polycrystalline

diamonds in a resin

matrix.

Photos courtesy Martin Deakins,

GE Superabrasives, Worthington,

OH. Used with permission.

Ceramics Application: Cutting Tools

• Materials: -- manufactured single crystal

or polycrystalline diamonds

in a metal or resin matrix.

-- polycrystalline diamonds

resharpen by microfracturing

along cleavage planes.

12

• Example: ZrO2 as an oxygen sensor

• Principle: Increase diffusion rate of oxygen

to produce rapid response of sensor signal to

change in oxygen concentration

Ceramics Application: Sensors

A substituting Ca2+ ion

removes a Zr 4+ ion and

an O2- ion.

Ca 2+

• Approach: Add Ca impurity to ZrO2: -- increases O2- vacancies

-- increases O2- diffusion rate

reference gas at fixed oxygen content

O 2-

diffusion

gas with an unknown, higher oxygen content

- + voltage difference produced!

sensor • Operation: -- voltage difference produced when

O2- ions diffuse from the external

surface through the sensor to the

reference gas surface.

-- magnitude of voltage difference

partial pressure of oxygen at the

external surface

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

13

Glasses

• 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

14

15

• Quartz is crystalline

SiO2:

• Basic Unit: Glass is noncrystalline (amorphous)

• Fused silica is SiO2 to which no

impurities have been added

• Other common glasses contain

impurity ions such as Na+, Ca2+,

Al3+, and B3+

(soda glass)

Glass Structure

Si0 4 tetrahedron 4-

Si 4+

O 2 -

Si 4+

Na +

O 2 -

Structure of Glasses

• Glass-Forming Oxides: Fundamental subunit of glass is

SiO44- tetrahedron. (B2O3)

• Si 4+ ion is covalently ionically bonded to four oxygen atoms.

• 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.

Cristobailite Simple silica glass SiO4

4-

Courtesy of Corning Glass Works 16

Glass Modifying Oxides and Intermediate Oxides

• Network modifiers: Oxides that breakup the glass

network.

Added to glass to increase workability.

Examples:- Na2O, K2O, CaO, MgO.

Oxygen atom enters network and other ion stay

in interstices.

• Intermediate oxides: Cannot form glass network by

themselves but can join into an existing network.

Added to obtain special properties.

Examples: Al2O3, Lead oxide.

17

Composition of Glasses

• 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 and piping.

• 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.

18

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

20

Glass-Ceramics

• Glass-ceramics are initially fabricated as glasses, and

– then, by heat treatment,

– crystallized to form fine-grained polycrystalline

materials

• Two properties of glass-ceramics that make them

superior to glass are

– improved mechanical strengths and

– lower coefficients of thermal expansion

• (which improves thermal shock resistance).

21

22

Continuous cooling transformation of a lunar glass

Clay products

• Clay is the principal component of

– the whitewares

• pottery and tableware

– structural clay products

• building bricks and tiles

• Ingredients (in addition to clay) may be added

– such as feldspar and quartz

– these influence changes that occur during firing

23

24

• Clay is inexpensive

• When water is added to clay -- water molecules fit in between

layered sheets -- reduces degree of van der Waals

bonding -- when external forces applied – clay

particles free to move past one

another – becomes hydroplastic

• Structure of

Kaolinite Clay:

Hydroplasticity of Clay

weak van der Waals bonding

charge neutral

charge neutral

Si 4+

Al 3 +

- OH

O 2-

Shear

Shear

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

25

26

• Materials to be used at high temperatures (e.g., in

high temperature furnaces).

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

• Silica refractories - silica rich - small additions of alumina

depress melting temperature (phase diagram):

Fig. 12.27, Callister &

Rethwisch 8e. (Fig. 12.27

adapted from F.J. Klug and

R.H. Doremus, J. Am. Cer.

Soc. 70(10), p. 758, 1987.)

Refractories

Composition (wt% alumina)

T(ºC)

1400

1600

1800

2000

2200

20 40 60 80 100 0

alumina +

mullite

mullite + L

mullite Liquid

(L)

mullite + crystobalite

crystobalite + L

alumina + L

3Al2O3-2SiO2

Acidic and Basic Refractories

• Acidic refractories:

Silica refractories have high mechanical strength

and rigidity.

Fireclays: Mixture of plastic fireclay, flint clay and

grog. 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 and CaO.

Have high bulk densities, melting temperature and

resistance to chemical attack.

used for lining in basic-oxygen steelmaking process.

28

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

29

Ceramic Abrasive Materials

• Ceramics are hard and can be used as abrasives

for cutting, grinding and polishing

• Examples:- Al2O3, SiC

• Diamond and c-BN are superabrasives

• By combining ceramics, improved abrasives can be

developed

• Example:- 25% ZrO2 + 75% Al2O3

30

Hardness of Selected Materials

0

20

40

60

80

100

Alu

min

um

43

40

Ste

el

To

ol

Ste

el

TiN

TiC

cBN

Su

per

latt

ice

Dia

mo

nd

Ha

rd

ness

, G

Pa

Ultra-hard

Hard

Ha

rdn

ess,

GP

a

Superhard

31

Increasing feed rate

Increa

sing

cuttin

g sp

eed

PCD

CBN

Ceramics

Cermets

Cemented

Carbides

High Speed

Tool Steel

Relative Machining Application ranges of

Cutting Tool Materials

Polycrystalline diamond

Polycrystalline cubic boron nitride

Al2O3, Si3N4, SiAlON

(Ti,Mo/W)CN, (Ti, Mo,/W, Nb,Ta)CN

94WC-6Co, 72WC-8TiC-11.5TaC-8.5Co

32

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

36

Cements

• Portland cement is produced by heating a mixture of clay and

lime-bearing minerals in a rotary kiln.

– The resulting “clinker” is ground into very fine particles to which a

small amount of gypsum is added.

• When mixed with water, inorganic cements form a paste that is

capable of assuming just about any desired shape.

• Subsequent setting or hardening is a result of chemical

reactions involving the cement particles and occurs at the

ambient temperature.

37

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

38

39

Advanced Ceramics:

Materials for Automobile Engines

• Advantages:

– Operate at high temperatures

– high efficiencies

– Low frictional losses

– Operate without a cooling

system

– Lower weights than current

engines

• Disadvantages:

– Ceramic materials are

brittle

– Difficult to remove internal

voids (that weaken

structures)

– Ceramic parts are difficult

to form and machine

• Potential candidate materials: Si3N4, SiC, & ZrO2

• Possible engine parts: engine block & piston coatings

40

Advanced Ceramics:

Materials for Ceramic Armor

Components: -- Outer facing plates

-- Backing sheet

Properties/Materials: -- Facing plates -- hard and brittle

— fracture high-velocity projectile

— Al2O3, B4C, SiC, TiB2

-- Backing sheets -- soft and ductile

— deform and absorb remaining energy

— aluminum, synthetic fiber laminates

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

41

43

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

• Glasses: -- do not crystallize

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

glass transition temperature, Tg

-- transparent - no grain boundaries to

scatter light

• Crystalline materials: -- crystallize at melting temp, Tm

-- have abrupt change in spec.

vol. at Tm

Adapted from Fig. 13.6,


Glass Properties

T

Specific volume

Supercooled Liquid

solid

Tm

Liquid (disordered)

Crystalline (i.e., ordered)

Tg

Glass

(amorphous solid)

44

Glass Properties: Viscosity

• Viscosity, h: -- relates shear stress () and velocity gradient (dv/dy):

h has units of (Pa-s)

dydv /

h

velocity gradient

dv

dy

glass dv

dy

45

Vis

co

sity [P

a-s

]

1

10 2

10 6

10 10

10 14

200 600 1000 1400 1800 T(ºC)

Working range:

glass-forming carried out

annealing point

Tmelt

strain point

• Viscosity decreases with T

Log Glass Viscosity vs. Temperature

• 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

Viscous Deformation of glasses.

• Viscous above Tg and viscosity decreases with increase in

temperature.

η* = η0e+Q/RT η*

η0

= Viscocity of glass (Pa． s)

= preexponential constant (Pa. s)

Q = Activation energy

1. Working point: 103 Pa. s – glass

fabrication can be carried out

2. Softening point: 107 Pa. s – glass

flows under its own weight.

3. Annealing point: 1012 Pa. s – Internal

stresses can be relieved..

4. Strain point: 10 13.5 Pa. s – glass is

rigid below this point.

Figure 10.55

After O. H. Wyatt and D. Dew-Hughes, “Metals Ceramics and Polymers,” Cambridge, 1974, p.259. 46

47

• Blowing of Glass Bottles:

GLASS

FORMING

Ceramic Fabrication Methods (i)

Gob

Parison mold

Pressing operation

Suspended parison

Finishing mold

Compressed air

• Fiber drawing:

wind up

PARTICULATE

FORMING

CEMENTATION

-- glass formed by application of

pressure

-- mold is steel with graphite

lining

• Pressing: plates, cheap glasses

48

Sheet Glass Forming

• Sheet forming – continuous casting

– sheets are formed by floating the molten glass on a pool of molten

tin

49

• Annealing: -- removes internal stresses caused by uneven cooling.

• Tempering: -- puts surface of glass part into compression

-- suppresses growth of cracks from surface scratches.

-- sequence:

Heat Treating Glass

at room temp.

tension

compression

compression

before cooling

hot

initial cooling

hot

cooler

cooler

-- Result: surface crack growth is suppressed.

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

50

Processing of Ceramics

• Produced by compacting powder or particles into shapes and heated to bond particles together

• Agglomeration of particles

• Basic steps in ceramic processing

– Material preparation: Particles and binders and lubricants are (sometimes ground) and blend wet or dry.

– Forming: Formed in dry, plastic or liquid conditions

– Thermal treatment by drying and firing

• Cold forming process is predominant.

• Pressing, slipcasting and extrusion are the common forming processes.

51

52

• Mill (grind) and screen constituents: desired particle size

• Extrude this mass (e.g., into a brick)

• Dry and fire the formed piece

ram billet

container

container force

die holder

die

A o

A d extrusion Adapted from

Fig. 12.8(c),

Callister &

Rethwisch 8e.

Ceramic Fabrication Methods (iia)

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION

Hydroplastic forming:

53

• Mill (grind) and screen constituents: desired particle size

• Slip casting operation

• Dry and fire the cast piece

Ceramic Fabrication Methods (iia)

solid component

Adapted from Fig.

13.12, Callister &

Rethwisch 8e. (Fig.

13.12 is from W.D.

Kingery, Introduction

to Ceramics, John

Wiley and Sons, Inc.,

1960.)

hollow component

pour slip

into mold

drain

mold “green

ceramic”

pour slip into mold

absorb water into mold

“green ceramic”

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION

Slip casting:

• Mix with water and other constituents to form slip

Slip Casting

• Powdered ceramic material and a liquid mixed to

prepare a stable suspension (slip).

• Slip is poured into porous mold and liquid portion is

partially absorbed by mold.

• Layer of semi-hard material

is formed against mold

surface.

• Excess slip is poured out

of cavity or cast as solid

• The material in mold is

allowed to dry and then fired

Figure 10.27

After W. D. Kingery, “ Introduction to Ceramics,” Wiley, 1960, p.52. 54

Pressing

• Dry Pressing: Simultaneous uniaxial compaction and shaping of power along with binder.

Wide variety of shapes can be formed rapidly and accurately.

• Isostatic pressing: Ceramic powder is loaded into a flexible chamber and pressure is applied outside the chamber with hydraulic fluid.

Examples: Spark plug insulators, carbide tools.

Figure 10.24

Figure 10.25

After J. S. Reed and R. B Runk, “ Ceramic Fabrication Process,” vol 9: “1976, p.74. 55

Extrusion

• Single cross sections and hollow shapes of ceramics can

be produced by extrusion

• Plastic ceramic material is forced through a hard steel or

alloy die by a motor driven auger

• Examples: Refractory brick, sewer pipe, hollow tubes

Figure 10.28

After W. D. Kingery, “ Introduction to Ceramics,” Wiley, 1960. 56

57

Typical Porcelain Composition

(50%) 1. Clay

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

(25%) 3. Fluxing agent (Feldspar)

-- aluminosilicates plus K+, Na+, Ca+

-- upon firing - forms low-melting-temp. glass

58

• Clay is inexpensive

• When water is added to clay -- water molecules fit in between

layered sheets -- reduces degree of van der Waals

bonding -- when external forces applied – clay

particles free to move past one

another – becomes hydroplastic

• Structure of

Kaolinite Clay:

Adapted from Fig. 12.14, Callister &

Rethwisch 8e. (Fig. 12.14 is adapted from

W.E. Hauth, "Crystal Chemistry of

Ceramics", American Ceramic Society

Bulletin, Vol. 30 (4), 1951, p. 140.)

Hydroplasticity of Clay

weak van der Waals bonding

charge neutral

charge neutral

Si 4+

Al 3 +

- OH

O 2-

Shear

Shear

59

• Drying: as water is removed - interparticle spacings decrease

– shrinkage . Adapted from Fig.

13.13, Callister &

Rethwisch 8e. (Fig.

13.13 is from W.D.

Kingery, Introduction

to Ceramics, John

Wiley and Sons, Inc.,

1960.)

Drying and Firing

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

wet body partially dry completely dry

• Firing: -- heat treatment between

900-1400ºC

-- vitrification: liquid glass forms

from clay and flux – flows

between SiO2 particles. (Flux

lowers melting temperature). Adapted from Fig. 13.14, Callister & Rethwisch 8e.

(Fig. 13.14 is courtesy H.G. Brinkies, Swinburne

University of Technology, Hawthorn Campus,

Hawthorn, Victoria, Australia.)

Si02 particle

(quartz)

glass formed around the particle

mic

rog

rap

h o

f p

orc

ela

in

70 mm

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

60

61

Powder Pressing: used for both clay and non-clay compositions.

• Powder (plus binder) compacted by pressure in a mold

-- Uniaxial compression - compacted in single direction

-- Isostatic (hydrostatic) compression - pressure applied by

fluid - powder in rubber envelope

-- Hot pressing - pressure + heat

Ceramic Fabrication Methods (iib)

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION

62

Sintering

Adapted from Fig. 13.16,


Aluminum oxide powder: -- sintered at 1700ºC

for 6 minutes. Adapted from Fig. 13.17, Callister

& Rethwisch 8e. (Fig. 13.17 is from

W.D. Kingery, H.K. Bowen, and

D.R. Uhlmann, Introduction to

Ceramics, 2nd ed., John Wiley and

Sons, Inc., 1976, p. 483.)

15 mm

Sintering occurs during firing of a piece that has

been powder pressed

-- powder particles coalesce and reduction of pore size

Content

Introduction

Glasses

Glass-ceramics

Clay products

Refractories

Abrasives

Cements

Advanced ceramics



Powder pressing

Tape casting

63

64

Tape Casting

• Thin sheets of green ceramic cast as flexible tape

• Used for integrated circuits and capacitors

• Slip = suspended ceramic particles + organic liquid

(contains binders, plasticizers)

Fig. 13.18, Callister &

Rethwisch 8e.

65

• Hardening of a paste – paste formed by mixing cement

material with water

• Formation of rigid structures having varied and complex

shapes

• Hardening process – hydration (complex chemical

reactions involving water and cement particles)

Ceramic Fabrication Methods (iii)

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION

• Portland cement – production of:

-- mix clay and lime-bearing minerals

-- calcine (heat to 1400ºC)

-- grind into fine powder

66

• Categories of ceramics: -- glasses -- clay products

-- refractories -- cements

-- advanced ceramics

• Ceramic Fabrication techniques: -- glass forming (pressing, blowing, fiber drawing).

-- particulate forming (hydroplastic forming, slip casting,

powder pressing, tape casting)

-- cementation

• Heat treating procedures -- glasses—annealing, tempering

-- particulate formed pieces—drying, firing (sintering)

Summary

applications and processing of ceramics - imeng.ndhu.edu.t file4 applications and processing of...

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