Download - Ceramics - Engineering Materials Outline -Engineering Materials Suranaree University of Technology October 2007 • Introduction to ceramics • Structures of ceramics • Processing

CeramicsCeramics-- Engineering MaterialsEngineering Materials

Suranaree University of Technology October 2007

• Introduction to ceramics

• Structures of ceramics

• Processing of ceramics

• General properties and applications of ceramics

• Engineering ceramics, glass and composites

Outline

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ObjectivesObjectives


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• Students are required to understand basic structures,

properties and applications of ceramics as one of the most

important engineering materials.

• Identification and selection of appropriate ceramic

materials for the desirable applications should be made.

• Composite materials are introduced for properties and

applications that cannot be achieved from conventional

materials.

ReferencesReferences


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• Smith, W.F, Hashemi, J., Foundations of material science and

engineering, 4th edition, McGraw-Hill International, ISBN 007-

125690-3.

• Callister Jr., W.D., Fundamentals of materials science and

engineering, 2001, John Wiley&Sons, Inc., ISBN 0-471-39551-X.

• Hull, D., Clyne, T.W., An introduction to composite materials,

2nd edition, 1996, Cambridge University Press, UK, ISBN 0-512-

38855-4.

Introduction to ceramics Introduction to ceramics

and classificationsand classifications


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Chapter 1

What is ceramic?

• Inorganic or non-metallic materials

• Primarily Ionic and covalent bonded

Interesting properties

• Hard and brittle

(depending on type of bonding)

• High melting point (Refractory)

• Wear resistance

• High hot hardness

Grinding wheel

Cemented carbides

Classification of ceramicsClassification of ceramics


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Chapter 1

Ceramics can be divided into various types

Conventional ceramics

Advanced ceramics

• Tableware /sanitary ware/ pottery

• Bricks / tiles

• Glass

• Refractory

• Electrical porcelain

• Bioceramics

• Cutting tools

• Semi-conductor, superconductor

• Ferro-magnetic materials

Bioceramics

Refractory

www.dynacer.com

Ceramic

cutting tools

Simple ceramic crystal structuresSimple ceramic crystal structures


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Chapter 1

Simple ionic arrangement

CN = coordinating number

Radius ratio = rcation/ranion



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Chapter 1

Cesium chloride (CsCl) crystal structure

• Simple ionic bonding (equal numbers of Cs+

and Cl-ions).

• CN = 8, radius ratio = 0.94

• Ex: CsCl, CsBr, TlCl, TlBr, AgMg, LiMg, AlNi

• Similar to BCC in metallic bonding (atomic packing factor = 0.68)



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Chapter 1

Example: Predict the coordinating number for the ionic solids CsCl and NaCl.

Use the following ionic radii for the prediction:

Cs+ = 0.170 nm Na+ = 0.102 nm Cl- = 0.181 nm

The radius ratio for CsCl is 94.0181.0

170.0

)(

)(==

−

+

nm

nm

ClR

Csr

Since this ratio is greater than 0.732, CsCl should

show cubic coordinator (CN = 8)

The radius ratio for NaCl is 56.0181.0

102.0

)(

)(==

−

+

nm

nm

ClR

Nar

Since this ratio is greater than 0.414, but less than

0.732, NaCl should show octahedral coordinator

(CN = 6)



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Chapter 1

Example: Calculate the ionic packing for CsCl. Ionic radii are Cs+ = 0.170 nm

and Cl- = 0.181 nm.

Let r = Cs+ and R = Cl-

nma

nmnma

Rra

405.0

)181.0170.0(23

223

=

+=

+=

CsCl ionic packing factor

68.0

)405.0(

)181.0()170.0(

)1()1(

3

3

343

34

3

3

343

34

=

+=

+=

−+

nmrnmr

a

ionClrionCsr

ππ

ππ



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Chapter 1

Sodium chloride (NaCl) crystal structure

• Highly ionic bonding (equal numbers of Na+

and Cl-ions).

• CN = 6,

• Radius ratio = 0.56

• Ex: MgO, CaO

, NiO, FeO



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Chapter 1

Interstitial sites in FCC and HCP crystal lattice

• Intersitial atoms (small) fit into empty voids/spaces in the lattice.

• Two types of interstitial types : octahedral and tetrahedral

FCC-Octahedral

FCC-Tetrahedral

4 octahedral interstitial

sites/ FCC unit cell

8 tetrahedral interstitial

sites/ FCC unit cell

At type sites

Note: HCP structure is also close-packed-similar to FCC

4

1,4

1,4

1



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Chapter 1

Interstitial sites in FCC crystal lattice



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Chapter 1

Zinc Blend (ZnS) crystal structure

• Equivalent of 4 Zn2+

and 4 S2-

atoms

• CN= 4, (80% covalent character)

• Either Zn or S occupies lattice points

of FCC unit cell while the other occupies

haft the tetrahedral sites.

• Ex: CdS, InAs, InSb, ZnSe.



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Chapter 1

Calcium Fluoride (CaF2) crystal structure

• Consists of 4 Ca2+

and 8 F-atoms

• CN= 4, (80% covalent character)

• Either Ca occupies lattice points of

FCC unit cell while F occupies eight of

the tetrahedral sites.

• Ex: UO2, BaF2, AuAl2.

Note: unoccupied octahedral interstitial UO2 is used as nuclear fuel.



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Chapter 1

Anti fluorite crystal structure

• Consists of anions (O2-

) occupying

4 FCC unit sites and cations (Li+

)

occupying 8 tetrahedral sites.

• Ex: Li2O, Na2O, K2O, Mg2Si.

OLi



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Chapter 1

Corundum (Al2O3) crystal structure

• O locating at the lattice sites

of hexagonal close-packed

unit cell.

• Al occupying 2/3 of

octahedral sites to balance

electrical neutrality � give

some distortion

Note: There are only 2 Al 3+ for 3 O 2-



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Chapter 1

Spinel (MgAl2O4) crystal structure

• Typical for oxides (AB2O4).

• Oxygen ions form an FCC lattice

• A= metal ion (2+) and B= metal ion

(3+) occupying tetrahedral and

octahedral sites, depending of particular

type of spinel.

• Normally used for non-metallic

magnetic materials, electronic

applications.

O red, Al blue, Mg yellow;

tetrahedral and octahedral coordination

som.web.cmu.edu/structures/S060-MgAl2O4_web.jpg



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Chapter 1

Perovskite (CaTiO3) crystal structure

• Ca2+ (corners) and O2- (face centre) form and FCC lattice

• Ti4+ locating at octahedral sites at the centre of the unit cell.

• Typical for piezoelectric materials.

• Ex: SrTiO3, CaZrO3, SrZrO3, LaAlO3



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Chapter 1

Carbon and its allotropes

• Graphite

�Carbon atoms form layers of strongly

covalent bonded hexagonal array and

weak secondary bonded across layers.

�Anisotropic property- good thermal and

electrical conductivity on the basal plane.

�Density 2.26 g/cm3.



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Chapter 1


• Diamond

� Cubic structure (covalent bond)

�Isotropic

� Density 3.51 g/cm3

�High thermal conductivity but

very low electrical conductivity

(insulator)



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Chapter 1


• Buckminster Fullerene (Bucky ball)

�Made up of 12 pentagons and 20 hexagons (look like football)

� Contain 60 carbons covalently bonded, therefore C60.

�Possible applications in electronics industries, fuel cells, lubricants and

superconductors.



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Chapter 1


• Carbon nanotube

•Hexagonal patterns on the tube

and pentagonal on the end cap.

• 20x stronger than steels (45 GPa).

• Can form ropes, fibres and thin

films

• Applications: chemical sensors,

fibre materials for composites,

electron producing cathode.



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Chapter 1

Silicate structures

• Mainly consist of silicon and oxygen.

• Ex, glass, clay, feldspar, micas.

• Cheap, abundant on earth’s crust.

• Important for engineering construction materials.

Basic structure

• Strong bonding of Silicate (SiO44-) tetrahedron

• 50% covalent 50% ionic



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Chapter 1

Silicate structures Island, chain and ring structures of silicates

• Strong bonding of silicate (SiO44-)

tetrahedron

• 50% covalent 50% ionic

• Each oxygen has one electron

available � can bond with other

positive ions.

• Ex: (Mg, Fe)2SiO4.

• Forming chains (MgSiO3)

• Forming rings (SiO32-)

(Be3Al2(SiO3)2)



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Chapter 1

Silicate structures Sheet structure of silicates

• Three corners are bonded together with other three.

• Unit formula (Si2O52-)

• Can form kaolinite.

• Ex: Talc.

5242

2

42

2

52 )()( OSiOHAlOHAlOSi →+ +−



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Chapter 1

Silicate structures Silicate networks

• Silica (SiO2 network)

• All four corners of SiO44- share

oxygen atoms.

• Three basic silica structures,

quartz, tridymite and crystobalite

High quartz tridymite crystoballite

867oC 1470oC

Silica liquidLow quartz

1710oC573oC

www.dreamtime.bz/quartz Quartz



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Chapter 1

Silicate structures Silicate networks

• Feldspar

Potassium feldspar

geology.about.com

• Industrially important

• Three dimensional silicate network

• Al3+ replaces some of Si4+ and the

charge is balanced by Na+, K+, Ca2+ ,

Ba2+ at the interstitial sites.

232

2322

2322

6..

6..

6..

SiOOAlCaO

SiOOAlONa

SiOOAlOK



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Chapter 1

Silicate mineral composition

Processing of ceramicsProcessing of ceramics


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Chapter 1

Forming

• Pressing

• Isostatic pressing

• Extrusion

• Casting

Ceramic particles are normally mixed with binders or

lubricants in the dry, plastic or liquid to form into shapes.

Thermal treatments

• Drying

• Sintering

• Vitrification



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Chapter 1

Pressing • Ceramic particulates can be pressed in the dry, plastic

or wet condition in the die to form shaped products.

Dry pressing• Refractory

• Rapid, uniform and good tolerance

• Ex: alumina, titanate, ferrite

Filling

Pressing

Ejection



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Chapter 1

Isostatic pressing

• Powder is placed within a deformable container

and subjected to hydrostatic pressure.

• Simultaneous densification, low porosity.

• Near net shape process �100% material

utilization.

• High operating cost.

Hot isostatic pressing (HIP).

/www.sintec-keramik.com



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Chapter 1

Hot Isostatic Pressing (HIP)• Components are loaded

into furnace, which is placed

into pressure vessel.

• Temperature and pressure

are raised simultaneously

and held.

• Cooling is carried out as

the gas is released.

• Components are removed

from the furnace.



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Chapter 1

Cold Isostatic Pressing

• Powder is sealed in a flexible

mould (or ‘bag’), of for example

polyurethane and then subjected

to a uniform hydrostatic

pressure.

• Ex: refractories, bricks, spark

plug insulator, carbide tools,

crucible, bearings

CIP graphite blocks



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Chapter 1

Example of isostatic pressing of spark plug insulator

Mould

a) Pressed blank

b) Turned insulator

c) Fired insulator

d) Glazed and decorated



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Chapter 1

Slip casting

Main steps

1. Slip preparation

2. Slip casting

3. Draining

4. Trimming, removing

and finishing

• Forming thin-wall complex

shapes of uniform thickness.

• Can be done in vacuum.



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Chapter 1

Extrusion • Plastic state forming under high pressure

• Producing refractory bricks, sewer pipes, hallow tiles,

technical ceramics, electrical insulators.



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Chapter 1

Thermal treatments

• Drying

• Sintering

• Vitrification

Important state in making ceramics stronger

Drying • To remove water (and organic

binders) before firing

• Improving green strength

• Carried out at 100-300oC.

www.ceramic-drying.co.uk



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Chapter 1

Sintering Small particles are bonded together by solid state diffusion

Porous Denser, more coherentT < Tm

• Atomic diffusion takes place

at the area of contact to form

necking

• Particles get larger and

material is denser with

sintering time.

• Providing equilibrium grains.

• Lowered surface energy

Ex: Alumina, beryllia, ferrite and titanates



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Chapter 1

Example of MgO sintering at 1430oC in air at various times

Sintering temp Porosity


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Chapter 1

Vitrification

Ex: Porcelain, structural clay products, electronic components


• The glass phase liquifies and fill the pores in the material.

• Then solidifies to form a vitreous matrix that bonds the

unmelted materials upon cooling.

Download - Ceramics - Engineering Materials Outline -Engineering Materials Suranaree University of Technology October 2007 • Introduction to ceramics • Structures of ceramics • Processing

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