Ceramics - Engineering Materials Outline

T. Udomphol Ceramics- Engineering Materials

Outline

• Introduction to ceramics
• Structures of ceramics
• Processing of ceramics
• General properties and applications of ceramics
• Engineering ceramics, glass and composites

Suranaree University of Technology October 2007

Objectives

T. Udomphol • 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.

Suranaree University of Technology October 2007

T. Udomphol References

• 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.

Suranaree University of Technology October 2007

Chapter 1

Introduction to ceramics
and classifications

Grinding wheel

What is ceramic?

• Inorganic or non-metallic materials
• Primarily Ionic and covalent bonded

T. Udomphol Interesting properties

• Hard and brittle Cemented carbides
(depending on type of bonding)
October 2007
• High melting point (Refractory)
• Wear resistance
• High hot hardness

Suranaree University of Technology

Chapter 1

Classification of ceramics

Ceramics can be divided into various types

T. Udomphol Conventional ceramics www.dynacer.com Refractory

• Tableware /sanitary ware/ pottery Bioceramics October 2007
• Bricks / tiles
• Glass
• Refractory
• Electrical porcelain

Advanced ceramics

• Bioceramics Ceramic
• Cutting tools cutting tools
• Semi-conductor, superconductor
• Ferro-magnetic materials

Suranaree University of Technology

Chapter 1

Simple ceramic crystal structures

Simple ionic arrangement

T. Udomphol

CN = coordinating number October 2007
Radius ratio = rcation/ranion

Suranaree University of Technology

T. Udomphol Chapter 1

Simple ceramic crystal structures

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)

Suranaree University of Technology October 2007

Chapter 1

Simple ceramic crystal structures

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

T. Udomphol The radius ratio for CsCl is r(Cs+ ) = 0.170 nm = 0.94
R(Cl − ) 0.181 nm

Since this ratio is greater than 0.732, CsCl should
show cubic coordinator (CN = 8)

The radius ratio for NaCl is r(Na+ ) = 0.102 nm = 0.56
R(Cl − ) 0.181 nm

Since this ratio is greater than 0.414, but less than
0.732, NaCl should show octahedral coordinator
(CN = 6)

Suranaree University of Technology October 2007

Chapter 1

Simple ceramic crystal structures

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- 3a = 2r + 2R
3a = 2(0.170 nm + 0.181 nm)
T. Udomphol a = 0.405 nm

CsCl ionic packing factor

4 πr 3 (1 Cs+ion) + 4 πr 3 (1 Cl −ion)
3 3
=
a3

4 πr 3 (0.170nm) + 4 πr 3 (0.181nm)
3 3
=
(0.405)3

= 0.68

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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

Suranaree University of Technology October 2007

Chapter 1

Simple ceramic crystal structures

T. Udomphol 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

4 octahedral interstitial
sites/ FCC unit cell

FCC-Tetrahedral

8 tetrahedral interstitial

sites/ FCC unit cell

At  1 , 1 , 1  type sites
4 4 4

Note: HCP structure is also close-packed-similar to FCC October 2007

Suranaree University of Technology

Chapter 1

Simple ceramic crystal structures

Interstitial sites in FCC crystal lattice

T. Udomphol

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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.

Li O

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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- October 2007

Suranaree University of Technology

Chapter 1

Simple ceramic crystal structures

Spinel (MgAl2O4) crystal structure O red, Al blue, Mg yellow;
tetrahedral and octahedral coordination

T. Udomphol • 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.

Suranaree University of Technology som.web.cmu.edu/structures/S060-MgAl2O4_web.jpg
October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

Carbon and its allotropes

• Diamond
Cubic structure (covalent bond)
Isotropic
Density 3.51 g/cm3
High thermal conductivity but

very low electrical conductivity
(insulator)

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

Carbon and its allotropes
• 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.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

Carbon and its allotropes

• 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.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

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

Suranaree University of Technology October 2007

Chapter 1

Simple ceramic crystal structures

T. Udomphol 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)

Suranaree University of Technology October 2007

Chapter 1

Simple ceramic crystal structures

Silicate structures Sheet structure of silicates

• Three corners are bonded together with other three.

• Unit formula (Si2O52-)

• Can form kaolinite. Si O2− + Al (OH ) 2+ → Al (OH ) 4 Si O
25 2 4 2 25
T. Udomphol
• Ex: Talc.

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

Silicate structures Silicate networks
• Silica (SiO2 network)

• All four corners of SiO44- share
oxygen atoms.
• Three basic silica structures,
quartz, tridymite and crystobalite

www.dreamtime.bz/quartz Quartz

573oC 867oC 1470oC 1710oC

Low quartz High quartz tridymite crystoballite Silica liquid

Suranaree University of Technology October 2007

T. Udomphol Chapter 1

Simple ceramic crystal structures

Silicate structures Silicate networks
• Feldspar
• 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.

K 2O.Al2O3 .6 SiO
2

Na2O.Al2O3.6SiO2

geology.about.com CaO.Al2O3.6SiO2

Potassium feldspar October 2007

Suranaree University of Technology

Chapter 1

Simple ceramic crystal structures

Silicate mineral composition

T. Udomphol

Suranaree University of Technology October 2007

Chapter 1

Processing of ceramics

Ceramic particles are normally mixed with binders or
lubricants in the dry, plastic or liquid to form into shapes.

Forming Thermal treatments

T. Udomphol • Pressing • Drying
• Isostatic pressing • Sintering
• Extrusion • Vitrification
• Casting

Suranaree University of Technology October 2007

Chapter 1

Processing of ceramics

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
T. Udomphol • Ex: alumina, titanate, ferrite

Filling October 2007
Pressing
Ejection

Suranaree University of Technology

Chapter 1

Processing of ceramics

Isostatic pressing /www.sintec-keramik.com

T. Udomphol • 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.

Suranaree University of Technology Hot isostatic pressing (HIP).

October 2007

Chapter 1

Processing of ceramics

Hot Isostatic Pressing (HIP)

T. Udomphol • 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.

Suranaree University of Technology October 2007

Chapter 1

Processing of ceramics

T. Udomphol 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

Suranaree University of Technology CIP graphite blocks

October 2007

Chapter 1

Processing of ceramics

Example of isostatic pressing of spark plug insulator

T. Udomphol Mould

a) Pressed blank October 2007
b) Turned insulator
c) Fired insulator
d) Glazed and decorated

Suranaree University of Technology

T. Udomphol Processing of ceramics Chapter 1

Slip casting October 2007

• Forming thin-wall complex
shapes of uniform thickness.
• Can be done in vacuum.

Main steps

1. Slip preparation
2. Slip casting
3. Draining
4. Trimming, removing

and finishing

Suranaree University of Technology

Chapter 1

Processing of ceramics

Extrusion • Plastic state forming under high pressure
• Producing refractory bricks, sewer pipes, hallow tiles,
technical ceramics, electrical insulators.

T. Udomphol

Suranaree University of Technology October 2007

Chapter 1

Processing of ceramics

Thermal treatments Important state in making ceramics stronger

• Drying Drying • To remove water (and organic
• Sintering binders) before firing
T. Udomphol • Vitrification
• Improving green strength

• Carried out at 100-300oC.

www.ceramic-drying.co.uk October 2007
Suranaree University of Technology

Chapter 1

Processing of ceramics

Sintering Small particles are bonded together by solid state diffusion

Porous T < Tm Denser, more coherent

T. Udomphol • 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 October 2007

Suranaree University of Technology

Chapter 1

Processing of ceramics

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

T. Udomphol

Sintering temp Porosity

Suranaree University of Technology October 2007

Chapter 1

Processing of ceramics

Vitrification • 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.

T. Udomphol

Ex: Porcelain, structural clay products, electronic components

Suranaree University of Technology October 2007