Ceramics- Engineering Materials
T. Udomphol
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
T. Udomphol
Objectives
• 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
References
T. Udomphol
• Smith, W.F, Hashemi, J., Foundations of material science and
engineering, 4th edition, McGraw-Hill International, ISBN 007125690-3.
• 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 0-51238855-4.
Suranaree University of Technology
October 2007
Chapter 1
Introduction to ceramics
and classifications
Grinding wheel
What is ceramic?
T. Udomphol
• 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
Cemented carbides
Suranaree University of Technology
October 2007
Chapter 1
Classification of ceramics
Ceramics can be divided into various types
T. Udomphol
Conventional ceramics
• Tableware /sanitary ware/ pottery
• Bricks / tiles
• Glass
• Refractory
• Electrical porcelain
www.dynacer.com
Refractory
Bioceramics
Advanced ceramics
• Bioceramics
• Cutting tools
• Semi-conductor, superconductor
• Ferro-magnetic materials
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Ceramic
cutting tools
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
Simple ionic arrangement
CN = coordinating number
Radius ratio = rcation/ranion
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Cesium chloride (CsCl) crystal structure
+
• Simple ionic bonding (equal numbers of Cs and Cl ions).
T. Udomphol
• 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
T. Udomphol
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
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:
and R =
3a = 2r + 2 R
Cl-
T. Udomphol
Let r =
Cs+
Calculate the ionic packing for CsCl. Ionic radii are Cs+ = 0.170 nm
and Cl- = 0.181 nm.
3a = 2(0.170 nm + 0.181 nm)
a = 0.405 nm
CsCl ionic packing factor
=
4
3
πr 3 (1 Cs + ion) + 43 πr 3 (1 Cl −ion)
a3
3
3
4
4
π
r
nm
π
r
(
0
.
170
)
(0.181nm)
+
3
= 3
(0.405) 3
= 0.68
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Sodium chloride (NaCl) crystal structure
+
• Highly ionic bonding (equal numbers of Na and Cl ions).
T. Udomphol
• CN = 6,
• Radius ratio = 0.56
• Ex: MgO, CaO
, NiO, FeO
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Interstitial sites in FCC and HCP crystal lattice
• Intersitial atoms (small) fit into empty voids/spaces in the lattice.
T. Udomphol
• 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  14 , 14 , 14  type sites
Note: HCP structure is also close-packed-similar to FCC
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
Interstitial sites in FCC crystal lattice
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Zinc Blend (ZnS) crystal structure
2+
T. Udomphol
• Equivalent of 4 Zn
2-
and 4 S 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
Chapter 1
Simple ceramic crystal structures
Calcium Fluoride (CaF2) crystal structure
2+
T. Udomphol
• Consists of 4 Ca
-
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
Chapter 1
Simple ceramic crystal structures
Anti fluorite crystal structure
T. Udomphol
2-
• Consists of anions (O ) occupying
+
4 FCC unit sites and cations (Li )
occupying 8 tetrahedral sites.
• Ex: Li2O, Na2O, K2O, Mg2Si.
Li
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O
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
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 2Suranaree University of Technology
October 2007
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.
som.web.cmu.edu/structures/S060-MgAl2O4_web.jpg
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Perovskite (CaTiO3) crystal structure
• Ca2+ (corners) and O2- (face centre) form and FCC lattice
T. Udomphol
• 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
Chapter 1
Simple ceramic crystal structures
Carbon and its allotropes
T. Udomphol
• 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
Chapter 1
Simple ceramic crystal structures
Carbon and its allotropes
T. Udomphol
• 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
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)
T. Udomphol
Contain 60 carbons covalently bonded, therefore C60.
Possible applications in electronics industries, fuel cells, lubricants and
superconductors.
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
Carbon and its allotropes
T. Udomphol
• 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
Chapter 1
Simple ceramic crystal structures
T. Udomphol
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
Silicate structures
Island, chain and ring structures of silicates
T. Udomphol
• 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
T. Udomphol
Silicate structures
Sheet structure of silicates
• Three corners are bonded together with other three.
• Unit formula (Si2O52-)
• Can form kaolinite. Si2O52− + Al2 (OH ) 24+ → Al2 (OH ) 4 Si2O5
• Ex: Talc.
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
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
867oC
573oC
Low quartz
High quartz
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1470oC
tridymite
1710oC
crystoballite
Silica liquid
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
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 SiO2
Na2O. Al2O3 .6 SiO2
geology.about.com
CaO. Al2O3 .6 SiO2
Potassium feldspar
Suranaree University of Technology
October 2007
Chapter 1
Simple ceramic crystal structures
T. Udomphol
Silicate mineral composition
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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.
T. Udomphol
Forming
Thermal treatments
• 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.
T. Udomphol
Dry pressing
• Refractory
• Rapid, uniform and good tolerance
• Ex: alumina, titanate, ferrite
Filling
Pressing
Ejection
Suranaree University of Technology
October 2007
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.
Hot isostatic pressing (HIP).
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
Hot Isostatic Pressing (HIP)
• Components are loaded
into furnace, which is placed
into pressure vessel.
T. Udomphol
• 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
CIP graphite blocks
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
T. Udomphol
Example of isostatic pressing of spark plug insulator
Mould
a)
b)
c)
d)
Pressed blank
Turned insulator
Fired insulator
Glazed and decorated
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
Slip casting
T. Udomphol
• Forming thin-wall complex
shapes of uniform thickness.
• Can be done in vacuum.
Main steps
1.
2.
3.
4.
Slip preparation
Slip casting
Draining
Trimming, removing
and finishing
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
• Plastic state forming under high pressure
• Producing refractory bricks, sewer pipes, hallow tiles,
technical ceramics, electrical insulators.
T. Udomphol
Extrusion
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
T. Udomphol
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
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
Sintering Small particles are bonded together by solid state diffusion
T. Udomphol
Porous
T < Tm
Denser, more coherent
• 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
Suranaree University of Technology
October 2007
Chapter 1
Processing of ceramics
T. Udomphol
Example of MgO sintering at 1430oC in air at various times
Sintering temp
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Porosity
October 2007
Chapter 1
Processing of ceramics
T. Udomphol
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.
Ex: Porcelain, structural clay products, electronic components
Suranaree University of Technology
October 2007