Ceramics - Engineering Materials Outline -Engineering Materials Suranaree University of Technology...
Transcript of Ceramics - Engineering Materials Outline -Engineering Materials Suranaree University of Technology...
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
T.
Udom
phol
ObjectivesObjectives
Suranaree University of Technology October 2007
T.
Udom
phol
• 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
Suranaree University of Technology October 2007
T.
Udom
phol
• 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
Suranaree University of Technology October 2007
T.
Udom
phol
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
Suranaree University of Technology October 2007
T.
Udom
phol
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
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Simple ionic arrangement
CN = coordinating number
Radius ratio = rcation/ranion
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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)
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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)
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Interstitial sites in FCC crystal lattice
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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.
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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.
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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-
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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.
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Carbon and its allotropes
• Diamond
� Cubic structure (covalent bond)
�Isotropic
� Density 3.51 g/cm3
�High thermal conductivity but
very low electrical conductivity
(insulator)
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
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.
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
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.
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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)
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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 →+ +−
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
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
Simple ceramic crystal structuresSimple ceramic crystal structures
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Silicate mineral composition
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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.
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Example of isostatic pressing of spark plug insulator
Mould
a) Pressed blank
b) Turned insulator
c) Fired insulator
d) Glazed and decorated
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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.
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Extrusion • Plastic state forming under high pressure
• Producing refractory bricks, sewer pipes, hallow tiles,
technical ceramics, electrical insulators.
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
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
Processing of ceramicsProcessing of ceramics
Suranaree University of Technology October 2007
T.
Udom
phol
Chapter 1
Example of MgO sintering at 1430oC in air at various times
Sintering temp Porosity
Processing of ceramicsProcessing of ceramics
T.
Udom
phol
Chapter 1
Vitrification
Ex: Porcelain, structural clay products, electronic components
Suranaree University of Technology October 2007
• 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.