CERAMICS

1. CERAMICS

2. SPECTRUM OF CERAMICS USES

3. WHAT ARE CERAMICS?
• Periodic table with ceramics compounds indicated by a
combination of one or more metallic elements (in light
color) with one or more nonmetallic elements (in dark
color).

4. WHAT ARE CERAMICS?
• To be most frequently silicates, oxides, nitrides and
carbides
• Typically insulative to the passage of electricity and
heat
• More resistant to high temperatures and harsh
environments than metals and polymers
• Hard but very brittle

5. CERAMIC CRYSTAL STRUCTURES
• ceramics that are predominantly ionic in nature
have crystal structures comprised of charged ions,
where positively-charged (metal) ions are called
cations, and negatively-charged (non-metal) ions
are called anions – the crystal structure for a given
ceramic depends upon two characteristics:

6. CERAMIC CRYSTAL STRUCTURES
1. the magnitude of electrical charge on each
component ion, recognizing that the overall structure
must be electrically neutral
2. the relative size of the cation(s) and anion(s),which
determines the type of interstitial site(s) for the
cation(s) in an anion lattice

7. Radius ratio rules
• The crystal must be electrically neutral.
• Sizes or radii of cations and anions
• rc/ra is less than unity
• Each cations prefer to have as many nearest neighbor
anions as possible .
• The coordination number is related to the cation-
anion radius ratio.

9. The size of ion depends on
1. Coordination number
• Ionic radius tends to increase as the number of
nearest neighbor ions of opposite charge increases
2. Charges of ions
• When an electron is removed from an atom or ion ,
the remaining valence electrons become more tightly
to the nucleus, which results in decrease in ionic
radius

10. EXAMPLE OF CRYSTAL STRUCTURE
Rock salt structure(AX)(NaCl ) Fluorite structure(AX2)(CaF2)
Perovskite structure(ABX3)(BaTiO3) Spinel structure(AB2X4)(MgAl2O4)
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11. AX- type crystal structures
Rock salt structure(AX)(NaCl )
• Coordination number is 6 for
both ions
• These structure is generated fro
FCC arrangement of anions each
one cation situated at the cube
center and one at the center of
the 12 cube edges.
• Equivalent crystal structure from
FCC arrangement of cations.
• MgO, MnS, LiF, FeO

12. Zinc blende (Sphalerite ) structure
• Coordination number is 4
• All ions are tetrahedrally
coordinated.
• All corner and face positions
occupied by S atoms while
Zn atoms fill interior
tetrahedral positions
• ZnTe, SiC

13. Cesium chloride structure
• Coordination number is 8 for
both ions
• The anions are located at the
corners of cube and anions at
center of cube

14. AMXP- type crystal structures
• rc/ra for CaF2 is 0.8 ,
coordination number is 8
• Ca ions are positioned at
the center of the cube and F
ions at the corners.
• Similar crystal structure to
CsCl, but only half the
center cube position is
occupied by Ca+2 ions.
• One unit cell consists of 8
cubes.
• ZrO2, UO2,PuO2, ThO2
Fluorite structure(AX2)(CaF2)

15. AMBNXP- type crystal structures
BaTiO3 (Perovskite ) crystal structure
• More than one type of
cations

17. IMPERFECTIONS IN CERAMICS
• Include point defects and impurities
• Non-stoichiometry refers to a change in composition
• the effect of non-stoichiometry is a redistribution of
the atomic charges to minimize the energy
• Charge neutral defects include the Frenkel defects(a
vacancy- interstitial pair of cations) and Schottky
defects (a pair of nearby cation and anion vacancies)
• Defects will appear if the charge of the impurities is
not balanced
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19. Al2O3-Cr2O3 Phase diagram

20. MgO-Al2O3 Phase diagram

21. PROPERTIES OF CERAMICS
• Extreme hardness
– High wear resistance
– Extreme hardness can reduce wear caused by
friction
• Corrosion resistance
• Heat resistance
– Low electrical conductivity
– Low thermal conductivity
– Low thermal expansion
– Poor thermal shock resistance
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22. GENERAL COMPARISON OF MATERIALS
Property Ceramic Metal Polymer
Hardness Very High Low Very Low
Elastic modulus Very High High Low
Thermal expansion High Low Very Low
Wear resistance High Low Low
Corrosion resistance High Low Low
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23. GENERAL COMPARISON OF MATERIALS
Property Ceramic Metal Polymer
Ductility Low High High
Density Low High Very Low
Electrical conductivity Depends High Low
on material
Thermal conductivity Depends High Low
on material
Magnetic Depends High Very Low
on material
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24. CLASSIFICATION OF CERAMICS
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25. CLASSIFICATION OF CERAMICS
• Traditional Ceramics
 the older and more generally known types
(porcelain, brick, earthenware, etc.)
 Based primarily on natural raw materials
of clay and silicates
 Applications;
building materials (brick, clay pipe, glass)
household goods (pottery, cooking ware)
manufacturing ( abbrasives, electrical
devices, fibers)
Traditional Ceramics
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26. CLASSIFICATIONS OF CERAMICS
• Advanced Ceramics
 have been developed over the past half
century
 Include artificial raw materials, exhibit
specialized properties, require more
sophisticated processing
 Applied as thermal barrier coatings to
protect metal structures, wearing
surfaces,
 Engine applications (silicon nitride (Si3N4),
silicon carbide (SiC), Zirconia (ZrO2),
Alumina (Al2O3))
bioceramic implants
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27. CLASSIFICATION OF CERAMICS
• Oxides: Alumina, zirconia
• Non-oxides: Carbides, borides, nitrides, silicides
• Composites: Particulate reinforced, combinations of oxides and
non-oxides
CERAMICS
Oxides
Nonoxides
Composite
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28. CLASSIFICATION OF CERAMICS
• Oxide Ceramics:
 Oxidation resistant
 chemically inert
 electrically insulating
 generally low thermal conductivity
 slightly complex manufacturing
 low cost for alumina
 more complex manufacturing
higher cost for zirconia.
zirconia
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29. CLASSIFICATION OF CERAMICS
• Non-Oxide Ceramics:
 Low oxidation resistance
 extreme hardness
 chemically inert
 high thermal conductivity
 electrically conducting
 difficult energy dependent
manufacturing and high cost.
Silicon carbide cermic foam filter (CFS)
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30. CLASSIFICATION OF CERAMICS
• Ceramic-Based Composites:
 Toughness
 low and high oxidation resistance
(type related)
 variable thermal and electrical
conductivity
 complex manufacturing processes
 high cost.
Ceramic Matrix Composite (CMC) rotor
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31. CLASSIFICATION OF CERAMICS
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32. CLASSIFICATIONS OF CERAMICS
• Amorphous
 the atoms exhibit only short-range
order
 no distinct melting temperature (Tm)
for these materials as there is with
the crystalline materials
 Na20, Ca0, K2O, etc Amorphous silicon and thin film PV cells
CERAMICS
amorphous
crystalline
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33. CLASSIFICATIONS OF CERAMICS
• Crystalline
 atoms (or ions) are arranged in a
regularly repeating pattern in three
dimensions (i.e., they have long-
range order)
 Crystalline ceramics are the
“Engineering” ceramics
– High melting points
– Strong
– Hard
– Brittle
– Good corrosion resistance
a ceramic (crystalline) and a glass (non-crystalline)
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34. THERMAL PROPERTIES
• most important thermal properties of ceramic materials:
 Heat capacity : amount of heat required to raise material temperature by
one unit (ceramics > metals)
 Thermal expansion coefficient: the ratio that a material expands in
accordance with changes in temperature
 Thermal conductivity : the property of a material that indicates its ability
to conduct heat
 Thermal shock resistance: the name given to cracking as a result of rapid
temperature change
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35. THERMAL PROPERTIES
 Thermal expansion
• The coefficients of thermal
expansion depend on the bond
strength between the atoms that
make up the materials.
• Strong bonding (diamond,
silicon carbide, silicon nitrite) →
low thermal expansion
coefficient
• Weak bonding ( stainless steel)
→ higher thermal expansion
coefficient in comparison with
fine ceramics
Comparison of thermal expansion coefficient
between metals and fine ceramics
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36. THERMAL PROPERTIES
 Thermal conductivity
• generally less than that of metals such as steel or copper
• ceramic materials, in contrast, are used for thermal insulation due to their low
thermal conductivity (except silicon carbide, aluminium nitride)
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37. THERMAL PROPERTIES
 Thermal shock resistance
• A large number of ceramic materials are sensitive to thermal shock
• Some ceramic materials → very high resistance to thermal shock is despite of low
ductility (e.g. fused silica, Aluminium titanate )
• Result of rapid cooling → tensile stress (thermal stress)→cracks and consequent failure
• The thermal stresses responsible for the response to temperature stress depend on:
-geometrical boundary conditions
-thermal boundary conditions
-physical parameters (modulus of elasticity, strength…)
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38. MECHANICAL PROPERTIES OF CERAMICS
STRESS-STRAIN BEHAVIUR of selected materials
Al2O3
thermoplastic
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39. MECHANICAL PROPERTIES OF CERAMICS
Flexural Strength
The stress at fracture using
this flexure test is known as
the flexural strength.
Flexure test :which a rod
specimen having either a
circular or rectangular cross
section is bent until fracture
using a three- or four-point
loading technique
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40. For a rectangular cross section, the flexural strength σfs is equal to,
L is the distance between support points
When the cross section is circular,
R is the specimen radius
Stress is computed from,
• specimen thickness
•the bending moment
•the moment of inertia of the cross section
MECHANICAL PROPERTIES OF CERAMICS
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41. MECHANICAL PROPERTIES OF CERAMICS
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42. MECHANICAL PROPERTIES OF CERAMICS
Hardness
Hardness implies a high
resistance to deformation and is
associated with a large modulus of
elasticity.
In metals, ceramics and most
polymers, the deformation
considered is plastic deformation of
the surface. For elastomers and
some polymers, hardness is defined
at the resistance to elastic
deformation of the surface.
Technical ceramic
components are therefore
characterised by their stiffness
and dimensional stability.
Hardness is affected from
porosity in the surface, the grain
size of the microstructure and the
effects of grain boundary phases.
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43. Material Class Vickers Hardness (HV) GPa
Glasses 5 – 10
Zirconias, Aluminium Nitrides 10 - 14
Aluminas, Silicon Nitrides 15 - 20
Silicon Carbides, Boron
Carbides
20 - 30
Cubic Boron Nitride CBN 40 - 50
Diamond 60 – 70 >
Test procedures for determining the hardness according to Vickers, Knoop
and Rockwell.
Some typical hardness values for ceramic materials are provided below:
MECHANICAL PROPERTIES OF CERAMICS
The high hardness of technical ceramics results in favourable wear resistance.
Ceramics are thus good for tribological applications.
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44. MECHANICAL PROPERTIES OF CERAMICS
Elastic modulus
The elastic modulus E [GPa] of almost
all oxide and non-oxide ceramics is
consistently higher than that of steel.
This results in an elastic deformation of
only about 50 to 70 % of what is found
in steel components.
The high stiffness implies, however, that
forces experienced by bonded
ceramic/metal constructions must
primarily be taken up by the ceramic
material.
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45. MECHANICAL PROPERTIES OF CERAMICS
Density
The density, ρ (g/cm³) of
technical ceramics lies
between 20 and 70% of the
density of steel.
The relative density, d [%],
has a significant effect on
the properties of the
ceramic.
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46. MECHANICAL PROPERTIES OF CERAMICS
A comparison of typical mechanical characteristics of some ceramics with grey
cast-iron and construction steel
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47. MECHANICAL PROPERTIES OF CERAMICS
Porosity
Technical ceramic materials have
no open porosity.
Porosity can be generated through
the appropriate selection of raw
materials, the manufacturing
process, and in some cases through
the use of additives.
This allows closed and open pores
to be created with sizes from a few
nm up to a few µm.
http://www.ucl.ac.uk/cmr/webpages/spotlight/articles/colombo.htm
Change in elastic modulus with the amount of
porosity in SiOC ceramic foams obtained from a
preceramic polymer
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48. MECHANICAL PROPERTIES OF CERAMICS
Strength
The figure for the strength of
ceramic materials, [MPa] is
statistically distributed depending
on
•the material composition
•the grain size of the initial
material and the additives
•the production conditions
•the manufacturing process
Strength distribution within batches
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49. MECHANICAL PROPERTIES OF CERAMICS
Toughness
Ability of material to resist
fracture
affected from,
•temperature
•strain rate
•relationship between the strenght
and ductility of the material and
presence of stress concentration
(notch) on the specimen surface
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50. MECHANICAL PROPERTIES OF CERAMICS
Material KIc (MPa-m1 / 2)
Metals
Aluminum alloy (7075) 24
Steel alloy (4340) 50
Titanium alloy 44-66
Aluminum 14-28
Ceramics
Aluminum oxide 3-5
Silicon carbide 3-5
Soda-lime-glass 0.7-0.8
Concrete 0.2-1.4
Polymers
Polystyrene 0.7-1.1
Composites
Mullite fiber reinforced-
mullite composite
1.8-3.3
Some typical values of
fracture toughness for
various materials
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51. ELECTRICAL PROPERTIES OF CERAMIC
• Electrical conductivity of ceramics varies with
The Frequency of field applied effect
• charge transport mechanisms are frequency
dependent.
The temperature effect
• The activation energy needed for charge migration is
achieved through thermal energy and immobile
charge career becomes mobile.
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52. ELECTRICAL PROPERTIES OF CERAMIC
• Most of ceramic materials are dielectric.
(materials, having very low electric
conductivity, but supporting electrostatic
field).
• Dielectric ceramics are used for
manufacturing capacitors, insulators and
resistors.
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53. SUPERCONDUCTING PROPERTIES
• Despite of very low electrical conductivity of most of the ceramic materials,
there are ceramics, possessing superconductivity properties (near-to-zero
electric resistivity).
• Lanthanum (yttrium)-barium-copper oxide ceramic may be superconducting at
temperature as high as 138 K. This critical temperature is much higher, than
superconductivity critical temperature of other superconductors (up to 30 K).
• The critical temperature is also higher than boiling point of liquid Nitrogen
(77.4 K), which is very important for practical application of superconducting
ceramics, since liquid nitrogen is relatively low cost material.
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54. Applications: Advanced Ceramics
Heat Engines
• Advantages:
– Run at higher temperature
– Excellent wear & corrosion
resistance
– Low frictional losses
– Ability to operate without a
cooling system
– Low density
• Disadvantages:
– Brittle
– Too easy to have voids-
weaken the engine
– Difficult to machine
• Possible parts – engine block, piston coatings, jet engines
Ex: Si3N4, SiC, & ZrO2

55. Applications: Advanced Ceramics
• Ceramic Armor
– Al2O3, B4C, SiC & TiB2
– Extremely hard materials
• shatter the incoming projectile
• energy absorbent material underneath

56. Applications: Advanced Ceramics
Electronic Packaging
• Chosen to securely hold microelectronics & provide heat
transfer
• Must match the thermal expansion coefficient of the
microelectronic chip & the electronic packaging material.
Additional requirements include:
– good heat transfer coefficient
– poor electrical conductivity
• Materials currently used include:
• Boron nitride (BN)
• Silicon Carbide (SiC)
• Aluminum nitride (AlN)
– thermal conductivity 10x that for Alumina
– good expansion match with Si

57. Thank You 