This document provides information on the properties of ceramics. It begins with an introduction to ceramics, including their atomic bonding and crystal structures. It then discusses defects in ceramics and general properties such as brittleness, toughness, and strength at high temperatures. The document classifies ceramics and discusses properties and applications of various types, including electronic ceramics like piezoelectric and dielectric ceramics. Processing methods are also briefly mentioned.

3.  Thermal properties of ceramics
 Mechanical properties of ceramics
 Electrical properties of ceramics
Outline
 Introduction
 Atomic bonding in ceramics
 Ceramics crystal structure
 Defects in ceramics
 General properties of ceramics
 Classification of ceramics
 Electronic ceramics
 Processing of ceramics

4.  The word ‘ceramic’ is originated from Greek word
“keromikos”, which means ‘burnt stuff’.
 Ceramics are compounds of metallic and non-metallic
elements.
Introduction
 Are wide-ranging group of materials whose
ingredients are clays, sand and feldspar.
 Are Inorganic non-metallic materials obtained by
the action of heat and subsequent cooling.

5.  Always composed of more than one element (e.g., Al2O3,
NaCl, SiC, SiO2)
 Bonds are partially or totally ionic, and can have
combination of ionic and covalent bonding
 Generally hard and brittle
 Generally electrical and thermal insulators
 Can be optically opaque, semi-transparent, or Transparent

6. • 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).

7. 7
Atomic Bonding in Ceramics
 Bonding:
 Degree of ionic character may be large or small:
SiC: small
CaF2: large
 Can be ionic and/or covalent in character.
 % ionic character increases with difference
in electronegativity of atoms.

8. Ceramic Crystal Structures
 Crystal structure is defined by -Magnitude of
the electrical charge on each ion.
Oxide structures
– oxygen anions larger than metal cations
– close packed oxygen in a lattice (usually FCC)
– cations fit into interstitial sites among oxygen ions

9.  Stable ceramic crystal structures: anions surrounding a
cation are all in contact with that cation.
 For a specific coordination number there is a critical or
minimum cation anion radius ratio rC/rA for which this
contact can be maintained.

10. Two interpenetrating FCC lattices
NaCl, MgO, LiF, FeO have this crystal structure
Rock Salt Structure Cesium Chloride Structure
Examples of crystal structures in ceramics

11. Zinc Blende Structure: typical for
compounds where covalent
bonding dominates. C.N. = 4
ZnS, ZnTe, SiC have this crystal structure
Fluorite (CaF2):
FCC structure with 3 atoms per
lattice point

12. Silicate Ceramics
• Most common elements on earth are Si & O
• SiO2 (silica) polymorphic forms are quartz, crystobalite, &
tridymite
• The strong Si-O bonds lead to a high melting temperature
(17100C) for this material
12
Si4+
O2-
Adapted from Figs.
12.9-10, Callister &
Rethwisch 8e
crystobalite

13. 13
Defects in Ceramics
• Vacancies
-- vacancies exist in ceramics for both cations and
anions
• Interstitials
Adapted from Fig. 12.20, Callister &
Rethwisch 8e. (Fig. 12.20 is from
W.G. Moffatt, G.W. Pearsall, and J.
Wulff, The Structure and Properties
of Materials, Vol. 1, Structure, John
Wiley and Sons, Inc., p. 78.)
Cation
Interstitial
Cation
Vacancy
Anion
Vacancy
 interstitials exist for cations
 interstitials are not normally observed for anions
because anions are large relative to the interstitial sites

14. 14
Point Defects in Ceramics
 Point defects in ionic crystals are charged.
 The Coulombic forces are very large and any charge
imbalance has a strong tendency to balance itself. To
maintain charge neutrality several point defects can
be created:
Shottky Defect
 a paired set of cation and anion vacancies.
Shottky
Defect:
Frenkel
Defect
Frenkel Defect
 a cation vacancy-cation interstitial pair.

15.  Low ductility
– Very brittle
– High elastic modulus
 Low toughness
– Low fracture toughness
– Indicates the ability of a crack or flaw to
produce a catastrophic failure
 Low density
– Porosity affects properties
 High strength at elevated temperatures
General Properties of ceramics

16. Thermal properties
1)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

17.  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)
2)Thermal conductivity

18.  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 )
 The thermal stresses responsible for the response to
temperature stress depend on:
-geometrical boundary conditions
-thermal boundary conditions
-physical parameters (modulus of elasticity, strength…)
3)Thermal shock resistance

19. STRESS-STRAIN BEHAVIOR of selected materials
Al2O3
thermoplastic
http://www.keramvaerband.de/brevier_engl/5/5_2.htm
Mechanical Properties of Ceramics

20. 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.
http://www.keramverband.de/brevier_engl/5/3/4/5_3_4.htm

21. 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 >
 Some typical hardness values for ceramic materials
are provided below:
 The high hardness of technical ceramics results in favourable
wear resistance.
 Ceramics are thus good for tribological applications.
http://www.dynacer.com/hardness.htm
Hardness

22. http://www.subtech.com/dokuwiki/doku.php?id=fracture_toughness
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Toughness
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

23.  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
http://www.keramverband.de/brevier_engl/5/3/5_3_2.htm
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Porosity

24. 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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25. 25
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).
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26.  Ceramics are classified in many ways. It is due to
divergence in composition, properties and applications.
 Based on their composition, ceramics are:
1.Classification –Ceramics
 Carbides
 Nitrides
 Sulfides
 Fluorides
etc.
CERAMICS
Oxides
Nonoxides
Composite

27. 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

28. • 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)

29. • Ceramic-Based Composites:
 Tough
 low and high oxidation
resistance (type related)
 variable thermal and electrical
conductivity
 complex manufacturing processes
 high cost.
Ceramic Matrix Composite (CMC) rotor

30. Based on their engineering applications ,ceramics
are classified in to two groups as: traditional and
advanced ceramics.
 Traditional ceramics–most made up of clay,
silica and feldspar
 Advanced ceramics–these consist of highly
purified aluminum oxide(Al2O3), silicon carbide
(SiC) and silicon nitiride (Si3N4)
2.Classification –Ceramics

31. Classification of ceramics

33.  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
Traditional Ceramics

34. 1) Clay Ceramics
 Made from natural clays and mixtures of clays and added
crystalline ceramics.
 These include:
Whitewares
 Crockery
 Floor and wall tiles
 Sanitary-ware
 Electrical porcelain
 Decorative ceramics
 Whitewares
 Structural Clay Products
Whiteware: Bathrooms

35. 2)Refractories
 Firebricks for furnaces and ovens.
 Have high Silicon or Aluminium oxide content.

36. 3)Amorphous Ceramics (Glasses)
 Main ingredient is Silica (SiO2)
 If cooled very slowly will form crystalline structure.
 If cooled more quickly will form amorphous structure
consisting of disordered and linked chains of Silicon
and Oxygen atoms.
 This accounts for its transparency as it is the crystal
boundaries that scatter the light, causing reflection.
 Glass can be tempered to increase its toughness and
resistance to cracking.

37. Three common types of glass:
 Soda-lime glass - 95% of all glass, windows
containers etc.
 Lead glass - contains lead oxide to improve
refractive index
 Borosilicate - contains Boron oxide, known as
Pyrex.
Glass Containers

38. 4)Abrasives
 Natural (garnet, diamond, etc.)
 Synthetic abrasives (silicon carbide, diamond,
fused alumina, etc.) are used
 for grinding
 for cutting Si wafers
 polishing
 for oil drilling
lapping, or pressure
blasting of materials.
Two Kyocera ceramic knives (Y:ZrO2)
oil drill bits

39. 5) Cements
 Used to produce concrete roads, bridges, buildings,
dams.

40.  have been developed over the past half century.
 Include artificial raw materials, exhibit specialized
properties, require more sophisticated processing
 Advanced ceramics are also referred to as “special,”
“technical,” or “engineering” ceramics.
 They exhibit superior mechanical properties,
corrosion/oxidation resistance, or electrical, optical, and/or
magnetic properties.
Advanced Ceramics

41.  laser host materials
 piezoelectric ceramics
 ceramics for dynamic random access
memories (DRAMs), often produced in small
quantities with higher prices.
 as thermal barrier coatings to protect metal
structures, wearing surfaces
 Engine applications :Si3N4, SiC, Zirconia
(ZrO2), Alumina (Al2O3))
 Advanced ceramics include newer materials
such as

42. Engine Components
Rotor (Alumina)
Gears (Alumina)

43. Turbocharger
Ceramic Rotor

44. Ceramic Si3N4 bearing parts
Radial rotor made from Si3N4 for a gas
turbine engine
The Porsche Car
silicon carbide disk brake
Structural ceramics

45. Silicon Carbide
 Automotive Components
in Silicon Carbide
 Chosen for its heat and
wear resistance
 Body armour and other
components chosen for their
ballistic properties.

46. Ceramics in the field Biomaterials

47. Metallic framework
Angry gums
Ceramic
framework
Why ceramics ?
Dental implant

48. The first use of ceramics in the electrical industry
took advantage of their stability when exposed to
extremes of weather and to their high electrical
resistivity, a feature of many siliceous materials.
 Ceramics with higher resistivities also had high
negative temperature coefficients of resistivity,
contrasting with the very much lower and positive
temperature coefficients characteristic of metals.
Electronic Ceramics

49. Electronic Ceramics
Ferroelectric
Pyroelectric
Piezoelectric
Dielectric
Dielectric Property
Piezoelectricity
Pyroelectricity
Ferroelectricity

50. Piezoelectricity
 Mechanical and electrical energy conversion phenomena,
discovered by France Scientist Pierre and Jacques Curie
brother in 1880.
 They showed that crystals of tourmaline, quartz, topaz,
cane sugar, and Rochelle salt generate electrical
polarization from mechanical stress.
 Piezoelectric Material will generate electric potential
when subjected to some kind of mechanical stress.

51. Crystal Structure of piezoelectric ceramics
 A traditional piezoelectric ceramic is a mass of perovskite
crystals.
 Pervoskite structure,
 Each crystal consists of a small tetravalent metal ion,
usually titanium or zirconium, in a lattice of larger divalent
metal ions, usually lead or barium, and O2- ions
with the chemical formula as ABO3
e.g. : BaTiO3, , CaTiO 3

52. Above the Curie point each perovskite
crystal in the fired ceramic element exhibits
a simple cubic symmetry
At temperatures below the Curie point,
however, each crystal has tetragonal or
rhombohedral symmetry and a dipole
moment.

53. Applications of piezoelectric ceramics
Piezoelectric ceramics used as the resonator and filter in
communication system with frequency lower than 100MHz。
The ceramic filter and resonator are made of high stability
piezoelectric ceramics that functions as a mechanical resonator.
 The frequency is primary adjusted by the size and thickness of
the ceramic element.
 Typical application includes telephones, remote controls and
radios.

54. Processing of ceramics
powder compact or
“green”
ceramic
Forming
Sintering or
densification or
firing
T 2Tm/3

55. Ceramic powder processing route: synthesis of
powder , followed by fabrication of green product
which is then consolidated to obtain the final
product.
Synthesis of powder involves
1)Ceramic powder processing
 crushing,
 grinding
 Separating impurities
 blending different powders.

56.  Grinding refers to the reduction of small pieces
after crushing to fine powder
 Accomplished by abrasion, impact, and/or
compaction by hard media such as balls or rolls
 Examples of grinding include:
 Ball mill
 Roller mill
 Impact grinding
Ball mill Roller mill
Grinding

57. Green component can be manufactured in
different ways:
Green component is then fired/sintered to get
final product.
 tape casting
 slip casting
 extrusion
 injection molding and
 cold-/hot-compaction.
Shaping Processes

58. Slip casting
• A suspension of ceramic powders in water , slip, is
poured into a porous plaster mold .
• Water from the mix is absorbed into the plaster to form a
firm layer of clay at the mold surface

59. http://global.kyocera.com/fcworld/first/process06.html
 Raw materials are mixed with resin to provide the necessary
fluidity degree.
 Then injected into the molding die
 The mold is then cooled to harden the binder and produce a
"green" compact part (also known as an unsintered powder
compact).

60. Drying process
• Water must be removed from clay piece before
firing
• Shrinkage is a problem during drying. Because
water contributes volume to the piece, and the
volume is reduced when it is removed.
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• Sintering step is still very much required
• Driving force for sintering–reduction in total surface area
and thus energy.
• Functions of sintering are the same as before:
1. Bond individual grains into a solid mass
2. Increase density
3. Reduce or eliminate porosity
Sintering of Ceramics

61. Finishing Operations for Ceramics
• Parts made of ceramics sometimes require finishing,
with one or more of the following purposes:
1. Increase dimensional accuracy
2. Improve surface finish
3. Make minor changes in part geometry
• Finishing usually involves abrasive processes
– Diamond abrasives must be used to cut the
hardened ceramic materials

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