This document provides an introduction to ceramics and their classification. It discusses that ceramics are inorganic compounds composed of metallic and non-metallic elements bonded ionically or covalently. Ceramics can be classified by their application, structure, or composition. Common structures include crystalline structures like rock salt and zinc blend. Ceramic properties include hardness, high melting temperatures, and electrical/thermal insulation. Due to these properties, ceramics find applications in areas like aerospace, automotive, electronics and more. The document also discusses ceramic crystal structures, imperfections, and phase diagrams.

1. Introduction about ceramics and
bioceramics
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2. Part I: Introduction about ceramics
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3. Introduction
 Ceramics: generally ceramics are inorganic compounds,
composed of more than one element formed from metallic
(Al, Mg, Na, Ti, W, Si, B) and non-metallic (O, N, C) elements.
• For example, alumina (Al2O3) is a ceramic made up of
aluminum atoms and oxygen atoms.
• Bonds are partially or totally ionic or the combination of ionic
and covalent bonding.
• Ceramics are typically characterized as possessing a high
melting temperature (i.e., “refractory”), hard and brittle,
electrical and thermal insulators.
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4. Classification of ceramics
o 1. Functional Classification (application and products):
• Glasses • Clay products
• Refractories • Abrasives
• Cements • Advanced ceramics
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5.  Glasses products: based on SiO2
• Applications: containers and optical glasses, etc .
 Traditional ceramics: most made up of clay, silica and feldspar
(product like clay brick, glasses and tile, portland cement,
refractories, etc).
 Advanced ceramics: typically consist of pure or nearly pure
compounds such as aluminum oxide, silicon carbide, silicon
nitride and zirconium oxide etc.
• Advanced ceramics exhibits superior mechanical, electrical,
optical, and magnetic properties and corrosion or oxidation
resistance. Applications: heat engines, cutting tools, die
materials, sensors, laser, bearing, superconductors etc.
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7. o 2. Structural Classification: - Crystalline ceramics & Non-
Crystalline ceramics.
• (i) Crystalline ceramics: Single-phase or multi-phase
ceramics.
• (ii) Non-crystalline ceramics: Natural and synthetic inorganic
glasses.
• (iii) "Glass-bonded" ceramics: Fire clay products-crystalline
phases are held in glassy matrix.
• (iv) Cements: Crystalline and non-Crystalline
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8. o 3. Classification based on composition:
• Oxides • Carbides • Nitrides • Sulfides • Fluorides, etc
 Examples:
• Oxide Ceramics: dominant crystalline phase, Al2O3, BaTiO3, etc
• Non-oxide Ceramics: carbon, SiC, BN, TiB2, sialon
• Glass-ceramics: partially crystallized glass SiO2-Li2O
• Silicate Ceramics: presence of glassy phase in a porous
structure
clay ceramics (with mullite – 3Al2O3 + 2SiO2)
silica ceramics (with cordierite 2MgO + 2Al2O3+. 2SiO)
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9. Properties of ceramics
• The properties of ceramic materials, like all materials, are
dictated by the types of atoms present, the types of bonding
between the atoms, and the way the atoms are packed
together.
• The bonding of atoms together is much stronger in covalent
and ionic bonding (of ceramics) than in metallic. That is why,
generally speaking, metals are ductile and ceramics are
brittle.
• Due to ceramic materials wide range of properties, they are
used for a multitude of applications.
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10.  In general, advanced ceramics have the following inherent
properties:
• Hard and wear resistant
• Resistant to high temperatures
• Good corrosion resistance
• Low thermal conductivity
• Low electrical conductivity
• Brittle (Resistant to plastic deformation)
• Chemically inert
• Non magnetic
• Low tensile and fracture strength
 However, some ceramics exhibit high thermal conductivity
and/or high electrical conductivity.
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11. Applications of ceramics
 Ceramics offer many advantages compared to other
materials: They are harder and stiffer than steel; more heat
and corrosion resistant than metals or polymers; less dense
than most metals and their alloys; and their raw materials are
both plentiful and inexpensive.
 Ceramic materials display a wide range of properties which
facilitate their use in many different product areas.
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12.  Advanced ceramics has excellent properties of high strength,
high temperature, wear resistance, corrosion resistance, high
insulation, which metal, plastic and other materials don't
possess, and has been widely used in electronic, electrical,
mechanical, aerospace, chemicals, textiles and many other
fields.
• Aerospace: space shuttle tiles, thermal barriers, high
temperature glass windows, fuel cells
• Used as cutting tool
• Used in military –ceramic armour, structural components for
ground, air and naval vehicles, missiles, sensors
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13. • Automotive: catalytic converters, ceramic filters, airbag
sensors, spark plugs, pressure sensors, vibration sensors,
oxygen sensors, safety glass windshields, piston rings
• Computers: insulators, resistors, superconductors, capacitors,
ferroelectric components, microelectronic packaging
• Consumer Uses: glassware, windows, pottery, magnets,
dinnerware, ceramic tiles, lenses, home electronics,
microwave transducers
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14. Ceramic crystal structure
• It is a unique arrangement of atoms or molecules in a
crystalline liquid or solid. Since ceramics are composed of two
or more elements, their crystal structures tend to be more
complex than those of metals.
• Ceramic crystal structure is determined by the relative charge
and relative size of the anion and cation. Remember that in a
ceramic, the cation gives up electrons to the anion, so the
anion is normally much larger.
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15.  Crystal structure is defined by:
 1. Magnitude of the electrical charge on each ion.
• Crystal must be electrically neutral (total cation, anion charges must be
equal). Chemical formula of a compound indicates the ratio of cations to
anions, or composition that achieves this charge balance,
• E.g. in CaF2: 2 F – ions (negative ions) and 1 Ca2+ ion (positive ions).
 2. Relative size of the cation and anion.
• The ratio of the atomic radii (rcation/ranion) dictates the atomic
arrangement. Stable structures have cation/anion contact.
• (i.e. Crystal structure of the ceramic is determined by the coordination
number)
• Stable ceramic crystal structures: anions surrounding a cation are all in
contact with that cation otherwise unstable. For a specific coordination
number there is a critical or minimum cation anion radius ratio rC/rA for
which this contact can be maintained.
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16. • The metallic ions, or cations, are smaller and positively charged since they
give up their valence electrons to the non-metallic, negatively charged
ions, or anions. Usually compounds between metallic ions (e.g. Fe, Ni, Al)
– called cations and non-metallic ions (e.g. O, N, Cl) - called anions. Cations
(positive electric charge (e.g. Na+)) usually smaller than anions (negative
electric charge (e.g. Cl-). Each tries to maximize number of opposite
neighbours.
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17. Co ordination number
• The Coordination Number (CN): is defined as the number of
anions that can fit around a cation.
• This number increases as the radius ratio increases.
• The number of anions that can „fit‟ around a cation is related
to the relative size difference between the ions, and this size
difference can be described using the radius ratio.
• When this number is small, then only a few anions can fit
around a cation. When this number is large, then more anions
can fit around a cation.
• When CN is 4, it is known as tetrahedral coordination; when it is 6, it is
octahedral; and when it is 8, it is known as cubic coordination.
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18.  Radius ratio:
• Radius ratio is the ratio of the ionic radius of the cation to the
ionic radius of the anion in a cation anion compound. This is
simply given by
• The radius ratio when the anions just start to contact each
other and the central cation is critical (limiting/minimum)
radius ratio.
• As the size of a cation increases, more anions of a particular
size can pack around it.
• This ratio can be determined by simple geometrical analysis.
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20. Ceramics structures types:
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21. AX-Type Crystal Structure
 Most common ceramics are made of equal number of cations
and anions, and are referred to as AX compounds (A-cation,
and X-anion).
 These ceramics assume many different structures, named
after a common material that possesses the particular
structure. Examples for AX ceramics structure
• Rock Salt Structure -NaCl, MgO, MnS, LiF, FeO
• Cesium Chloride Structure (CsCl)
• Zinc Blende Structure (ZnS, ZnTe, SiC).
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22. • 1. AX-Rock Salt Structure: The rock salt structure is like two
superimposed FCC structures. Eg) NaCl
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24. Imperfections in material
• The periodic nature of crystalline materials can be interrupted
by imperfections. Imperfections in ceramic crystals include
point defects and impurities like in metals.
• It is important to have knowledge about the types of
imperfections that exist and the roles they play in affecting
the behavior of materials.
 Types of Imperfections:
• Vacancy atoms
• Interstitial atoms Point defects
• Substitutional atoms
• Dislocations Line defects.
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25. Point Defects in Ceramics
 Point defects include the Frenkel and Schottky defects. Frenkel or
Schottky defects: no change in cation to anion ratio →compound is
stoichiometric.
• Vacancies: vacancies exist in ceramics for both cations and anions
• Interstitials: interstitials exist for cations (interstitials are not
normally observed for anions because anions are large relative to the
interstitial sites)
 Frenkel defect: a cation vacancy and a cation interstitial or an
anion vacancy and anion interstitial. A Frenkel-defect occurs when a
host atom moves into a nearby interstitial position to create a
vacancy-interstitial pair of cations.
 Schottky defect: pair of anion and cation vacancies. Schottky
defect occurs when a host atom leaves its position and moves to
the surface creating a vacancy-vacancy pair.
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27. Impurities in Ceramics
• Impurities are atoms which are different from the host.
• Impurity atoms can exist as either substitutional or interstitial
solid solutions.
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28. Phase diagram of ceramics
• Phase diagrams map the number and types of phases that are
present, the composition of each phase, and the
microstructures that exist.
• The phase diagram is important in understanding the
formation and control of the microstructure of poly phase
ceramics.
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29. Phase diagram of Al2O3 – Cr2O3
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30. Phase diagram of MgO - Al2O3
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31. Mechanisms of plastic deformation of
ceramic materials
• In materials science, deformation is a change in the shape or
size of an object due to an applied force or a change in
temperature.
• At room temperature most ceramic materials suffer fracture
before the onset of plastic deformation.
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32. Deformation of Crystalline ceramics
 For crystalline ceramics, plastic deformation occurs, by the
motion of dislocations (slip), which is difficult due to the
structure and the strong local (electrostatic) potentials. There
is very little plastic deformation before fracture. One reason
for the hardness and brittleness of these materials is the
difficulty of slip (dislocation motion). This is not a problem in
metals, since all atoms are electrically neutral.
 Ceramics in which the bonding is highly covalent, slip is difficult and they
are brittle for the following reasons:
• (1) the covalent bonds are relatively strong;
• (2) there are also limited numbers of slip systems; and
• (3) dislocation structures are complex.
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33. Deformation of non-crystalline ceramics
 Non-crystalline ceramics, (common glass) deform by viscous
flow (like very high-density liquids). Viscosity decreases
strongly with increases temperature.
 Plastic deformation does not occur by dislocation motion for
noncrystalline ceramics because there is no regular atomic
structure. Rather, these materials deform by viscous flow, the
same manner in which liquids deform; the rate of
deformation is proportional to the applied stress.
 In response to an applied shear stress, atoms or ions slide
past one another by the breaking and reforming of inter-
atomic bonds. However, there is no prescribed manner or
direction in which this occurs, as with dislocations. Viscous
flow on a macroscopic scale is demonstrated in Figure.
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34. • The characteristic property for viscous flow, viscosity, is a
measure of a noncrystalline material‟s resistance to
deformation. For viscous flow in a liquid that originates from
shear stresses imposed by two flat and parallel plates, the
viscosity is the ratio of the applied shear stress and the
change in velocity dv with distance dy in a direction
perpendicular to and away from the plates.
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35. Mechanical properties of ceramics
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 Some mechanical properties of ceramics materials make its
application wide in engineering field.
 Mechanical Properties
• 1. Ceramics posses great hardness and resistance to wear and
can be used for grinding.
• 2. Ceramics posses good compressive strength.
• 3. Ceramic materials have low tensile strength.
• 4. They generally fail due to stress concentration on cracks,
pores etc.
• 5. Most ceramics posses low fracture strength and fail in a
brittle manner.
• 6. Values of Modulus of Elasticity for ceramics ranges from
*** N/m2 to ****N/m2 .

36.  This strong bonding also accounts for the less attractive
properties of ceramics, such as low ductility and low tensile
strength. The absence of free electrons is responsible for
making most ceramics poor conductors of electricity and heat.
• Ceramics are brittle.
• The compressive strength is typically ten times the tensile
strength. This makes ceramics good structural materials under
compression (e.g., bricks in houses, stone blocks in the
pyramids).
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37. Ceramic Brittle Fracture Surfaces
 Intergranular (between grains)
 Intragranular (within grains)
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38.  Characteristic Fracture behavior in ceramics
• – Origin point
• – Initial region (mirror) is flat and smooth
• – After reaches critical velocity crack branches
mist
hackle
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39. Ceramics processing methods
• The very specific character of ceramics high temperature
stability and high hardness makes conventional fabrication
routes unsuitable for ceramic processing.
• Ceramic processes involve forming, firing and finishing. Most
other ceramic products are manufactured through powder
metallurgy processing. Powder is added with water and/or
additives such as binders, followed by a shape forming
process. Other forming methods for ceramics processing
include extrusion, slip casting, pressing, tape casting and
injection molding.
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40. • Extrusion – viscous mixture of ceramic particles, binder and
other additives is fed through an extruder where continuous
shape of green ceramic is produced. Then the product is dried
and sintered.
• Injection molding –Mixture of ceramic powder, plasticizer,
thermoplastic polymer, and additives is injected into die with
use of an extruder. Then polymer is burnt off, before sintering
rest of the ceramic shape. It is suitable for producing complex
shapes. Extrusion and Injection molding are used to make
ceramic tubes, bricks, and tiles
• Powder metallurgy process
• Slip casting
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41. References
• Ceramics, Module 4 (part one). Department of Mechanical Engineering
SSET.
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42. • Thanks
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