Ceramics are compounds made by heating and cooling metallic and non-metallic elements. There are traditional ceramics like bricks and tiles as well as industrial/engineering ceramics used in things like semiconductors and turbines. Ceramics have stronger bonds than metals and better hardness, thermal, and electrical resistance. Common ceramic materials include clay, flint, feldspar, and porcelain. Alumina, zirconia, carbides, nitrides, glass, and graphite are important types of ceramics used for their properties like strength, corrosion resistance, and conductivity.

1. CERAMICS
Definition:
 A compound of metallic and non-metallic elements prepared by the action of heat
and subsequent cooling.
 There are two general categories of ceramic;
 Traditional ceramics – tiles, brick, sewer pipe, pottery
 Industrial ceramics (engineering, high-tech, or fine ceramics) – turbine,
semiconductors, cutting tools
 The structure of ceramics is maybe crystalline or partly crystalline structure, or may
be amorphous.
 Generally atoms in ceramics are covalent or ionic bonded and the much stronger is
metallic bonds.
 The hardness and thermal and electrical resistance in ceramics are better than in
metals.
 The grain size influences the structure of ceramics (finer grain size has give higher
strength and toughness).
 The oldest materials to make ceramics is clay (fine-grained sheet like structure) i.e.
kaolinite (a white clay of silicate of aluminum with alternating weakly bonded layers
of silicon and aluminum ions).
 The other common materials are flint (a rock composed of very fine grained SiO₂)
and feldspar (a group of crystalline minerals of aluminum silicate and potassium,
calcium or sodium).
 Porcelain is a white ceramic made of kaolin, quartz, and feldspar used mostly in
kitchen appliance and bath ware.

2. Mechanical properties


3. Physical properties
 Most ceramics have low specific gravity.
 They also have very high melting or decomposition temperatures.
 The thermal conductivity of ceramics decrease with increasing
temperature and porosity because air is a poor thermal conductor.
 k = kₒ(1 – P)
 kₒ = thermal conductivity at zero porosity
 P = the porosity as a fraction of the total volume
 Thermal shock or thermal fatigue may be caused by internal
stresses formed during thermal expansion and thermal conductivity.
 Thermal cracking or spalling (a small piece or layer from the surface
break off) will not occur when combine with lower thermal
expansion and high thermal conductivity.
 Anisotropy of thermal expansion • that varies with different
direction which lead to cracking.

4. Alumina
 Also called corundum or emery
 Most widely used
 Used in pure form or as raw material
 High hardness and moderate strength
 Alumina + other oxides are used as refractory
materials for high-temp applications
 Suitable as electrical and thermal insulation,
cutting tools/abrasives, etc.

5. Zirconia
 Good toughness, good resistance to thermal
shock, wear and corrosion
 Have low friction coefficient
 Used in hot extrusion die, grinding
beads/dispersion media for aerospace coatings,
etc.
 Have thermal stability and low thermal
conductivity

6. Carbides
 Made of tungsten and titanium,silicon
 Examples : Tungsten carbide (WC),
titanum carbide (TiC), silicon carbide (SiC)

7. Nitrides
 Cubic boron nitride (CBN)
 Titanum nitride (TiN)
 Silicon nitride (Si3N4)

8. Glass
 Amorphous solid
 Super-cooled liquid (cooled at a rate too high for
crystal formation)
 Content •more than 50% silica (glass former)
 Types of commercial glasses •¨ sodalime glass
(most common), lead alkali glass, borosilicate
glass, aluminosilicate glass, 96% silica glass, fused
silica glass
 Thermal classification - hard (greater heat, e.g.,
borosilicate) or soft glass (e.g., soda lime glass •¨
lampworking)

9. Mechanical properties Physical properties
 Perfectly elastic and  Low coefficient of
brittle thermal expansion
 Bulk form has strength  High electrical resistivity
+/- 140MPa  Dielectric strength
 Strength measurement  CTE lower than metals
→ bending and plastic, may
 Static fatigue (same approach zero
with ceramics)

10. Glass ceramics
 High crystalline microstructure
 Stronger than glass
 Shaped and then heat treated
 Treatment •process known as
devitrification(recrystallization of glass)
 Near •zero coefficient of thermal
expansion, high thermal shock resistance

11. Graphite
 Crystalline form of carbon •layered
structure
 Basal planes or sheets of close packed C
atoms
 Weak when sheared along the layers
 Also known as lampblack •(pigment
 High electrical and thermal conductivity
 Good resistance to thermal shock and
high temperature

12. Types of graphite
 Fibers •- important use in reinforced plastics and
composite materials
 Foams - high service temperature, chemical
inertness, low coefficient of thermal expansion
and electrical properties
 Carbon foams - graphitic or non-graphitic
structures
 Buckyballs - carbon molecules in the shape of
soccer balls. Also called
fullerents, chemicallyinert, and act like solid
lubricant particles

13. Diamond
 Diamond-Like Carbon (DLC) •developed as
diamond film coating
 Can be coated with Ni, Cu, or Ti for improved
performance
 Cutting tools materials (single or polycrystalline)
 Abrasive in grinding
 Dressing of grinding wheels (abrasive sharpening)
 Dies for wire drawing
 Cutting tools and dies coating