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