Advanced ceramics
Advanced ceramics are used in high technological areas and are made from specially
prepared raw materials using chemical processing techniques in a rigorously controlled
environment.
They exhibit high degree of industrial efficiency, through their carefully designed
microstructures (Si3N4) and dimensional precision.
Advanced ceramics are further classified into (i) structural and (ii) functional ceramics.
Structural ceramics are used in structures and machines such as steam, gas turbines, electric
motors and generators. They are subjected to thermal or thermo-mechanical load.
Functional ceramics are used in transistors, ceramic magnets, laser, piezoelectric cells.
Silicon nitride Ceramic laser Transistor Spark plug
source
Large elongated crystals in Si3N4 helps in crack deflection and fracture toughness improvement. 1
Difference between traditional and
advanced ceramics
Attributes Traditional ceramic Advanced ceramic Iso-static pressing
Raw material Natural raw material Artificial synthesized.
e.g. Clay, silica e.g. Si3N4, SiC
Forming Potters wheel Rubber pressing
Sintering Fire Kiln, Ascending Hot-isostatic pressing, Hot
Kiln pressing,
Products Pottery, Brick Engineering components
Structure Optical microscope Electron microscope
Potters wheel Roman fire kiln Advanced ceramic components
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Difference between traditional and
advanced ceramics
Synthesis of
raw materials –
Powders
Advanced Traditional
ceramics ceramics
Consolidation
NDT – Non destructive testing; XRD – X-ray diffraction 3
Classification of ceramics by
chemical composition
Ceramics can also be classified based
Corundum – Al2O3 on the composition.
Mullite – 3 Al2O3. 2SiO2; 2Al2O3. SiO2
Cristobalite – SiO2 (Tetragonal) Depending upon the constituents,
Tridymite – SiO2 (orthorhombic) ceramics can be binary, ternary or
Quartz – SiO2 (Trigonal or hexagonal) quaternary compounds.
Cordierite – 2 MgO. 2Al2O3. 5SiO2
Ytrrium iron garnet – A3B2Si3O12 Ceramics can be again classified based
Apatite – Ca5P3O12F on its properties and application such as
electro-ceramics, magnetic ceramics,
Akermanite – Ca2MgSi2O7
opto-ceramics, bio ceramics and
Anorthite – CaAl2Si2O8 structural ceramics.
Phenacite – Ba2SiO4
Perovskite – CaTiO3 Carbides – SiC, WC, TiC, TaC, ZrC, B4C
Nitrides – Si3N4, BN, TiN, ZrN, AlN
Spinel – AB2O4
Oxynitrides – SiAlON
Zircon – ZrSiO4 Borides – TiB2, YB2, ZrB12
A – Element or chemical species with oxidation state 2+ ; B – Element with oxidation state 3+
Example of spinel - MgAl2O4 4
Oxide ceramics
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Raw materials for ceramic processing
Production cost-breakup
Process step Cost
Raw materials 5-10
Powder preparation 15-20
Shaping 5-10
Consolidation 15-20
Finishing 15-20
Inspection, rejection 30-45
Raw material cost is low, since
most of the constituents of
advanced ceramics are
abundantly available.
However, difficult to process, fabricate or shape advanced ceramics.
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Processing of ceramics-
Stage – 1 - Shaping
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Processing of ceramics
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Processing of ceramics
Ceramics may be shaped or processed by
(i) Die pressing
(ii) Isostatic pressing (rubber pressing / hydrostatic pressing)
(iii) Slip casting
(iv) Injection molding,
(v) Tape casting – E.g. Doctor blade
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Die pressing
Uniaxial pressure applied to the powder placed in a die, between two rigid punches.
Die pressing is a simple method, easily applied, however, difficult to apply uniform pressure
on the particles of the ceramic body, being molded.
Die pressing is conducted at room temperature (cold pressing) or high temperatures (hot-
pressing. The pressure varies between 10,000 psi to 120,000 psi (69 MPa to 830 MPa).
Note: Hot pressing of silicon carbide is carried out at temperature about 2000ºC. 10
Isostatic pressing
Isostatic pressing increases the no of contact points between the particles,
facilitating the compaction process. In addition, this method minimizes frictional
resistance with the wall surfaces.
Advantages
• Produces body in complex shapes.
• Reduces variation in physical properties.
Isostatic pressing involves applying
pressure from multiple directions through a
liquid or gaseous medium surrounding the
compacted part.
In hot-isostatic pressing, gas
A flexible (commonly polyurethane) mold (nitrogen or argon) is used.
immersed in a pressurized liquid medium
(commonly water) is used to transmit the It combines pressing and sintering,
force in cold-isostatic pressing. causing consolidation of powder
particles, healing voids and pores.
The work pressures are commonly between 15,000 psi to 44,000 psi 11
