3. Sintering: The Definition
It is the thermal treatment of a powder or compact, at a
temperature below the melting point of the main constituent, for
the purpose of increasing its strength by the metallurgical
bonding of its particles.
4. Sintering is basically removal of pores between particles
accompanied by shrinkage (densification) and grain growth.
5. • Solid-state sintering (SSS): Only solid phase is present in sintering temperature.
• Liquid phase sintering (LPS) : Small amounts of liquid are found during sintering
i.e. < 20% liquid.
• Reactive Sintering : Particles react with each other to form new product phases.
Types of sintering
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9. Driving force -- Reduction of surface area .
-- Lowering of surface
energy.
10. • Particle size:
Materials transport over smaller
distances, higher surface energies.
Larger grains grow at the expense of
smaller ones. Coarsening of the
grains.
Factors influencing sintering
• Particle packing:
Improves the number of contact points
between particles. Relative density
increased. Faster densification, less
volume shrinkage.
• Particle shape:
Irregular shaped particles with higher
surface area/volume ratio, have a
higher driving force for sintering.
Particles that pack poorly sinter poorly
11. Stages of Sintering
(a, b) Initial stage sintering: Formation of strong bonds
and necks between particles at the contact points.
Moderate decrease of porosity (initial 40-50%) from
particle rearrangement.
(c)Intermediate stage sintering: The size of the necks
increases and the amount of porosity decreases. The
sample shrinks (the centers of the grains move towards
each other. The grains transforms from spheres to
truncated octahedra (tetrakaidecahedra). This stage
continues until pores are closed (r.d. 90%).
(d)Final stage sintering: Pores are slowly eliminated
and major grain growth can occur.
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13. In hot-pressing and hot isostatic pressing an additional driving force is provided by the external stress/ pressure.
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17. Advantages of Sintering
o Allows making complex geometries- shaping of materials which have a
very high melting point.
o Reduction of porosity.
o Increase conductivity.
o Preservation of purity.
o Good mechanical characteristics.
o Cost economy compared with other processes.
18. Dis-advantages of Sintering
o High initial capital cost
o Size is limited based on the size of the chamber sintering machine.
o High temperature of the process leads to high energy cost.
o Large quantity of material is required.
19. Conclusion
Sintering is a critical phase in the production of ceramic bodies. By
controlling the density and microstructure formation, sintering now
emerged as a processing technology of ceramic materials.
Tailoring the structural, mechanical, electrical, magnetic and optical
properties is widens the application of ceramics in various fields.
