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Ceramics and glasses

Which statement about sintering of ceramic powders is correct?

  1. AThe driving force for sintering is the reduction in surface energy as the surface area of the particles decreases
  2. BSurface diffusion and evaporation–condensation also bring the particle centers closer together, so they densify the compact substantially
  3. CThe finer the particles, the higher the temperature needed for sintering
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Answer: A. The driving force for sintering is the reduction in surface energy as the surface area of the particles decreases

A powder compact has a large surface area and carries excess surface energy. At high temperature, material moves, the necks between particles grow, and the reduction in surface area lowers the energy of the system; this is the driving force for sintering. Of the transport mechanisms, those that carry material from the grain boundaries by grain boundary diffusion or volume diffusion bring particle centers closer together and so produce densification (shrinkage). Surface diffusion and evaporation–condensation, on the other hand, only thicken the necks without bringing particle centers closer, and contribute little to densification. Finer particles have a larger specific surface area and shorter diffusion distances, so sintering proceeds at lower temperatures.

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