Factors Affecting Solid State Sintering

Factors Affecting Solid State Sintering
Typically a solid-state sintered ceramic is an opaque material containing some residual porosity and grains that are much larger than the starting particle sizes. On the basis of the discussion and models just presented, it is useful to summarize
the more important factors that control sintering, Implicit in the following arguments is that theoretical density is desired.

1. Temperature.
Since diffusion is responsible for sintering, clearly increasing temperature will greatly enhance the sintering kinetics, because D is thermally activated . As noted earlier, the activation energies for bulk diffusion are usually higher than those for surface and grain boundary diffusion. Therefore, increasing the temperature usually enhances the bulk diffusion mechanisms which lead to densification.
2. Greed density
Usually, a correlation exists- between the green (prior to sintering) density and the final density, since the higher the green density, the less pore volume that has to be eliminated.
3. Uniformity of green Microstructures
More Important than the green density is the uniformity of the green microstructure and the lack of agglomerates . The importance of eliminating agglomerates is discussed in greater detail below.
4. Atmosphere
The effect of at atmosphere can be critical to the densification of a powder compact. In some cases, the atmosphere can enhance the diffusivity of a rate-controlling species, e.g, by influencing the defect structure. In other cases, the presence of a certain gas can promote coarsening by enhancing the vapor pressure and totally suppressing densification .
Another important consideration is the solubility of the gas in the solid. Because the gas pressure within the pores increases as then shrink ,it is important to choose a sintering atmosphere gas that readily dissolves in the solid.