Nucleation silicon nitrides

These experimental data suggest that P-SijN4 nucleation has no influence on the microstructure of silicon nitride materials under common sintering conditions and using common powders. 

As a consequence, the network of grains must move apart, giving rise to dilatational stresses which are responsible for cavitation within the material. Cavitation occurs when the dilatational stress at a multigrain junction exceeds a critical stress for cavity nucleation. Subsequent cavity growth occurs via redistribution of the secondary phases from the cavity towards the uncavitated material. As the secondary phase flows away from the cavitated junction, the stress required for cavity nucleation relaxes, thus releasing the stressed contacts between silicon nitride grains. The rearrangement of dilatation stresses then results in a new round of cavity formation. 

When pure silicon is used, the grain surface combines with nitrogen producing a nitride surface layer by nucleation and diffusion mechanisms. This process is slow, but may be accelerated above the melting point of silicon, which is transferred as a liquid in the system. 

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