Types of Silicon Nitride

Types of Silicon Nitride
Since the material properties strongly depend on the fabrication method, silicon nitride cannot be considered as a single material. The three main types of silicon nitride are:

Reaction bonded silicon nitride (RBSN)
Hot pressed silicon nitride (HPSN)
Sintered silicon nitrides (SSN)
Reaction bonded silicon nitride is made by direct nitridation of a compacted silicon powder, and because of the difficulty of ensuring complete reaction, it is hard to achieve a high component density.  Usual densities are in the range 2300 - 2700kg.m-3 compared with 3200kg.m-3 for hot pressed and sintered silicon nitride.  The higher density gives the HPSN and SSN materials better physical properties and means they are used in more demanding applications.  The nitridation produces only a small volume change, which means that RBSN components do not need to be machined after fabrication and complex near net shapes can be produced in a single process stage.