Processes
Silicon nitride (Si3N4) can be produced by various methods: sintered, using hot isostatic press or reaction bonded. In its sintered or pressed forms, it is obtained from a Si3N4 powder, mixed with organic binders, obtained in advance by nitriding the silicon powder (process combining a rise in temperature with a nitrogen-based gaseous environment). In its reaction bonded form, the silicon nitride is formed by pressing or injection moulding, then undergoes a nitriding process.
Properties
Silicon nitride is one of the hardest and most resistant ceramics.
The main characteristics of silicon nitride are: low density, excellent resistance to thermal shocks, excellent resistance to wear, excellent resistance to corrosion (liquids and gas), low thermal expansion coefficient, low wetability against molten metals, and also good electrical insulation.
Applications
The grades of sintered and pressed silicon nitride are mainly intended for thermomechanical applications, or resistance to corrosion. Reaction-bonded silicon nitride is mainly used in foundries, resistance welding or TIG welding applications, but also in mechanical applications due to its very high resistance to wear.
It is most widely used in the following applications: ring faces for mechanical seals, pump and valve components, heating tubes for thermocouples, welding pins and nozzles, tools for semi-conductor processing equipment, ball-bearings, etc.