Silicon nitride is a very important engineering ceramic because it can be shaped into many different shapes, each with different properties. At high temperatures, silicon nitride is very strong and rigid. It is also very resistant to wear and tear from friction and particulates. It also has excellent thermal properties, meaning it does not expand or contract when heated or cooled. Finally, silicon nitride is very resistant to most acids and alkalis, corrosive gases and liquid metals. Rolling fatigue (RCF) tests of several ceramic materials used in high-performance bearings have shown that only fully dense silicon nitride is better than bearing steels.
The fully dense Si3N4 bearing materials have shown that the RCF is ten times the durability of high-performance bearing steel. It also reduces the centrifugal load on the outer raceways of these rotating bodies at high speeds. Ceramics are also very durable and do not succumb to destruction or deformation under heavy pressure. Silicon nitride is also very difficult to break or deform, making it very useful in a wide variety of situations.
In addition to strength, silicon nitride is also a good conductor of heat. This is important for industrial applications where extreme temperatures are used. Silicon nitride has a unique chemical composition and microstructure that makes it conduct heat worse than metals.
