Silicon nitride (Si3N4) is a non-oxide structural ceramic material that is usually black or dark grey in colour, Silicon nitride can be made by heating silicon powder in nitrogen or reacting silicon halide with ammonia. Except for hydrofluoric acid, it does not react with other inorganic acids. It has strong corrosion resistance and is resistant to oxidation at high temperatures.

Properties of a silicon nitride

Some silicon nitrides are highly porous and therefore have low density and oxidation resistance. When treated properly, silicon nitride offers good hardness at extremely high temperatures, good creep resistance, high wear resistance, low coefficient of thermal expansion, chemical resistance, oxidation resistance, and increased mechanical strength

1. It has good corrosion resistance, thermal shock, and abrasion resistance. It can be used at temperatures below 1900 degrees Celsius.

2. It has excellent split endurance, very stable chemical composition, and thermal conductivity.

3. The product contains nitrides, which have the characteristics of low expansion rate, high thermal conductivity, and high strength, and almost no shrinkage when heated.

4. High strength and wear resistance.

5. High-temperature oxidation resistance. An oxide film will be formed on the surface after long-term use, and the internal materials can be protected from chemical reactions.

Application Of Silicon Nitride

Silicon nitride has very good applications in steel smelting, refractory materials such as reciprocating engine components, bearings, metal processing, etc. It is also widely used in normal temperature and high temperature sealing abrasives such as wear-resistant rubber, plastics, and ceramics.

Automotive industry

The biggest application of silicon nitride is found in the automotive industry, particularly the various wear and combustion parts in reciprocating engines where stresses at high temperatures are prevalent. In diesel engines, silicon nitrides are used in glow plugs (for quicker start-up time), precombustion chambers (to reduce emissions or act as a muffler), and turbochargers (to reduce engine lag). Silicon nitride is also used in cam followers, tappet shims, precision shafts and axles.

Bearings

Silicon nitride ceramic ball and roller bearings are preferred over steel for high-temperature applications. This prolongs the bearing life at higher speeds as it would possess better corrosion resistance. Its higher modulus of elasticity compared to steel indicates that it is more rigid, thus creating a smooth motion and less vibration with the contacting surfaces.

Metalworking
Silicon nitride is also utilised in metal cutting tools for cast iron, hard steel, and nickel-based alloys due to its hardness, fracture toughness, and thermal shock resistance.

Industrial applications

Another application is handling molten metal – for which metallic components are often unsuitable. Weld jigs/positioners, spray nozzles, cylinder wall coatings, turbine rotor, blades, pipes for rockets, and missiles employ silicon nitride for its strength, electrical properties and shock resistance. Applications in the aluminium casting industry, as well, benefit from silicon nitride’s good corrosion resistance, thermal shock resistance, and thermal conductivity. These include heating tubes, pump liners, riser tubes, and thermocouple protection sheaths.