Silicon nitride ceramic is a range of advanced engineering ceramic characterized by high strength, toughness and hardness and excellent chemical and thermal stability.
The different types of silicon nitride, RBSN, HPSN, SRBSN and SSN, result from their methods of fabrication, which governs their resulting properties and applications. Here is an introduction to these 4 types of silicon nitride ceramics.
Reaction-bonded silicon nitride (RBSN) is made by carefully nitriding a silicon (Si) ‘dough’ or compact at about 1450°C. During the reaction, the Si3N4 grows in the porosity in the compact. This results in little dimensional change accompanied by an increase in density. This feature is the biggest benefit of RBSN, as it often allows parts to be made to near net shape without the need for subsequent expensive grinding operations.
A consequence of this reaction is that the final product contains porosity and as such its mechanical properties are inferior to those of the other types of silicon nitride ceramic, as shown in the table below. However, the material is relatively cheap to produce and has found application particularly as kiln furniture.
Hot pressed silicon nitride (HPSN) has found application as cutting tools for example. Applications tend to be for simple shapes as the hot pressed ‘billet’ must be diamond ground to obtain the required profile. As a result HPSN parts tend to be expensive and have largely been superseded by SSN.
More recent developments of sintered reaction-bonded silicon nitride (SRBSN) have shown improvements to toughness and impact resistance as a result of the growth of crack deflecting silicon nitride ceramic needle-like grains.
Sintered Silicon Nitride (SSN) covers silicon nitride ceramic materials which are densified by pressureless sintering in a nitrogen atmosphere at around 1750°C. . In order to aid densification, various combinations of sintering additives such as yttrium oxide, magnesium oxide and aluminum oxide are used. SSN and sialon generally offer the best mechanical properties available for a silicon nitride and are the most widely used in industrial applications such as molten metal handling, industrial wear, metal forming, the oil and gas industries and the chemical and process industries.
Thanks for reading this passage and hope that you now have a basic understanding of 4 types of silicon nitride ceramics. Advanced Ceramic Materials (ACM) is a leading precision ceramic manufacturer based in Lake Forest, California. If you feel interested about the silicon nitride ceramic products, you can send us an inquiry or contact us via [email protected]