Ceramics - Silicon Nitride

Silicon nitride does not occur naturally. Most of the powder commercially available has been produced by reacting silicon metal powder with nitrogen at temperatures between 2,282°F (1,250°C) and 2,552°F (1,400°C). The powder that is removed from the furnace is not ready to use. It is loosely bonded and must be crushed and sized. The resulting powder contains impurities of Fe, Ca, and Al. Higher purity silicon nitride powder has been produced by reducing SiO₂ with carbon in a nitrogen environment, and by reaction of SiCl₄ with ammonia; these reactions produce a very fine powder. High purity silicon nitride powder has also been made by laser reactions in which a mixture of silane (SiH₄) and ammonia is exposed to laser light from a CO₂laser. This produces spherical particles of silicon nitride of very fine size.