Production of Nonoxide Powders

Nonoxides such as carbides and nitrides do not occur in nature. They are to be produced by chemical methods. SiC is produced, for example, by reacting Si02 with carbon in the form of coke. The reaction is represented by Equation 12.28. 

By taking both Si02 and coke in a powder form, the resulting SiC will also be in the form of a powder. The chemical reaction can also be a direct combination of the reactants. For example, A1 and N2 can be directly combined to form AIN. The reaction is represented by Equation 12.29. 

The resulting solid will have to be mechanically comminuted to produce the powder. 

The next type of chemical method to produce nonoxide powders is the liquid-phase reaction. An example for this method is the production of silicon nitride powder. For this, silicon tetrachloride and liquid ammonia are reacted. Silicon tetrachloride is liquid at room temperature. The reaction gives rise to silicon diimide. After this reaction, the obtained silicon diimide is decomposed to get the silicon nitride powder. Equation 12.30 shows the decomposition reaction. 

This decomposition reaction, which is a calcination process, is controlled to get the powder with the desired properties. By carrying out the process at low temperatures, we can produce fine-grained equiaxed powder particles. If the calcination temperature is above 1500°C, we get needle-like and coarse-grained hexagonal particles. 

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Until recently, the industrial production of nonoxide powders was predominantly based on two different high-temperature processes carbothermal re-... 

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