Silicon nitride is a powder that is difficult to process. It melts at 1850 °C, and if you try to melt it at a temperature above that, it breaks down into silicon and nitrogen. This means that it is difficult to use traditional hot press sintering technology. However, the addition of other substances, such as agglomerates or binders, can help to hold silicon nitride powder together. This process, called liquid-phase sintering, takes place at a lower temperature and creates a block-like material.
But this method can introduce impurities into the final product because it involves the addition of binders or sintering agents. Another method that produces cleaner bulk materials is called spark plasma sintering. This method uses pulses of electric current that are applied for a very short time (a few seconds). This method produces compact and dense silicon nitride blocks at temperatures of 1500-1700°C.
