The quality of energy is evaluated by "Exergy". By contrast to the amount of energy preserved, the exergy is irreversibly consumed. The balance of consumed raw materials, energy and exergy in the synthesis process of silicon nitride ceramics that are made from silicon nitride or silicon powder is quantified. The input exergy is reduced by using Si powder as the main raw material with sintering additives of ZrO(2) and spinel. In the manufacturing process of silicon nitride, the majority of the input exergy is consumed in the sintering step. The relationship between the input exergy in sintering step and the sintering temperature, holding temperature as well as the total time is analyzed by a regression method, which gives a guideline for the rationalization of the manufacturing process.

Keywords: Silicon nitride; Process; Exergy; Reaction-bonding