Grain coarsening in gas pressure sintered silicon nitride

The grain growth of silicon nitride sintered by GPS has been studied in the case of an α-rich initial powder. As time increases, the microstructure becomes bimodal. A few large grains grow abnormally at the expense of the smallest ones. The growth rate of the major portion of grains is slow and can be assimilated to a normal growth with interface-reaction control. This rate limiting mechanism has been determined by three different methods: a method based on the Kingery’rate laws, a more direct method based on the variation of the grain size vs. the amount of the liquid phase and considerations on grain morphology according to Lee.