Densification of Silicon Nitride Ceramics by Gas Pressure Sintering

The densification and the microstructure of silicon nitride ceramics depends on processing parameters, mainly the sintering conditions and the amount and type of sintering aids necessary to promote liquid phase sintering. In this work, selected compositions of silicon nitride containing different amounts and type of sintering additives, were normal sintered at 1700°C and 1750°C, and gas pressure sintered under 25, 60 and 100 bar of nitrogen pressure, varying, also, the soaking time and final sintering temperature. Densification rates ware determined using a dilatometer coupled to the gas pressure sintering furnace. Gas pressure sintering has shown to be an effective route for densification of silicon nitride ceramics with low quantities of sintering aids. Densities greater than 99.5% of theoretical density were obtained for compositions containing only 5wt.% of sintering aids by using multiple steps of temperatures up to 1950°C and 100 bar N 2 pressure.