Oxidation and corrosion of silicon nitride ceramics with different sintering additives at 1200 and 1500 °C in air, water vapour, SO2 and HCl environments – A comparative study

The effect of different sintering additives on the high temperature oxidation and corrosion behaviour of silicon nitride based ceramics was investigated. Comparative tests were conducted at 1200 and 1500 °C in air, in water vapour, and with the highly corrosive gases HCl and SO2. Si3N4 was prepared with MgO, Al2O3, Y2O3 and Al2O3 + Y2O3 sintering additives. Hot pressed discs were tested for a total time of up to 128 h. The electrically conductive ceramic composites Si3N4 + TiN and Si3N4 + MoSi2 were also tested under the same conditions. The effects that the different corrosion environments have on the different ceramics are presented. SEM studies of the oxidised ceramics show the direct transformation of Si3N4 grains into SiO2 through a reaction interface layer.