The oxidation behaviour of a porous Si2N2OZrO2 composite material

Abstract The oxidation behaviour of a low-cost, porous Si 2 N 2 O-ZrO 2 composite material produced without the use of sintering aid was investigated in air between 1000 and 1520 °C. The extent of internal oxidation was found to be dependant on the oxidation temperature. At temperatures ≤ 1300 °C considerable internal oxidation of the material occurs with concommitant large weight gains. The material exhibits excellent oxidation resistance at high temperatures (>1300 °C) and the higher the oxidation temperature the lower the weight gain. A very thin layer of oxide primarily consisting of ZrSiO 4 forms on the internal pore walls which, together with the surface oxide layer, protects the material from further oxidation. At 1300 °C the stresses induced in the matrix by the volume expansion of the oxidation products cause severe cracking of the material on cooling from the annealing temperature. Following oxidation exposures at temperatures ≥1300 °C the unstabilised ZrO 2 phase in the matrix is inhibited from undergoing the t-m transformation. This is most probably due to the dissolution of nitrogen in ZrO 2 resulting in the stabilised, non-transformable t′ -ZrO 2 phase.