1981 Volume 89 Issue 1027 Pages 148-155
Hot-pressed β′-sialon (z=1-4) and reaction sintered β′2 “balanced” sialon were prepared from commercial grade Si3N4, SiO2 and AlN powder. Densities of sialon were 2.853 (z=1), 3.108 (z=2), 2.980 (z=2, RS), 3.095 (z=3) and 3.110g/ml (z=4). Specimens were oxidized in dry oxygen at temperature 1200° and 1300°C for up to 720h (30d), and characterized by measurements of weight gain, X-ray diffraction, EPMA, SEM and microscopy. The main oxidation products were mullite and cristobalite which formed around internal pores and surface (stage 1), and eventually as a relative dense oxidized layer (stage 2). The weight gain in each stage is proportional to (time)1/2 and erratic point between stage 1 and stage 2 appear at about 168h (7d). The rate of oxidation in each stage increases with increasing temperature. The weight gain of oxidized samples are as follows:
β1′>β2′>β3′>β4′ But the mean thickness of oxidized layer, as contrasted with the weight gain, are as follows: β1′<β2′<β3′<β4′
