Oxidation behavior of LPS-SiC ceramics sintered with AlN/Y2O3 as additive

In this work, the oxidation behavior of SiC ceramics sintered with additives based on AlN-Y2O3 system was investigated. SiC ceramics doped with different AlN:Y2O3 contents of 8.4:11.6 wt.% or 2.2:17.8 wt.% were sintered at 2080 °C for 1 h under nitrogen atmosphere, obtaining ceramics with relative density near to 96% in both compositions. Samples were oxidized at 1200 °C, 1300 °C or 1400 °C in air for up to 120 h. Oxidation was monitored by the weight gain of the samples as function of exposition time and temperature. A parabolic growth of the oxidation layer has been observed and the coefficient of the growth rate has been determined by relating the weight gain and the surface area. In oxidation testing performed at 1200 °C, samples containing lower Y2O3 amounts showed greater oxidation resistance; however, by raising the temperature (to 1400 °C), the samples containing higher Y2O3 amounts showed greater oxidation resistance. The oxidized layer characterized by X-ray diffraction presented SiO2 and Y2Si2O7 as crystalline phases. Furthermore, the activation energy for oxidation of 780 kJ/mol and 405 kJ/mol for AlN:Y2O3 contents of 8.4:11.6 wt.% or 2.2:17.8 wt.%, respectively.