Oxidation of Silicon Carbide Ceramics Obtained by Liquid Phase Sintering

In this work, silicon carbide ceramics were developed by liquid phase sintering using AlN-Y2O3 as additive. Two compositions were obtained using SiC powders and different contents of AlN-Y2O3. The powders were mixed/homogeneizated and subsequently dried and deagglomerated. Powder mixtures were compacted by cold isostatic pressing. Samples were sintered at 2080oC, for 1h, under 0.2 MPa-N2 atmosphere. Sintered samples were characterized by X-Ray diffraction and density. The oxidation behavior was investigated and related to the densification and additive-content. Samples were submitted to the tests at 1200, 1300 or 1400oC, in air for 120 hours. Weight gain of the samples is plotted as function of the exposure time, obtaining the evolution of the oxidation on the surface of the samples. Based on the results, the parabolic oxidation content (kp) and activation energy were determined. The results indicate that the samples present parabolic behavior in all conditions. The activation energy results indicate that the phenomena of diffusion of oxygen ions into the oxide layer and interfacial reactions between oxide layer and intergranular phase are the responsible for oxidation mechanism.