Oxidation Behavior of Spinel/Silicon Carbide Whisker Composite Ceramics

Oxidation behavior of a spinel (Mg2Al4O8) composite containing 30vol% SiC whisker has been studied at 1300°C in air. The weight gain curve obeyed the parabolic law up to the oxidation time of 120h, indicating that the oxidation rate was controlled by diffusion of oxygen in the matrix. Bending strength of the oxidized composite increased appreciably with the oxidation time up to 5h but degraded to 70% of the initial strength after the oxidation for 120h. Grain sizes of crystals and cracks formed in the oxidized layer became larger with the oxidation time. Periclase (MgO) and a small amount of α-cordierite (Mg2Al4Si5O18) as well as the spinel and β-SiC were observed in the layer.