The effect of Al2O3 on the high-temperature oxidation resistance of Si-B-C ceramic under air atmosphere

Si-B-C ceramics were prepared through reaction sintering, and the influence of Al 2 O 3 addition on the high-temperature (1100-1300°C) oxidation behavior of the material under air atmosphere was studied. The erosion behavior and mechanism are determined from the measurement of weigh changes, microstructure observations, and characterization of the generated oxides on postexposure specimens. Results show that Al 2 O 3 is enriched in the oxidized layer, inhibiting the volatilization of B 2 O 3 and impeding the crystallization ability of oxide (cristobalite). Narrower erosion layer and less weigh change are observed with Al 2 O 3 . Low-frequency Raman results reveals that with the increase in Al 2 O 3 , the bending vibrations of the BO 4 units and B-O-B stretching of the metaborate ring relative intensity are enhanced. Furthermore, high-frequency Raman results shows that the relative proportion of high-dimensional vibration modes Q 3 and Q 4 which result in a higher viscosity of melt and a greater resistance of oxygen diffusion are positively correlated with Al 2 O 3 .