Oxidation behavior in wet oxygen environment of Al2O3 added reaction-sintered Si-B-C ceramics

The influence of Al2O3 addition on the oxidation behavior of Si-B-C ceramics at 1200 °C in O2/H2O (40/60) atmosphere was studied. Results showed that Al2O3 was enriched in the oxidized layer, and impeded the crystallization of oxide (cristobalite) during cooling. Denser oxidized layer and less weigh change were observed. Infrared spectra indicated that the addition of Al2O3 could weaken the tendency of bridged oxygen atoms (Si-O-Si, Si-O-Al) to become non-bridged oxygen atoms (Si-O-H) and enhance the degree of interconnection of the structural units. The above phenomenon was attributed to the fact that the bridging oxygen bond between Al and Si was not broken but protonated. The protonated bridging oxygen (Al-O(H)-Si) still acts as a linkage in the glass network, which results in higher viscosity of the aluminosilicates melt and lower reaction activity with steam, thereby significantly improving the oxidation resistance of Si-B-C in O2/H2O atmosphere.