High temperature oxidation kinetics of amorphous silicoboron carbonitride monoliths and silica scale growth mechanisms determined by SIMS

The highly dense, amorphous silicoboron carbonitride (Si-B-C-N) monoliths provide superior oxidation resistance above 1600 °C, but the in-depth oxidation kinetics are unknown. Here oxidation kinetics of amorphous Si-B-C-N monoliths was investigated by one-step oxidation (in flowing ¹⁶O-rich air) over 1500–1700 °C. Coincidently, the growth mechanisms of oxide scales on ceramic surfaces were studied by oxidizing ceramics in ¹⁸O-rich air followed by ¹⁶O where ¹⁶O was used as an equivalent isotopic tracer and the distributions of ¹⁶O and ¹⁸O in oxide scales were determined directly by secondary ion mass spectrometry (SIMS). The thickness changes of silica scales fit well to parabolic rules at 1500 °C (32.5 μm² h⁻¹) and 1600 °C (86.1 μm² h⁻¹) within 16 h, but are irregular at 1700 °C. The calculated Arrhenius activation energy is ca. 116 kJ mol⁻¹ for 1500–1600 °C/16 h oxidation. The relative concentration profiles of ¹⁶O from SIMS analysis indicate growth of oxide scales is mainly by oxygen lattice diffusion inside scales during oxidation of the amorphous Si-B-C-N ceramics.