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

Abstract

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 (32.5μm2h−1) and 1600°C (86.1μm2h−1) within 16h, but are irregular at 1700°C. The calculated Arrhenius activation energy is ca. 116kJmol−1 for 1500–1600°C/16h 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.