Oxidation behavior and kinetics of (Zr, Ti)(C, N)–SiC ceramics with enhanced oxidation resistance at 850 °C–950 °C

Abstract

The oxidation behavior and kinetics of (Zr, Ti)(C, N)–SiC ceramics subjected to a temperature of 850 °C-950 °C (typical operating temperatures range of Generation-IV nuclear reactors) for 1–4 h are investigated via X-ray diffraction, scanning electron microscopy, and weight gain testing. The results show that the microstructures of the ceramics after oxidation comprises primarily of m-(Zr, Ti)O2, c-(Zr, Ti)O2, and SiO2. After adding Si, the oxidation layer appears as a two-layer structure with both external and internal layers. The oxidation order of (Zr, Ti)(C, N)–SiC ceramics at 850 °C-950 °C is ZrSi > (Zr, Ti)(C, N) > SiC. Unoxidized SiC forms a “core-shell” structure with a dense external layer of SiO2. The dual effect of small SiO2 particles occupying cracks and the “core-shell” structure of SiC–SiO2 withstanding stresses can inhibit the propagation of cracks and reduce the porosity of the oxide layer. The oxidation of Z5T and Z5T5S exhibits linear oxidation kinetics, whereas the oxidation of Z5T10S and Z5T20S results in quasi-parabolic oxidation. By adding Si, the oxidation activation energy of Z5T20S (with the addition of 20 mol% Si) increases by 174 % compared to that of Z5T ceramic, thus improving the oxidation resistance of (Zr, Ti)(C, N)-based ceramics at 850 °C-950 °C.