Structural and compositional analyses of oxidised layers of ZrB2-based UHTCs

ZrB2 based UHTCs (ZrB2/20 vol.% SiC) with rare earth additions (La2O3, LaB6 and Gd2O3) were oxidised for 1 h at 1600 °C and the oxidised layers analysed by FIB-SIMS and TEM techniques. Rare earth elements added to ZrB2/20 vol.% SiC led on oxidation to formation of a thick (up to ∼350 μm) protective oxide layer. Detailed cross-sectional analyses of oxidised layers revealed that they comprised of mixed crystalline and amorphous phases: m-ZrO2 and zirconates were formed on the oxidised surfaces in all samples as well as evidence of immiscible liquid.