Abstract
HfB2–2 wt-%-La2O3, HfB2–20 vol.-%SiC and HfB2–20 vol.-%SiC–2 wt-%La2O3 were sintered by spark plasma sintering for 5 min between 1900 and 2000°C. Oxidation studies were carried out in static air on sintered ultra high temperature ceramics at 1600, 1800 and 2000°C, and the weight change and microstructure changes after oxidation were examined. LaBO3 formed on the surface after oxidation for 1 h above 1600°C in all La2O3 containing materials, and the cross-section microstructure shows growth of LaBO3 fibres from pores due to vapour phase reaction. Addition of La2O3 altered the oxidation kinetics of HfB2, significantly increasing the oxidation layer thickness above 1600°C. However, above 1800°C reaction has occurred between the sample and the zirconia crucible.
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