An intense interaction between sintered LaB6 and atmospheric oxygen began at close to 700C. The mechanism of the process and the composition of the interaction products changed, depending upon temperature. The oxidation resistance at up to 1200C was satisfactory. At higher temperatures, catastrophic oxidation of the material, caused by active evaporation of boron oxide, occurred.

High-Temperature Oxidation of Sintered Lanthanum Hexaboride. Gogotsi, Y.G., Kotlyar, D.A., Kresanov, V.S., Morozov, V.V.: Soviet Powder Metallurgy and Metal Ceramics, 1987, 26[11], 914-7