A study based upon kinetic investigations and metallographic examination was made of high-temperature oxidation in air at 500 to 1200C. On the basis of thermodynamic calculations of equilibria in the systems, LaB6-oxygen (nitrogen) at 298 to 2000K, it was established that - from the thermodynamic point of view - LaB6 was unstable in oxygen and nitrogen atmospheres. It was also found that, during oxidation, the most probable reactions were those resulting in the formation of La2O3 and B2O3. Reactions which yielded lanthanum and also La2O3 and free boron were also thermodynamically probable. At the internal scale/LaB6 interface, the existence of LaB4 was detected. This constituted an intermediate oxidation product of the starting hexaboride. It was shown that, during oxidation of LaB6, an unknown phase (possibly LaB6 with increased boron content) was formed.

High-Temperature Oxidation of Lanthanum Hexaboride. Voitovich, R.F., Pugach, E.A.: Soviet Powder Metallurgy and Metal Ceramics, 1973, 12[2], 145-8