Investigation of high-temperature oxidation of lanthanum hexaboride in oxygen and the effect of internal oxidation on the protective properties of the scale

The vacuum microbalance method, as well as petrographic and x-ray phase analysis were employed to investigate the oxidation of lanthanum hexaboride as a function of temperature (700–1200°C), oxygen pressure (0.1–740 Torr) and porosity of the sample. It has been established that LaB₆ is highly resistant to oxidation in oxygen up to a temperature of 1200°C. The protective properties of the scale are determined by the peculiarities of the process of internal oxidation, during which a lower lanthanum boride, LaB₄, was observed to be enveloped by the vitreous oxide phase, B₂O₃.