The oxidation of LaB6 ceramic powder was investigated. The powder samples were heated continuously from room temperature to 1473K at a heating rate of 10K/min by differential scanning calorimetry. Oxidation tests were conducted at various exposure temperatures. The phases and morphologies of the samples before and after exposure were analyzed by XRD and SEM. It was pointed out that LaB6 had a high oxidation resistant below 1273K due to the fact that the oxide layer hindered oxygen diffusion to the surface of the LaB6 grains. The oxide layer was composed of transition phases, which comprised La2O3 and B2O3 formed from the initial oxidation. When the oxidation temperature exceeded 1273K, the protective layer was destroyed due to vaporization of liquid B2O3. Based upon the results of X-ray diffraction analysis, the oxidation process was that lanthanum borate, La(BO2)3, formed on the surface of samples below 1273K, while La2O3 and B2O3 were present on the surface of samples oxidized at 1473K.

Oxidation Process of Lanthanum Hexaboride Ceramics. Zheng, S., Min, G., Zou, Z., Yu, H., Han, J., Wang, W.: Rare Metals, 2002, 21[2], 101-5