Hot-pressed samples were oxidized in air at 873 to 1473 for 8h. The samples exhibited two distinct oxidation behaviors depending upon the exposure temperature. At temperatures below 1273K, parabolic weight gains were observed as a result of the formation of amorphous B2O3 and B3LaO6. At temperatures above 1273K, crystalline La2O3 was formed together with gaseous B2O3. In this case, the surface was covered with crystalline La2O3 and flower-like B2O3 as well as B3LaO6. The oxide layer cracked severely during cooling after oxidation, due to thermal expansion mismatch between the oxide layer and the substrate.

Oxidation Behaviors of Hot-Pressed Lanthanum Hexaboride at Elevated Temperatures. Zheng, S.Q., Yu, H.S., Du, C.T., Min, G.H., Zou, Z.D.: Journal of Materials Science Letters, 2002, 21[23], 1829-31