Synthesis, densification and oxidation study of lanthanum hexaboride

Abstract This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB 6 . LaB 6 was synthesized by boron carbide reduction of La 2 O 3 . Effect of temperature on product quality was investigated. Pure LaB 6 powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB 6 powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB 6 was measured as 20 GPa and 3.02 MPa m 1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB 6 surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.