Synthesis, densification and oxidation study of lanthanum hexaboride

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB6. LaB6 was synthesized by boron carbide reduction of La2O3. Effect of temperature on product quality was investigated. Pure LaB6 powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB6 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 LaB6 was measured as 20 GPa and 3.02 MPa m1/2 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 LaB6 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.