Sintering and oxidation of GdB4 synthesized by B4C reduction method

Abstract

Gadolinium tetraboride (GdB4) was synthesized by reduction of Gd2O3 using boron carbide in presence of carbon. Effect of temperature on product quality was investigated. Pure GdB4 powder was obtained in vacuum at 1500oC. Pressureless sintering experiments revealed that sintering takes place only above 1600oC. A maximum density of 77.1% of the theoretical value was obtained at 1800oC by pressureless sintering. Hot pressing resulted in 95.5% of theoretical density at the lower temperature of 1700oC under 35 MPa pressure. Hardness and fracture toughness of dense GdB4 were measured and found to be 21.4 GPa and 2.3 MPa·m1/2, respectively. After exposure to air at 900oC, the formation of a porous and non-protective oxide layer was observed.