Synthesis of chromium borides by solid-state reaction between chromium oxide (III) and amorphous boron powders

Abstract

Solid-state reactions between ultrafine ehromia powder, which was produced by the thermal decomposition of chromium formate, and amorphous boron powder, were carried out in a vacuum of 10-2 to 10-3 Pa at temperatures of 600° to 1600°C for 2h. In the reactions at B/Cr2O3 mole ratios of 1.5 to 7.0 and 1600°C, five kinds of chromium borides: Cr2B3, CrB, Cr2B4, Cr2B3 and CrB2, were obtained. Single phases of CrB and CrB2 were obtained at the mole ratios of 3.0 and 7.0, and at 1600° and over 1000°C, respectively. The chemical compositions of the single phases of CrB and CrB2 were Cr».MB and Cro.MBj, respectively. Lattice parameters of the chromium borides are as follows: CrB; a=0.2967(1)nm, b=0.7868(1)nm, c=0.2932(1)nm, V=0.0684(6)nm3: CrB2; a=0.2973(1)nm, c=0.3072(3)nm, V=0.0235(3)nm1.