Synthesis of boron suboxide (B 6O) with ball milled boron oxide (B 2O 3) under lower pressure and temperature

Boron reacted with ball milled boron oxide under pressures between 1 and 5 GPa and at temperatures between 1300 and 1700 °C to afford boron suboxide (B 6O). Icosahedral B 6O grains with diameters ranging from 100 nm to 1.3 μm were prepared. The factors that affect the synthesis of B 6O are investigated. The best sample with crystal size up to 1.3 μm is obtained at 2 GPa and 1400 °C for 6 h. The indentation experiment gave an average Vickers hardness of 32.3 GPa for bulk B 6O sample, which is consistent with previous reports. Bulk B 6O sample exhibits oxidation resistance in air up to 1000 °C and mild oxidation in the temperatures of 1000–1200 °C, which is more oxidation resistant than diamond. It is possible that B 6O could be used as a substitute for diamond in industry because of its relatively mild synthesis conditions, high thermal stability and high hardness. Icosahedral B 6O grains were prepared for mixtures of boron and ball milled boron oxide at 2 GPa and 1400 °C, a milder synthesis condition in comparison with previous works [Display omitted] .