Two kinds of boron carbide powders, S-1 and S-2, were prepared by the reaction of boric oxide with carbon black in magnesium (2B2O3+6Mg+C=B4C+6MgO). Powder S-1 was prepared by heat-treating for 10min at 1500°C immediately after the reaction was completed, while S-2 was prepared by heat-treating at 1650°C. After purifying the powders, the chemical composition of