Formation of Carbon Free B4C through Carbothermal Reduction of B2O3

Abstract

The occurrence of residual carbon during carbothermal reduction synthesis of B4C was investigated using boric oxide (B2O3) and carbon black (C) reaction mixtures with less than stoichiometric carbon (with B: C molar ratios of 4: 2.66, 4: 2.0 and 4: 0.833). The reaction was studied in 1 atm argon in a temperature range of 1300° to 1625°C for 0.5 h. The reaction mixture with B: C = 4: 2.66 was also found to form residual free carbon. Addition of a small quantity of K2CO3 to reactant mixture was found to decrease the free residual carbon. No peak, corresponding to free carbon, was observed in B4C formed with boron and carbon in the ratio of 4: 2. When the carbon content in the reactant mixture was decreased to a very low value (B: C = 4: 0.833), no B4C could be formed and the B2O3 was found lost totally. The B4C powder was found to have uniform size and needle like shape which was also observed to be influenced by K2CO3 addition to the reaction mixture.