Synthesis of boron carbide powder in relation to composition and structural homogeneity of precursor using condensed boric acid–polyol product

Crystalline boron carbide (B4C) powder was synthesized by the carbothermal reduction of boron oxide (B2O3) using a condensed boric acid (H3BO3)-mannitol product. The condensed product was prepared by the dehydration condensation of H3BO3 and mannitol at several molar ratios. The composition of the precursor was controlled by thermal decomposition in air before the carbothermal reduction of the condensed product, which had a homogeneous structure but an excessive carbon component compared with that required for the carbothermal reduction. B4C powder with less free carbon could be synthesized by heat treatment at 1250 °C for 5 h in an Ar flow of the thermally decomposed product prepared from the condensed product by thermal decomposition at 400 °C for 3 h in air. Furthermore, the structural homogeneity of the precursor affected the B4C formation behavior at the low synthesis temperature. These results demonstrated that the compatibility of the composition, the dispersibility, and the homogeneity of the B2O3 and carbon components in the precursor, which was achieved by thermal decomposition of the condensed product in air, leads to the low-temperature synthesis of crystalline B4C powder using a condensed H3BO3–polyol product.