The effect of the boron oxide (B 2 O 3 )/carbon arrangement of the precursor on the low-temperature synthesis of boron carbide (B 4 C) powder was investigated in this study. The precursor was prepared by low-temperature heat treatment without thermal decomposition and subsequent pyrolysis in air of the condensed product formed from poly(vinyl alcohol) (PVA) and boric acid. The dispersion state of B 2 O 3 particles in the carbon matrix of the precursor significantly affected the acceleration of the synthesis reaction. Crystalline B 4 C powder with little free carbon was obtained by heat treatment at 1100°C, which was also the critical formation temperature, for 20 h in an Ar flow starting from a precursor with a B 2 O 3 /carbon structure homogeneously arranged at the nanometer scale.

Crystalline boron carbide (B4C) powder was synthesized by the carbothermal reduction of condensed products formed from boric acid (H3BO3) and polyols with different molecular characteristics, i.e., glycerin, mannitol, and poly (vinyl alcohol) (PVA). The effect of the molecular structure of the polyol on the thermal decomposition conditions and the obtained morphology of the B4C powder was discussed in this study. The thermal decomposition in air of each condensed product was performed before the carbothermal reduction in order to eliminate the excess carbon, where the decomposition conditions varied with the type of polyol. Crystalline B4C powder with less residual free carbon was synthesized from the thermally decomposed products by heating at 1250 °C for 5 h in an Ar flow. The thermal decomposition conditions and the particle size of the obtained B4C powder reflected the molecular characteristics of the polyols.