Synthesis of nano particles and fiber-like shape boron carbide powder from ploy (vinyl alcohol) and boric acid

Abstract

Boric acid solution was dropwise added to poly vinyl alcohol (PVA) solution under a hot condition (80 °C) and stirring. The condensation reaction was controlled by extracting of a white poly vinyl borate (PVBO) gel precursor which formed on the surface of the reaction mixture. By collecting of the gel several times during the reaction, the solution viscosity and concentration of the reacting mixtures was decreased, and the interface between the reactants was increased, resulting in a high dispersion of C-B at the nanometer scale. After drying of the PVBO precursor, the C/B2O3 molar ratio was controlled at (3.1–2.9), which is less than the stoichiometric ratio of 3.5, by the pyrolysis of the precursor at 650 °C for 2 h in air. The X-ray diffraction (XRD) analysis of the final product show that high purity semi-equiaxed grains and fiber-like shape nanocrystalline boron carbide powder was synthesized by the heat treatment of the pyrolyzed precursor at 1400 °C for 4 h in Ar flow. Compared to previous reports, it is the first time to report the formation of a fiber-like shape boron carbide by carbothermal reduction route at a low temperature as 1400 °C.