Microstructure in precursor formed by controlling composition of condensed boric acid-poly(vinyl alcohol) product for low-temperature synthesis of boron carbide powder

Abstract

The dispersion state of boron oxide (B2O3) and carbon components in a precursor prepared from a condensed boric acid (H3BO3)-polyol product by thermal decomposition in air was found to be closely related to the formation of boron carbide (B4C) powder at a low synthesis temperature. The microstructure in the precursor was fabricated by controlling the composition of a condensed H3BO3-poly(vinyl alcohol) (PVA) product. The size of B2O3 particles dispersed in the carbon matrix of the microstructure decreased with increasing PVA content of the condensed product. Crystalline B4C powder with a little free carbon was synthesized from a precursor with a more finely and homogeneously dispersed structure consisting of B2O3 particles and the carbon matrix by heat treatment at 1200°C for 5 h in an Ar flow. Furthermore, the formation and subsequent grain growth of B4C particles were promoted even at a low synthesis temperature.