The dispersion state of boron oxide (B 2 O 3 ) and carbon components in a precursor prepared from a condensed boric acid (H 3 BO 3 )-polyol product by thermal decomposition in air was found to be closely related to the formation of boron carbide (B 4 C) powder at a low synthesis temperature. The microstructure in the precursor was fabricated by controlling the composition of a condensed H 3 BO 3 -poly(vinyl alcohol) (PVA) product. The size of B 2 O 3 particles dispersed in the carbon matrix of

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... he microstructure decreased with increasing PVA content of the condensed product. Crystalline B 4 C powder with a little free carbon was synthesized from a precursor with a more finely and homogeneously dispersed structure consisting of B 2 O 3 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 B 4 C particles were promoted even at a low synthesis temperature.