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 (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 the 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.

Low-temperature carbothermal nitridation of boron oxide induced by networked carbon structure

“…The morphology of micrometer-size grains is similar to that of B 4 C particles prepared from a condensed H 3 BO 3 -PVA product. 8), 11) On the other hand, the morphology of nanoparticles on grains is similar to that of the obtained BN powder in this study (Fig. 7).…”

“…8), 11) The formed B 4 C is converted to BN by increasing the heat treatment time, implying the high reactivity of B 4 C microparticles formed from our precursor. The powder form of the B 2 O 3 /carbon precursor, not a pellet, is also conducive to the acceleration of the BN formation reaction according to Eq.…”

Low‐Temperature Synthesis of Calcium Hexaboride Powder via Transient Boron Carbide Formation

“…Nanosize B 2 O 3 particles (approximately 100 nm) were homogeneously dispersed in a carbon matrix. Our previous study revealed that a thermally decomposed product prepared from a condensed H 3 BO 3 ‐PVA product, consisting of B 2 O 3 and carbon components (B 4 C precursor), exhibited the dispersion of B 2 O 3 nanoparticles in a carbon matrix …”

“…To achieve this approach, we focused on our low‐temperature synthesis method for B 4 C powder . This method is described as follows: a B 4 C precursor consisting of B 2 O 3 and carbon components is prepared from a condensed boric acid (H 3 BO 3 )‐polyol product by thermal decomposition in air.…”

“…The carbon content in the precursor (C/B 2 O 3 ratio) is controllable by varying the thermal decomposition conditions in air. Within the obtained precursor powder, a B 2 O 3 /carbon structure with a homogeneous arrangement at the nanometer scale is spontaneously formed . The diffusion of reacting species becomes facile with increased contact area of the B 2 O 3 and carbon components, enabling synthesis at a low temperature compared with the conventional carbothermal reduction process.…”