Journal of the Ceramic Society of Japan
Online ISSN : 1348-6535
Print ISSN : 1882-0743
ISSN-L : 1348-6535
Special Articles: The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Low-temperature synthesis of boride powders by controlling microstructure in precursor using organic compounds
Masaki KAKIAGE
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2018 年 126 巻 8 号 p. 602-608

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The carbothermal reduction of boron oxide (B2O3) is an important process for the synthesis of boride powders. As a low-temperature synthesis method for boron carbide (B4C) powder by carbothermal reduction, we focused on an approach using a condensed product prepared from boric acid (H3BO3) and an organic compound with a number of hydroxyl groups (a polyol) such as glycerin, mannitol, or poly(vinyl alcohol). A borate ester bond was formed by the dehydration condensation of H3BO3 and a polyol, leading to the homogeneous dispersion of the boron and carbon sources at the molecular level. The thermal decomposition of a condensed H3BO3-polyol product in air was performed to control the amount of carbon to the stoichiometric C/B2O3 ratio required for carbothermal reduction. Within the thermally decomposed product consisting of B2O3 and carbon components (B4C precursor), a B2O3/carbon structure at the nanometer scale was formed. The improved dispersibility and homogeneity of the B2O3/carbon microstructure accelerated the B4C formation at a lower temperature. Consequently, crystalline B4C powder with little free carbon was synthesized by heat treatment at a low temperature of 1200°C in an Ar flow. This low-temperature synthesis approach was applied to the low-temperature synthesis of other boride powders, i.e., boron nitride and calcium hexaboride powders.

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