Role of boron carbide in carbothermic formation of hexagonal boron nitride

Abstract

Formation of hexagonal boron nitride by carbothermic reduction of boric oxide under nitrogen atmosphere at 1500 °C was investigated. Experiments were performed for durations in the range of 15 min to 3 h. Reaction products were subjected to powder X-ray diffraction analysis, chemical analysis and were examined by scanning electron microscope. Formation of hexagonal boron nitride was found to be complete in 3 h with most forming in the initial 2 h. Boron carbide was found to exist in the reaction products of the experiments in which hexagonal boron nitride formation was not complete. The aim of this study was to investigate the role of boron carbide in the carbothermic production of hexagonal boron nitride. For this purpose, conversion reaction of boron carbide into hexagonal boron nitride was studied. Boron carbide used in these experiments was produced in the same conditions that hexagonal boron nitride was formed, but under argon atmosphere. It was found that formation of hexagonal boron nitride from boron carbide—boric oxide mixtures was slower than activated carbon—boric oxide mixtures. It was concluded that boron carbide is not a necessary intermediate product in the carbothermic production of hexagonal boron nitride.