Synthesis of highly purified and crystallized h‐BN using calcium‐assisted carbothermal reduction nitridation

Abstract Highly purified and crystallized hexagonal boron nitride (h‐BN) powder is suitable as thermally conductive filler in resins. To obtain h‐BN powder with large particle size, as well as high purity and crystallinity, high‐temperature heat treatment over 1800°C in a N ₂ gas atmosphere is effective. The carbothermal reduction nitridation (CRN) involves the carbothermic reduction of boric oxide in a N ₂ gas atmosphere. In CRN using a CaO promoter, h‐BN particles with high crystallinity can be obtained by a simple heat treatment process. CaO prevents the evaporation of boron oxide and aids in h‐BN particle growth at high temperatures. However, CaB ₆ is formed as byproduct or impurity when CRN using the CaO promoter is performed at temperatures higher than 1800°C. In this study, the relationship between the products and the reaction temperature was clarified via thermodynamic considerations and experimentation. The results clarified the ideal reaction process of CRN using a CaO promoter to obtain highly purified and crystallized h‐BN powder.