Combustion Synthesis of Boron Nitride via Magnesium Reduction Under Low Nitrogen Pressures

Abstract

A combustion synthesis process was developed for the synthesis of h‐BN powder. B2O3, Mg, NH4Cl, and NaN3 were used as the reactants and they were mixed and pressed into a reactant compact, which was then wrapped up with an igniting agent (i.e., a mixed powder of Mg and Fe2O3). With the presence of NH4Cl and NaN3 in the reactant compact and the wrapping of the igniting agent, the combustion synthesis reaction could be carried out under low N2 pressures (<1.0 MPa) with high product yields (up to 79%) and high specific surface areas (SSA) of the product powder (up to 151 m2/g). Effects of process parameters on the product yield, SSA, and combustion temperature were investigated and a reaction mechanism was proposed to explain the effects. The synthesized h‐BN was platelike crystals and their SSA was found to increase with decreasing maximum combustion temperature under most of the experimental conditions. This is explained by the growth time of the crystals, which is considered to be shorter under the condition with a lower maximum combustion temperature.