Effect of Water-Vapor Content on Reaction Rate of Hexagonal BN Powder at 1273 K

Abstract Hexagonal BN powder with average particle size of 1.2 µm was exposed at 1273 K in H ₂ O/air gas mixture with the range of mass ratio from 0:100 to 6.5:100 at a total pressure of 1 atm. Thermalgravimetry (TG) method was used to measure the reaction behavior of BN powder in water vapor. XRD and SEM were employed to analyze the phases and morphological revolution during reaction. The TG curves showed that the overall reaction process could be divided into two stages. In first stage, weight gained rapidly and the main reaction was the oxidation of BN. The weight gain turning point of the curves with different water-vapor contents varied, indicating that water-vapor had an impact on oxidation rate to some degree. In second stage, weight loss due to B ₂ O ₃ reacting with H ₂ O to form volatile product. The rate of weight loss increased with increasing the water vapor content. The reaction rate was described by a linear rate law, i.e., α = − k _l t . The relationship between k _l and partial pressure of water vapor p was described by a function of k _l = 0.4 p . The determination of the activation energy was complicated due to variations in the reaction mechanism.