Oxidation kinetics of magnesium aluminum oxynitride-boron nitride (MgAlON-BN) composites

Abstract

The oxidation behaviour of MgAlON-BN composite was investigated under the air atmosphere using thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques in the present articles. Non-isothermal experimental results indicated that the rate of oxidation can be neglected at low temperature and, with further increasing temperatures, an increase of the oxidation was observed. While BN addition promoted the oxidation above 1100K, and the weight gain was observed to decrease due to the fast evaporation of boron oxide as the temperature was beyond 1580K. Isothermal studies also clearly indicated the decrease of weight gain due to evaporation after a certain oxidation time. The oxidation mechanism was investigated, and the results showed the oxidation products were γ-Al2O3at low temperature and transformed to α-Al2O3as the temperature was above 1100°C. BN addition promoted the transformation from γ-Al2O3to α-Al2O3. From the isothermal oxidations, the kinetics of oxidation and evaporation were evaluated, and the overall kinetics of oxidation and evaporation were studied, and the activation energy for evaporation of B2O3and for the oxidation of MgAlON-15 vol%BN at the later stage are 115.4 and 196.1 kJ/mol, respectively. The present paper provides a way to deal with oxidation of composites containing evaporating component.