Oxidation behaviour of a MoSi2-based composite in different atmospheres in the low temperature range (400-550 degrees C)

The oxidation characteristics of a MoSi2-based composite within the temperature range of 400-550 degreesC were investigated. The effects of temperature and water vapour on oxidation were examined. The oxidation kinetics were studied using a thermobalance, while the morphology and composition of the oxides were examined using XRD, ESEM/EDX, and SEM/EDX. The peak oxidation rates in dry O-2 and O-2 + 10% H2O were found to occur at temperatures of approximately 5 10 and 470 degreesC, respectively. Within the temperature range of accelerated oxidation (400-500 degreesC), the oxidation rate in O-2 + 10% H2O was substantially higher than that in dry O-2. At higher temperatures, the oxidation rate decreased, and the magnitude of the decrease was steeper and occurred at a lower temperature for O-2 + 10% H2O (510 degreesC) than for O-2 (550 degreesC). Furthermore, the rate of depletion of molybdenum (Mo) from the oxide scales during oxidation increased with increasing temperature and water vapour content. It appears that Mo loss is a key process influencing the protective properties of the oxide layer on the MoSi2 composite. A potential mechanism for the different oxidation behaviours in O-2 and O-2 + 10% H2O is proposed. (C) 2004 Elsevier Ltd. All rights reserved.