Kinetics of MoSi2 pest during low-temperature oxidation

Abstract

The kinetics of MoSi₂ pest, caused by oxidation in air, has been studied. Experimental results indicated that pest disintegration occurred at temperatures between 375 and 500 °C. The volumes of test samples increased with oxidation duration. Analysis of change in sample volume versus oxidation duration revealed that the pest disintegration consisted of two stages, namely nucleation (or incubation) and growth. The onset of the growth stage depended on the test temperature. More importantly, changes in sample volume were found to obey a linear relationship with time during the growth stage. Equations were formulated to demonstrate that the growth kinetics of pest disintegration was proportional to the rates of change in sample volume. The rates of volume change during MoSi₂ pest were calculated to be 4.9 × 10⁻⁶, 2.8 × 10⁻⁵, 3.7 × 10⁻⁵, and 5.4 × 10⁻⁵ cm³/s at 375, 400, 425, and 450 °C, respectively; the growth kinetics increased with oxidation temperature. The activation energy for the growth stage of pest disintegration was determined to be 27.6 kcal/mole, which agrees well with the activation energy for the low-temperature oxidation of MoSi₂.