Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2.

Transition metal silicides represented by MoSi₂have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi₂oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi₂at temperatures of 1000 °C-1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi₂underwent high-temperature selective oxidation reactions at 1000 °C-1200 °C, forming MoO₂and SiO₂oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO₂and the phase transformation of SiO₂, a continuous Mo₅Si₃layer with a thickness of approximately 47μm was formed at the SiO₂-MoSi₂interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO₂and Mo₅Si₃) during high-temperature oxidation process of MoSi₂. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo₅Si₃layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi₂coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo₅Si₃during the high-temperature oxidation of MoSi₂coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.