How does the surface protective film on molybdenum disilicide components form under high-temperature oxidizing atmospheres?
2026-04-10
Molybdenum disilicide (MoSi₂) components, when exposed to high-temperature oxidizing atmospheres, form a protective surface film owing to their unique physicochemical properties.
Molybdenum disilicide (MoSi₂) components, under high-temperature oxidizing atmospheres, develop a protective surface film owing to their unique physicochemical properties. When the ambient temperature exceeds 1200°C, MoSi₂ reacts with oxygen, and the surface silicon atoms are preferentially oxidized to form silicon dioxide (SiO₂). In the initial stage, SiO₂ deposits as an amorphous glassy layer on the component’s surface; as the temperature rises or the oxidation time extends, this layer gradually densifies, ultimately forming a continuous protective barrier.
The key to this process lies in the self‑healing capability of the SiO₂ film: when microcracks develop in the film due to thermal stress, localized high temperatures cause the SiO₂ to melt and flow, automatically filling the cracks and restoring the film’s integrity. Moreover, SiO₂ remains chemically stable below 1800°C, effectively preventing oxidizing agents such as oxygen and water vapor from contacting the substrate material. It is worth noting that when the component surface temperature exceeds 1710°C—the melting point of SiO₂—the film temporarily loses its protective function as it melts and coalesces into droplets; however, once the temperature drops, a new SiO₂ layer reforms.
The crystallographic characteristics of molybdenum disilicide also underpin this protective mechanism: its tetragonal structure imparts metallic ductility above 1000°C, enabling plastic deformation to relieve thermal stresses and thereby reducing the risk of coating spallation. This dynamic equilibrium between oxidation and self‑healing ensures that molybdenum disilicide components maintain long-term stability in oxidizing atmospheres up to 1600°C.
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