Surface reaction of polycrystalline Fe₃Si alloys with oxygen and water vapor

The surface reaction of polycrystalline Fe₃Si alloy with oxygen and water vapor was studied by means of Auger electron spectrum (AES) and X-ray photo-electron spectroscopy (XPS). The results showed that the oxygen and water vapor were first absorbed on the surface of specimen, then they preferentially reacted with the alloy constituent of Si to form SiO₂. At room temperature, both the molecular absorption and dissociated absorption of water vapor as well as oxygen occurred, but of the molecular absorption was relatively larger. Increasing temperature from 20 to 200°C deferred the surface reaction. The surface reaction of forming SiO₂ at room temperature was stoichiometry sensitive. Based on the study of on the surface reaction, this investigation predicts that the Fe₃Si alloys are prone to environmental embrittlement in water vapor and that the severity of environmental embrittlement may be stoichiometry sensitive.