1. General mechanisms

The general mechanisms of halogen corrosion are comparable to those of oxidation or sulfidation (cf. articles and ). However, due to the high volatility of the products, halide layers are generally not formed. Halogen attack then manifests itself as a combination of spalling of the oxide layers formed and internal or intergranular attack of the material, with, in particular, the formation of pores resulting from this high volatility. Alloy performance is dictated by halide properties: high saturation vapour pressure, high volatility, low melting points, differences in thermal expansion coefficients with the metal, and effects on the direction of reactions insofar as oxides and sulphides are thermodynamically favoured over halides. As with previous types of corrosion, metal-O-Cl stability diagrams can be used to predict possible corrosion products....