Effect of Volatile Species on Chemical Vapour Deposition of SiO2 During Corrosion of Chromia- and Alumina-Formers

Silicon-bearing vapour at low pressure was used to deposit SiO2 during exposure of pure chromium, Fe-30Cr (wt.%) and Kanthal APM alloy to an Ar-10H2O-0.1HCl mixture (vol.%) at 650 °C. Pure Cr formed porous chromia blades on top of a polycrystalline Cr2O3 scale containing SiO2. A model Fe-30Cr alloy formed a scale consisting of a thick, amorphous (Cr,Si)Ox outer layer and a thin, polycrystalline Cr2O3 inner layer. Kanthal alloy formed a thin scale containing a Si-rich oxide outer layer and an inner layer of Fe, Cr, and Al oxides. Amorphous (Cr,Si)Ox nodules formed locally on top of (Cr,Fe)23C6 precipitates at the Kanthal surface.