Abstract A model Si-free alloy, Fe-30Cr (wt.%), was exposed to Ar-10H 2 O mixture (in vol.%) at 650 °C, forming a protective Cr 3 scale, which contained silica. Liquid water used form vapour in bubbler either deionised or distilled. In both cases, low-level impurities of Si, F, Cl, S, and Ca matched those detected the scales by TEM/EDX ToF–SIMS. Consideration droplet residual solute particle si...