Microstructure of Cr2O3 Scales Grown in Ar-5H2O-(5H2) at 850 °C.

Model alloy, Fe-20Cr (wt%), was oxidized in two gas mixtures Ar-5H2O-(5H2) (vol%) at 850 °C. The alloy formed Cr2O3 scales in both gases. The Cr2O3 scale developed faster in Ar-5H2O-5H2 and contained fine pores, whilst that grown in Ar-5H2O was dense. Experiments with inert SiO2 marker revealed that the Cr2O3 scale growth in Ar-5H2O-(5H2) was controlled mainly by outward Cr diffusion. When adjusted for grain boundary diffusion effects, Wagner's theory was successful in describing the hydrogen effect, provided that the Cr2O3 scales are n-type. [ABSTRACT FROM AUTHOR]