The effect of S, N, and C on the oxidation of Ni-20%Cr and Fe-20%Cr

The effect of S, N, and C on the oxidation of Ni 20%Cr and Fe-20%Cr was investigated by two approaches (i) using AES and LEED following oxide nucleation and growth under UHV conditions and (ii) by thermogravimetry and subsequent SEM analysis, under conditions where only adsorption/segregation of these elements and congregation of Cr occurred. Sulfur retards nucleation, inhibits lateral growth, and leads to a coarse-grained oxide with a wide network of ridges at the grain boundaries—the growth rate decreases with increasing sulfur activity. Nitrogen and carbon or rather the cosegregated Cr promote the nucleation of C2O3, which leads to many grains and grain boundaries in the oxide layer, accelerated growth and a sponge-like morphology.