Surface oxidation of Zircaloy-4 at 600 K by adsorbed oxygen, nitric oxide, and sulfur dioxide

Understanding and controlling the formation of surface oxides on Zircaloy-4 (Zry-4) surfaces in the presence of nitrogen or sulfur at high temperatures is of interest in applications where this alloy serves as a structural material. In this article we monitor the adsorption of gases on Zry-4 surfaces at 600 K using Auger electron spectroscopy. We find that sulfur dioxide (SO2), nitric oxide (NO), and isotopic oxygen (18O2) all result in the formation of surface oxides. The presence of sulfur on the surface is reflected both in an increase in the intensity of the overlapping [Zr(MNV) + S(LMM)] feature and its shift toward higher kinetic energies. On the other hand, since oxide formation results in shifts of the Zr(MNV) Auger transition toward lower energies, opposite to what the presence of sulfur does, we also obtain useful information from the Zr(MNN) transition. Although exposure to oxygen results in the largest oxygen concentration near the surface, all the three adsorbates shift the Zr(MNN) feature by about 1.5–2.0 eV, indicative of surface oxidation.