Oxidation of Zircaloy-4 by H2O followed by molecular desorption

The interaction of H2O with Zircaloy-4 (Zry-4) is investigated using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) methods. Following adsorption of H2O at 150 K the Zr(MNV) and Zr(MNN) Auger features shift by 6.5 and 4.5 eV, respectively, indicating surface oxidation. Heating H2O/Zry-4 results in molecular desorption of water at both low and high temperatures. The low-temperature desorption is attributed to ice multilayers, whereas, three overlapping high-temperature features are presumably due to recombinative desorption. This high-temperature desorption begins before the surface oxide is dissolved, continues upon its removal, and is atypical for water/metal systems. Unexpectedly, no significant desorption of hydrogen is observed near 400 K, as is typically observed following O2 adsorption on Zr-based materials. However, we do observe that H2O adsorption on Zry-4 surfaces roughened by argon ion sputtering results in H2 desorption.