Synchrotron X-Ray Reflectivity Study of Ni-Oxide-Passive-Layer-and-Water Interface and Yttrium-Stabilized-Zirconia-and-Water Interface

The hydration and water interaction at Ni-oxide-water interface and yttrium-stabilized-zirconia (YSZ)-water interface, respectively, have been investigated with synchrotron X-ray reflectivity. For the nickel-oxide-water interface, a thin passive oxide layer was grown on a single crystal Ni(110) substrate in ultra-high vacuum chamber by blowing in pure O₂ gas at room temperature after several cycles of sputtering-and-annealing treatment. The high-resolution specular X-ray reflectivity from the passive oxide layer as grown on the single crystal metal substrate was measured in He environment at room temperature to characterize the thin film thickness and the atomic correlations within the oxide thin film. The detailed interfacial structure and the substrate relaxation with a subatomic resolution could be derived based on the measured X-ray reflectivity in terms of the laterally averaged electron density profile in surface normal direction. The virgin passive oxide layer then exposed to pure water, the effect of hydration was observed with the subsequent reflectivity measurement at the same diffractometer geometry. The resultant X-ray reflectivity data showed drastic changes from the original reflectivity data, which indicates a substantial influence of water interaction on the surface termination of the passive layer. On the other hand, single crystal YSZ-water interfaces were studied as representing the most stable ZrO₂ phase and water interface system. The three major crystallographic orientations, (111), (110), and (100), were measured and analyzed for the interfacial hydration structures. The studies eventually aim at fundamental understanding of the water interaction on passive oxide layer of metal alloy surface in nuclear power plant environment. Before directly approaching to the simulated reaction in hot pressurized water, the current study provides the reference data to be compared to.