Evaluation of Integrated Metal-Oxide Electrode Prepared Using Thermal Oxidation for Corrosion Monitoring in Nuclear Reactor

摘要

An yttria-stabilized-zirconia-(YSZ)-membrane metal-oxide (M/O) electrode was used as a reference electrode to measure the electrochemical corrosion potential of the material used to build the structures of reactors. The electrode can operate at high temperatures because of the conductivity of YSZ membrane tube. It also has a braze juncture between the YSZ membrane and metal tubes, which may corrode in high-temperature water. This corrosion should be prevented to improve the performance of the M/O electrode. An integrated Ni/NiO electrode was developed (i.e., integrated metal-oxide electrode, IMOE) to eliminate the braze juncture and increase the conductivity of YSZ. The reference electrode's performance is evaluated in this paper. The sputter-deposited thin films of the IMOE detached from the boundary between the Ni substrate and the NiO film in a buffer solution (pH 7) at room temperature. Thermal oxidation was then used to deposit a durable nickel-oxide film onto a Ni substrate in order to produce an improved IMOE. A multilayered improved IMOE structure lasted up to 1100 hours during an immersion test. The potential of the improved IMOE is more stable than that of the former IMOE and has a drift of 0.01-0.1 mV/h. The improved IMOE also exhibited a pH response in buffer solutions (pH 4.02-9.26) at room temperature. The pH response has a slope of -56.9 mV/pH, which is 4% smaller than the ideal pH response (-59 mV/pH). Thermal oxidation was effective at improving the durability and pH response of the IMOE at room temperature.