Dissolution kinetics of metal coating in HNO3-scCO2 micro-emulsion using QCM

Radioactive contamination is rising because of an increasing number of nuclear facilities. Among the decontamination methods, the surface decontamination method is especially important. Conventional chemical decontamination methods for surface decontamination cause not only secondary radioactive wastes, but also corrosion and defects on the surface of equipment. Therefore, we require a new surface decontamination method. If CO2 is used as a solvent for decontamination of radioactive contaminants, the wastes can be effectively reduced by recycling the CO2. Supercritical fluid has many good points as a process solvent, including low viscosity, negligible surface tension, and variable selectivity. And supercritical fluids have physical properties of both liquid and gas, such as good penetration with a high dissolution capability. A number of workers applied supercritical CO2 solvent for cleaning precision devices and waste treatments. Since supercritical CO2 has its mild critical point at 31 .deg. C and 73.8bar as well as low surface tension, it is a potentially suitable cleaning substance. The operational costs of CO2 cleaning were estimated to be lower than other cleaning processes. However supercritical CO2 has limited solubility about contaminated material. To tackle these problem, we researched various aspects of surfactants. Quartz Crystal Microbalance (QCM) is a thickness-shear mode resonator in which the acoustic wave propagates in a direction perpendicular to the crystal surface. The use of QCM as a chemical sensor has its origins in the work of Sauerbrey and King who carried out micro-gravimetric measurements in the gas phase. It was assumed in their work that a thin film applied to a thickness-shear-mode device could be treated in sensor measurements, and a shift in the resonance frequency of an oscillating AT-cut crystal could be correlated quantitatively with a change in mass added to or removed from the surface of the device. Now, the QCM technique expands its application area to pressurized fluids such as liquids and supercritical CO2. In this study, we made a HNO3-scCO2 microemulsion to remove a film from a contaminated metal surface. F-AOT and Proline surfactant-1 were used as a surfactant. HNO3 was used as a acid solution for dissolution Cu coating. As a setting for experimental conditions, we analyzed the film removal characteristics of Cu and Ni coated QCM