Decontamination of metal surface by reactive cold plasma: removal of cobalt

Recently plasma surface-cleaning or surface-etching techniques have been focused in the respect of decontamination of spent or used nuclear parts and equipment. In this study decontamination rate of metallic cobalt surface was experimentally investigated via its surface etching rate with a CF4-O2 mixed gas plasma. Experimental results revealed that a mixed etchant gas with about 80% CF4-20% O2 gives the highest reaction rate and the rate reaches 0.06 μm/min at 380degC. It was also found that ion-assisted etching lowers the reaction initiation temperature and substantially raises the surface etching rate. With a negative 300 DC bias voltage applied to the substrate, the reaction began to take place even at 290degC and its rate soared up to 0.43 μm/min at 380degC. Surface morphology changes before and after the reaction confirmed these etching rate measurements. Based on the current experimental findings and surface atoms analysis, fluoro-carbonylation reaction mechanism is proposed for the current metal surface etching system. (author)