P-5 超音波照射下における純チタンのカソード分極特性
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概要
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Titanium is one of the prominent candidate for the material of an overpack for the geological disposal of high-level radioactive wastes. After being enclosed the radioactive wastes, the overpack is disposed of in deep ground, where it is to contact with a reducing groundwater, which will be irradiated by γ -ray from the inside of it. The cathodic polarization behavior of a material is a key factor in controlling its corrosion rate in a reducing solution, and the polarization behavior of pure -titanium was investigated under ultrasonic irradiation, because where the solution is dissociated to hydrogen and hydroxyl radicals as well as under the γ -irradiation. The cathodic current was increased with the irradiation intensity. This current increasing was supposed to be provided by the reduction of hydrogen peroxides, which were generated by the union of hydroxyl radicals that had be formed by the ultrasonic irradiation; H_2O → ・H + ・OH, ・OH + ・OH → H_2O_2, H_2O_2 + 2e^- → 2OH^-. To confirm the supposed mechanism, the H_2O_2 concentrations in the solution were measured before and after a constant cathodic potential being applied to the pure-titanium electrode, evaluating the change in the H_2O_2 reduction rate. The results, however, showed only the about half of the cathodic current was provided by the reduction of the H_2O_2. Accounting this difference, we considered the possibility of the direct discharging from the hydroxyl radicals; ・OH + 2e^- → 2OH^-. If this mechanism hold, the increasing of the cathodic current is not restricted by the reduction rate of the H_2O_2, but the generation rate of H_2 is increased because the hydrogen radicals that do not recombine with the hydroxyl radicals form H_2 gas as follows; ・H + ・H → H_2. To confirm the supposed model, the H_2 generation rates were measured before and after the electrode being polarized, however, the generation rates were not changed with the polarization, so that it was considered that the model could not hold.
- 日本ソノケミストリー学会の論文