Development of the protecting method for hydrogen(and its isotopes) permeation through metallic pipes by cathodic polarization

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The permeation of hydrogen through the pipe made of Fe-Cr-Al heat-resisting alloy (Cr22%, Al5%, Fe63% usually called "Kanthal Alloy") was measured by coulometric titration method. Even without any pretreatments, the measured permeability coefficient was found about one thousandth of that of usual heat-resisting Fe-Cr alloy. The measured value was nearly equal with that of alumina ceramics of the compatible thickness with the oxide layer formed on the metallic pipe, which suggests that the hydrogen permeation through the Fe-Cr-Al alloy pipe is controlled by the alumina layer formed on the surface of the pipe.The electromotive force established across the oxide film formed on the surface of the Fe-Cr-Al pipe and its polarization effect were studied in order to examine the possibility of cathodic protection of the hydrogen permeation. By emf measurement the hydrogen potential in the alloy substrate was confirmed to be maintained at high value due to the chemical polarization effect which … More had been already pointed out by us. The effect of cathodic polarization on the hydrogen permeation, however, was not confirmed clearly because the oxide film was made unstable by polarization in the reducing condition and also the permeation rate was naturally at very low value. Therefore, the pipe of polycrystalline alumina ceramics with porous platinum electrodes on inner and outer sides were employed in the place of the oxide film formed on the surface of the metallic pipe and the effect of polarization on this sample was studied in detail.It was confirmed that hydrogen was incorporated or released from the bulk of alumina on the change of the polarization conditions. This phenomenon was analyzed by calculating the hydrogen chemical potential profile in the polarized specimen. Based on this analysis, the solubility of hydrogen into the commercial polycrystalline alumina was determined. After a period of cathodic polarization by imposing 0.8V at 1573 K, it was observed that the permeation through the alumina pipe was perfectly blocked. Therefore, the possibility of cathodic protection of hydrogen permeation of a metallic pipe was confirmed if the stable alumina film doped with bivalent elements was formed on the surface of the pipe.The new phenomena such as the extraordinary incorporation of hydrogen at initial stage of oxidation of the metal, the super saturation of hydrogen into alumina, and the new mechanism relating with the hydrogen/proton electrode reaction were observed in the course of this study. The possible explanations of these phenomena were also given in the sub works of this research. Less