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

用库仑滴定法测定了Fe-Cr-Al耐热合金(Cr22%，Al5%，Fe63%，俗称“Kanthal合金”)管材中氢的渗透量。即使没有任何处理，测得的磁导率约为普通耐热Fe-Cr合金磁导率的千分之一。测定值与金属管材上形成的氧化层厚度相容的氧化铝陶瓷的测定值基本一致，说明Fe-Cr-Al合金管材的氢渗透是由管材表面形成的氧化铝层控制的。研究了在Fe-Cr-Al管材表面形成的氧化膜上建立的电动势及其极化效应，以探讨阴极保护氢渗透的可能性。由电动势测量证实，由于…的化学极化效应，合金衬底上的氢势保持在较高的值我们已经指出了更多。然而，阴极极化对氢渗透的影响尚不清楚，因为在还原条件下极化使氧化膜变得不稳定，而且渗透速率自然处于很低的值。因此，采用内外多孔铂电极氧化铝陶瓷管材来代替金属管材表面形成的氧化膜，并详细研究了极化对样品的影响，证实了极化条件的改变会使氢气从氧化铝块体中掺入或释放出来。通过计算极化样品中的氢化学势分布，对这一现象进行了分析。在此基础上，测定了氢气在工业多晶氧化铝中的溶解度。在1573K下施加0.8V的阴极极化一段时间后，观察到通过氧化铝管的渗透被完全阻止。因此，如果在金属管表面形成稳定的掺杂二价元素的氧化铝薄膜，就有可能对金属管的氢渗透进行阴极保护。在研究过程中，观察到了金属氧化初期氢的异常掺入、氢在氧化铝中的过饱和以及与氢/质子电极反应有关的新机理。在本研究的子工作中也给出了对这些现象的可能解释。较少

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