The role of electronic structures of passive film in corrosion resistance of transition-metal based alloys

本研究的目的是阐明过渡金属基合金的耐蚀性与在其上形成钝化膜的电子结构之间的关系。在本研究中，重点研究了钛合金的钝化膜。采用光电化学技术对含5at% 3d （V、Cr、Mn、Fe、Co、Ni、Cu）、4d （Nb、Mo）和5d （Ta）的Ti和Ti合金钝化膜的电子态进行了研究。此外，采用分子轨道计算方法计算了钝化膜的电子结构。对钝化膜电子结构的计算结果与实验结果进行了比较。将各合金的钝化膜暴露于光下，观察到正光电流。这意味着钛合金的钝化膜具有n型半导体的特性。这种特性不随合金元素的变化而变化。通过改变入射光波长得到的光电流谱的形状也不随合金元素的变化而变化。测得的钝化膜带隙约为4。”项目。与上述事实相反，代表能带弯曲程度的平带势在很大程度上取决于合金元素。Co、Cu、Nb和Ta的加入使合金的平带电位降低，而Fe和Mo的加入使合金的平带电位升高。合金钝化所需的电流密度是衡量合金耐蚀性的一个指标，与合金的平带电位密切相关。平带电位较低的合金具有较小的钝化电流密度。钝化膜带隙的计算值与实验值吻合较好。然而，平带势与计算出的导致能带弯曲的费米能级之间没有明显的关系。在这方面需要进一步的理论审议。少

The purpose of this study is to clarify the relations between corrosion resistance of transition-metal based alloys and electronic structures of passive films formed on them. In this study, attention was focused on the passive films of Ti alloys. The electronic states of passive films were examined for Ti and Ti alloys containing 5at% of 3d (V,Cr, Mn, Fe, Co, Ni, and Cu), 4d (Nb and Mo) and 5d (Ta) with the photoelectrochemical technique. In addition, the electronic structures of passive films were calculated by using the molecular orbital calculation method. The calculation results on the electronic structures of passive films were compared with the experimental results.The positive photocurrent was observed when the passive film of each alloy was exposed to the light. This means that the passive films of Ti alloys have the characteristics of n-type semi-conductor. Such characteristics did not change in accordance with the alloying elements. The shape of photocurrent spectra obtained … More by changing the wave-length of incident light also did not change in accordance with alloying elements. The measured band-gap of passive films was about 4. OeV.In contrast to the above fact, the flat-band potential which represents the degree of band bending changed largely depending on the alloying elements. The flat-band potential decreased by the addition of Co, Cu, Nb and Ta, whereas it increased by the addition of Fe and Mo. It was found that the current density necessary for the passivation of alloy, which is a measure of the corrosion resistance of alloy, was well related to the flat-band potential of alloy. The alloy with less-noble flat-band potential has a small current density for the passivation. The values of calculated band-gap of the passive films were in good agreement with those obtained in the experiments. However, there was no obvious relation between the flat-band potential and the calculated Fermi energy level which was expected to be responsible for the band-bending. Further theoretical consideration would be necessary in this regard. Less