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耐蚀性与其上形成的钝化膜的电子结构之间的关系。本研究主要针对钛合金的钝化膜进行研究。用光电化学方法研究了钛及含5AT%3d(V，Cr，Mn，Fe，Co，Ni，Cu)、4d(Nb，Mo)和5d(Ta)的钛及钛合金钝化膜的电子状态。此外，用分子轨道计算方法计算了钝化膜的电子结构。对钝化膜的电子结构进行了计算，并与实验结果进行了比较，发现每种合金的钝化膜在光照下都出现了正的光电流。这意味着钛合金的钝化膜具有n型半导体的特性。这些特性并不随合金元素的变化而变化。…测得的光电流谱的形状另外，通过改变入射光的波长也不会随着合金元素的变化而改变。测得钝化膜的带隙约为4.OeV。与此相反，表征能带弯曲程度的平带电势随合金元素的不同而变化很大。Co、Cu、Nb、Ta的加入降低了样品的平带电势，而Fe、Mo的加入提高了样品的平带电势。研究发现，合金钝化所需的电流密度与合金的平带电位有很好的相关性，该电流密度是衡量合金耐蚀性的一个指标。平带电位较低的合金钝化电流密度较小。钝化膜的带隙计算值与实验值吻合较好。然而，平带势能与计算的费米能级之间没有明显的关系，预计费米能级是导致能带弯曲的原因。在这方面，有必要进行进一步的理论考虑。较少

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