HYDROGEN ABSORPTION AND IRON PASSIVE FILM BREAKDOWN IN ALKALINE ENVIRONMENTS

点击翻译按钮获取中文摘要

By using the scanning vibrating electrode technique, hydrogen permeation technique and polarization technique, the relation between the breakdown of the iron passive film and hydrogen absorption was investigated in mainly alkaline solutions containing H_2S and CO_2. Through two years'project, the following results were obtained :(1) In alkaline solution carbon steel showed no hydrogen absorption. However the abrupt increase in hydrogen absorption took place after a certain induction time by the addition of KCN,corresponding to the sudden decrease in corrosion potential. It was considered that KCN led to the breakdown of the iron sulfide film to expose bare surface.(2) In alkaline solution without CO_2, little hydrogen absorption was detected. On the other hand, the existence of CO_2 in the solution led largely to the increase in hydrogen absorption. This was explained in terms of the formation of iron carbonate film and the dissolution of the film.(3) Surface morphology was observed using the scanning vibrating electrode. Under the H_2S environment anodic part localized moved with time, whereas the anodic part under the CO_2 environment appeared to be uniformly distributed over the whole area.It was found that the surface morphology was different at both environments.(4) In general, it has been considered that the alkaline environments do not lead to the hydrogen absorption into materials. However, the present results showed that hydrogen embrittlement was possible to take place in alkaline environments with (H_2S+KCN) and CO_2.