Effect of Additional Element on Hydrogen Absorption for Iron in Acidic and Neutral Sulfate Solutions

摘要

Effects of additional elements of Cr and Ni in iron on hydrogen absorption behavior have been investigated by means of conventional electrochemical hydrogen permeation test. Empirical transient curve of hydrogen permeation current density was agreed with theoretical one on the basis of Fick’s second law with a fixed hydrogen concentration at the hydrogen absorption surface, C _(0), at any time. The fact suggests quasi-equilibrium condition to the absorption-desorption reaction of hydrogen at the surface, and that correlation between C _(0) and hydrogen absorption rate. As an analytical result of the transient, a diffusion coefficient decreased with an increase in a content of additional elements, and the decrement was enhanced much more by Cr than by Ni. C _(0) was almost proportional to a square root of the cathodic current density at the hydrogen absorption surface for any specimens. The slope increased with an increase in a content of the additional elements, and the increment was enhanced much more by Cr than by Ni. There was a correlation between the slope and the diffusion coefficient, and the correlation suggested that the additional elements of Cr and Ni attract hydrogen. In addition, the attraction effect of Cr was much more than that of Ni. Under anodic potential region, the effect of additional element on C _(0) was not clearly obtained in the solution of pH 2, but it is found that C _(0) of the Cr-added steel was larger and that of the Ni-added steel was smaller than that of Fe in the solution of pH 6.