固溶水素による鉄の格子膨張

Abstract

The strain due to dissolved hydrogen atoms in electrolytic iron was measured by two independent techniques; a measurement of change in the electrochemical hydrogen permeation rate with the application of elastic tensile stress, and a measurement of change in the length of a specimen as a function of hydrogen concentration.The hydrogen permeation rate increases with the application of stress but the diffusion coefficient of hydrogen is independent of stress, so that the stress application affects the solubility of hydrogen in iron. The logarithm of the ratio of the permeation rate in the stressed condition to that in the unstressed condition (ln(Jσ⁄J0)) is proportional to the applied stress (σ). The fractional increases of the permeation rate with increasing stress (ln(Jσ⁄J0)⁄σ) at ic=10−20 A/m2 are almost the same irrespective of the composition of the electrolyte.The strain of a unit cell of the iron lattice containing one hydrogen atom can be calculated from change in the permeation rate of hydrogen with the applied stress by using the equation ln(Jσ⁄J0)⁄σ=a3ε⁄kT, where a is the lattice parameter and ε is an average of the diagonal elements of the strain tensor. The value of ε is 0.057 (at T=296 K).The relative expansion of the iron specimen per atomic fraction of hydrogen dissolution corresponds to 2ε. The observed dilation of the iron specimen is the same within experimental error as that calculated from the above-mentioned value of ε and the hydrogen concentration.