Diffusion Coefficient of Hydrogen in Pure Iron between 230 and 300 K

Diffusion coefficient of hydrogen in iron has been determined at temperatures between 230 and 300 K. The permeation of hydrogen through the speimen has been measured by an electrochemical method in which alcoholic solutions were used as electrolytes. The experimental permeation curves were analyzed by considering the variation of the hydrogen concentration beneath the cathodic surface during the measurements. The diffusion coefficient of hydrogen thus obtained in a single crystalline specimen is given by D(m2⁄s)=1.1×10−7exp(−6700(J⁄mol)⁄RT) which agrees with high temperature values reported in the literature, but in a poly-crystalline specimen it is not expressed by a single Arrhenius equation. At 298 K, D is given by 7×10−9 m2/s, which is independent of the existence of grain boundaries and the specimen thickness.