The relative amount of trapped hydrogen and the activation energy for its evolution from various lattice defects in iron were calculated by monitoring the pressure change caused by release of hydrogen from charged specimens heated at uniform heating rates. Hydrogen release peaks were observed at 385 K, 488 K, and 578 K, respectively, when the hydrogen charged specimen were heated at 2.6 K per minute. Analysis suggests that the peak at 385 K corresponds to hydrogen release from grain boundaries, and the peak at 488 K corresponds to release from dislocations, while the peak at 578 K results from release from micro voids. The activation energies for evolution of trapped hydrogen were determined experimentally from measured peak temperatures at different heating rates and were found to be 17.2 KJ/mol, 26.8 KJ/mol, and 35.2 KJ/mol, respectively, in grain boundaries, dislocations, and microvoids. It was also observed that most of hydrogen is trapped on dislocations if the density of specimen is greater than 98.95 pct, and in microvoids if less than 98.95 pct.

Stationary and non-stationary states of flow of hydrogen in palladium and iron

Thermal analysis of trapped hydrogen in pure iron

The solubility and diffusivity of hydrogen in well-annealed and deformed iron

Diffusion of hydrogen in metals

Electrochemical methods for the investigation of metal-hydro gen systems are superior to other techniques, e.g., gas-volumetric, because of their simple procedure and their flexibility towards variation of experimental conditions. Moreover, these techniques allow measurements at very low hydrogen equilibrium pressures which occur, for instance, in the V(a)-metal-hydrogen systems in the concentration range of ideal dilute solutions at normal temperatures.

The removal of surface layers, which retard the hydrogen passage from the electrolyte into the metal and vice versa, is a necessary condition for electrochemical methods to be applicable. Using ultra-high-vacuum techniques, surface hindrances on base metals like V, Nb, Ta, Ti, and others, can be eliminated. Thus, it is possible to study diffusion, permeation, and solubility of hydrogen (isotopes), in these metals as well as in precious metals such as palladium and its alloys.

Various electrochemical hydrogen-diffusion and permeation methods are presented and compared. Their applicability and the limits of application are demonstrated for pre-selected systems.

A recently developed electrochemical technique for measuring hydrogen (isotope) solubility in transition metals is described. By means of this method, pressure-concentration equilibrium isotherms of V, Nb, and TaH systems have been obtained recently, at ordinary temperatures, from vanishingly low hydrogen concentrations, corresponding to extremely low equilibrium pressures, up to atomic ratios H/Me of 0.5.

Electrochemical methods for studying diffusion, permeation and solubility of hydrogen in metals

Diffusion rates F (cm3 STP/cm2 min) of hydrogen from the upstream pressure P (atm) into vacuum through a palladium sheet of thickness L (microns) are represented by logF=3.70+0.68 logP−623/T−logL, except for very thin membranes. Explanations are suggested for the wide discordance of earlier results in the study of the diffusion of hydrogen through palladium.

Stationary and non-stationary states of flow of hydrogen in palladium and iron

Citations

Thermal analysis of trapped hydrogen in pure iron

The solubility and diffusivity of hydrogen in well-annealed and deformed iron

Diffusion of hydrogen in metals

Electrochemical methods for studying diffusion, permeation and solubility of hydrogen in metals

Diffusion of Hydrogen through Palladium

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