Diffusion of Tritium in Cold‐Worked Palladium

Abstract

The mobility of hydrogen in cold-rolled palladium specimens of different degree of plastic deformation was measured by employing the tritium tracer method. -In one set of experiments the temperature dependence of the diffusivity was determined at very low hydrogen to metal ratios below aboutIn another set of experiments the influence of precharged hydrogen on the tritium mobility was investigated at constant temperature. -The diffusion of tritium as a tracer in presence of hydrogen and within an imperfect lattice is treated on the assumption of local isotope distribution equilibrium between traps and interstitial sites. A trap binding energy of about 18 kJmol-' is obtained. -By means of a selfconsistent evaluation of the experimental data also the trap binding entropy, the concentration of traps, and the separation factor of the isotope distribution equilibrium is determined. -It is found that tritium is enriched in interstitial positions. The concentration of traps is doubled on going from 30% to 50% of deformation. The localized vibrations of tritium in trap sites are found to be distinctly softer than in interstitial positionb. -We suggest dislocation cores and sites close to dislocation cores as operating traps. The interaction energy between hydrogen and dislocation traps is discussed in connection with the misfit energy of hydrogen in metals.

Artificial neural network-based path integral simulations of hydrogen isotope diffusion in palladium

“…In the experiment reported by Higelin et al [66], D became larger at temperatures below 75 K when the mass of H isotopes decreased. On the contrary, the quantum-TST-based D values, which were overall in good agreement with experimental values [64][65][66][67], did not clearly follow this trend. It is noted that those obtained from the DFT-based PIMD calculations in the previous study [22] agreed better with experimental values than the present MLP-based results at low temperatures (below 75 K).…”

Electrical Contacts for n-Type Diamond

“…Krimmel et al [23], for instance, shows that tetrahedral sites have considerably higher energy. Trap sites, on the other hand, were shown to provide spacious, flat potential wells for hydrogen and, therefore, much lower vibrational frequencies [20,40,45]. The flatness of the bottom of the octahedral site is that minima would develop around the edge of the site which add together to give flat bottom of the potential well.…”

“…It has been reported that under the influence of hydrogen, sintering of finely dispersed Pd can occur even at temperatures as low as 330 K [19]. Furthermore, enhanced mechanical stress or cold working [20] applied to the β-phase of palladium hydride may also cause particle growth and can lead to an enhanced defect density such as dislocations in the precious metal [21][22][23][24]. This may result in pronounced hysteresis effects of the hydrogen adsorption/desorption isotherms or the kinetics of hydrogen storage and release [7,8,20].…”

“…Most of the detailed work on hydrogen dynamics for example [25][26][27][28][29][30][31][32][33], and the trapping of hydrogen on dislocations ( [20][21][22][23][24] and literature cited therein) in the Pd/H system and other metal/hydrogen systems was focused on pure and well defined material such as single crystals or other bulk specimens with well determined preconditioning. In the present study, we have extended these existing neutron measurements on the palladium/hydrogen system, to several specimens of palladium of different morphologies, surface areas and pretreatments.…”

Effect of dislocation trapping on deuterium diffusion in deformed, single-crystal Pd

“…The SANS measurements presented here are not sensitive to the trapping interaction at very low bulk solubility levels. Trap binding energies have also been inferred from tritium diffusion measurements in 30 and 50 pct cold-worked Pd by Sicking et al [18] A representative binding energy of 0.2 eV was found by these authors.…”