Papers by Keyword: Diffusion Enhancement

Abstract: Atomic diffusion in metals is invariably enhanced by dissolution of hydrogen, in some cases by many orders of magnitude. This is a consequence of the formation of superabundant vacancies (SAVs), one of the general properties of M-H systems. Some examples of H-induced enhancement of interdiffusion in alloys and a detailed investigation of self-diffusion in Nb hydride, NbHx, are described, together with accelerated atomic migration observed in electrodeposited metals, also a consequence of SAV formation in the electrodeposition process.

Abstract: Self-diffusion coefficient of 95Nb in NbHx alloys (x=0.05,0.25 and 0.3) has been determined in the temperature range from 823 to 1323 K by using a serial sputter-microsectioning technique. The self-diffusion coefficient of Nb in the NbHx alloys are larger than that in Nb, suggesting that vacancies are formed by hydrogen dissolution, that is, the formation of hydrogen-induced vacancies. The value of the pre-exponential factor for the Nb diffusion in the NbH0.05 alloy is five times larger than that in Nb, while the difference in the activation energies between the NbH0.05 alloy and pure Nb is small. The self-diffusion enhancement in the NbH0.05 alloy is mainly caused by lowering in vibrational frequencies of atoms in the immediate neighborhood of hydrogen-induced vacancies.

Abstract: Diffusion in a metal under an elevated hydrogen pressure is interesting in view of the fact that the diffusion is enhanced owing to the injection of a large amount of vacancies into the metal. This is peculiar to an elevated hydrogen pressure because diffusion in a metal is generally suppressed under a hydrostatic pressure. In the present article, the effect of an elevated hydrogen pressure on interdiffusion and impurity diffusion is reviewed in the Au-Fe system which has a large difference in the hydrogen solubilities between g -Fe and Au under an elevated hydrogen pressure.