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https://hdl.handle.net/2142/71797
Description
Title
Hydrogen Transport in and Through Niobium
Author(s)
Sherman, Robert
Issue Date
1982
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
Two separate experiments were performed in order to understand the roles of bulk diffusion and surface processes in hydrogen transport in and through niobium. Bulk hydrogen and deuterium diffusivities and permeabilities were measured at high temperatures (700 - 1400 K) using diffusion controlled permeation methods. At lower temperatures, surface controlled permeation was used to investigate the role of the surface in hydrogen absorption and desorption.
In the high temperature hydrogen permeation experiments, diffusivities and permeabilities were measured from 700 K to about 1400 K at hydrogen pressures ranging from 4.26 Pa to about 0.013 Pa. The measured diffusivities are in agreement with values extrapolated from the low temperature surface independent measurements. In contrast to low temperature measurements, a trend indicating a classical isotope effect is observed for hydrogen and deuterium diffusivities in niobium at the higher temperatures. The measured hydrogen permeation constants agree with independent solubility and diffusivity measurements and are characterized by a negative enthalpy, as expected from low temperature solubility and diffusivity measurements. These results are contrasted with previous measurements which appear to have been controlled by surface reactions.
The surface controlled permeation experiments were in two parts, the adsorption experiments and the desorption experiments. In these experiments, the experimental conditions were arranged so that the reaction at the desired surface is the rate controlling step; this permitted the study of the kinetics of hydrogen passage through that surface.
As part of this work, we developed a method to electrochemically form Pd-black on Nb surfaces to insure barrier-free entrance and exit for H in Nb. The results for as-prepared "clean" surfaces and with O(,2), N(,2), Cl, CO, SO(,2) and H(,2)S input gases adsorbed on the surface will be discussed to investigate the effect of adsorbed species on surface permeation processes. The role of Ar('+) sputtering to clean and maintain a known surface chemistry will be discussed.
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