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https://hdl.handle.net/2142/25406
Description
Title
Hydrogen transport in and through niobium
Author(s)
Sherman, Robert
Issue Date
1982
Doctoral Committee Chair(s)
Birnbaum, Howard K.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
hydrogen transport
niobium
bulk diffusion
Language
en
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 is 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 temterature measurements, a trend indicating a classical isotope effect is observed for hydrogen and deuterium diffusivities in niobium at the higher temperatures. The measured hydrogen permeat ion constants agree with independent sol utility 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 t the adsorption experiments and the desorption experiments. In these experiments t the experimental conditions were arranged so that the reaction at the desired surface is the rate controling 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 Pdblack on Nb surfaces to insure barrier-free entrance and exit for H in Nb. The results for as-prepared ""clean"" surfaces and with ° 2 N2 Cl t COt S02 and H2S 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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