Heat Induced Surface Modifications Affecting Initial Hydriding Kinetics in Uranium*

Bloch, J.; Swissa, E.; Mintz, M.H.

doi:10.1524/zpch.1989.164.part_2.1193

Cited by 23 publications

(16 citation statements)

References 4 publications

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“…reaction initiates at discrete sites on the surface of the metal, the number and distribution of which have been observed to vary with surface preparation, grain size, purity, and inclusion size and distribution, among other variables. [4,5,6] The kinetics do vary considerably with the metallurgical condition of the specimen, which effect has been attributed to variations in the nucleation kinetics. [7] previous published studies of the site selection of hydrogen attack on uranium: Owen and Scudmore [4] looked at "pure" U.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Surface Morphology and Oxide Microstructure on the Nucleation and Growth of Uranium Hydride on Alpha Uranium

1998

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While the bulk kinetics of the uranium-hydrogen reaction are well understood, the mechanisms underlying the initial nucleation of uranium hydride on uranium remain controversial. In this study we have employed environmental cell optical microscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy, (AFM) in an attempt to relate the structure of the surface and the microstructure of the substrate with the susceptibility and site of hydride nucleation. Samples have been investigated with varying grain size, inclusion (carbide) concentration, and thermal history. There is a clear correlation to heat treatment immediately prior to hydrogen exposure. Susceptibility to hydride formation also appears to be related to impurities in the uranium. The oxidized surface is very complex, exhibiting wide variations in thickness and topography between samples, between grains in the same sample, and within individual grains. It is, however, very difficult to relate this fine scale variability to the relatively sparse hydride initiation sites. Therefore, the surface oxide layer itself does not appear to control the sites where hydride attack is initiated, although it must play a role in the induction period prior to hydride initiation.

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Section: Introductionmentioning

confidence: 99%

The Influence of Surface Morphology and Oxide Microstructure on the Nucleation and Growth of Uranium Hydride on Alpha Uranium

1998

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“…Prior to each hydriding experiment the sample was heated under vacuum up to 920 K. It is well known that heating the sample in vacuo may drastically reduce the incubation times due to a degassing activation effect attributed mainly to H 2 O or hydroxyls desorption process [8,4]. Preliminary experiments pointed out that temperature of 920 K is optimal for the vacuum pretreatment of Ho bulk samples regarding reproducibility and reliability of the experimental results.…”

Section: Resultsmentioning

confidence: 99%

The hydriding kinetics of bulk metallic holmium under 1bar H2 and below 570K

Bloch¹

2008

Journal of Alloys and Compounds

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“…Appearance of an induction period is widely attributed to slow diffusion of hydrogen through the PuO 2 layer on Pu surfaces [3,[6][7][8][9]. Accumulation of hydrogen at the oxide metal interface then results in localized hydriding that expands and ruptures the overlying oxide.…”

Section: Introductionmentioning

confidence: 99%