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Title: Microstructure of surface cerium hydride growth sites

Samples of cerium were exposed to hydrogen under controlled conditions causing cerium hydride sites to nucleate and grow on the surface. The hydriding rate was measured in situ, and the hydrides were characterised using secondary ion mass spectrometry, scanning electron microscopy, and optical microscopy. The results show that the hydriding rate proceeded more quickly than earlier studies. Characterisation confirmed that the hydrogen is confined to the sites. The morphology of the hydrides was confirmed to be oblate, and stressed material was observed surrounding the hydride, in a number of cases lathlike features were observed surrounding the hydride sites laterally with cracking in the surface oxide above them. It is proposed that during growth the increased lattice parameter of the CeH{sub 2} induces a lateral compressive stress around the hydride, which relieves by the ca. 16% volume collapse of the γ-Ce to α-Ce pressure induced phase transition. Cracking of the surface oxide above the laths reduces the diffusion barrier to hydrogen reaching the metal/oxide interface surrounding the hydride site and contributes to the anisotropic growth of the hydrides.
Authors:
 [1] ; ;  [2] ;  [3]
  1. Atomic Weapons Establishment, Aldermaston, Berkshire, RG7 4PR, United Kingdom and The School of Materials, University of Manchester, Manchester, M13 9PL (United Kingdom)
  2. Atomic Weapons Establishment, Aldermaston, Berkshire, RG7 4PR (United Kingdom)
  3. The School of Materials, University of Manchester, Manchester, M13 9PL (United Kingdom)
Publication Date:
OSTI Identifier:
22258628
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 32; Journal Issue: 3; Other Information: (c) 2014 Crown; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; CERIUM; CERIUM HYDRIDES; CRACKING; DIFFUSION BARRIERS; HYDRIDATION; HYDROGEN; LATTICE PARAMETERS; MASS SPECTROSCOPY; MICROSTRUCTURE; MORPHOLOGY; OPTICAL MICROSCOPY; OXIDES; PHASE TRANSFORMATIONS; SCANNING ELECTRON MICROSCOPY; STRESSES; SURFACES