Interactions of water vapor with polycrystalline uranium surfaces - The low temperature regime

E. Tiferet, S. Zalkind, M. H. Mintz, I. Jacob, N. Shamir

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7 Scopus citations

Abstract

The initial interaction of water vapor with polycrystalline uranium surfaces at low temperatures (LT, 200 K), was studied by combined measurements utilizing Direct Recoil Spectrometry (DRS), Auger electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Three stages of water dissociation and adsorption can be observed: Stage (1) 0-0.6 oxygen monolayer coverage: full (H2O → O + 2H) dissociation is dominant, coexisting with partial dissociation (H2O → OH + H). In contrast to room temperature, where the adsorption is of a Langmuir type, in the present low temperature case it is a precursor-state type - the oxygen accumulation is linear, indicating that a constant fraction of the water molecules impinging on the surface diffuses to a dissociation and adsorption site. Only minor oxidation of the uranium occurs. Stage (2) 0.6-full oxygen coverage: only partial dissociation occurs. Still only minor oxidation of uranium takes place. Stage (3) buildup of a second hydroxyl layer, concurrent with slow continuous oxidation of uranium. Subsequent heating of the sample after the described exposure was accompanied by additional continuous oxidation. Above ∼230 K, the main process seems to be OH decomposition and desorption. A comparison is made to the dissociation and adsorption processes at room temperature.

Original languageEnglish
Pages (from-to)936-940
Number of pages5
JournalSurface Science
Volume601
Issue number4
DOIs
StatePublished - 15 Feb 2007

Keywords

  • Adsorption kinetics
  • Bilayer
  • Ion scattering spectroscopy
  • Oxidation
  • Uranium
  • Water
  • X-ray photoelectron spectroscopy

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