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Actinide surface chemistry.

Bishop, Alexander James. 2010. Actinide surface chemistry. PhD Thesis, Cardiff University.

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Abstract

The surface reactivity of thorium and uranium, and how this links to the 5f electrons, has been investigated under UHV conditions using X-ray photoelectron spectroscopy (XPS), ultra violet photoelectron spectroscopy (UPS), and inverse photoemission spectroscopy (IPES).&nbsp; Water and ammonia adsorption on a polycrystalline thorium surface has been investigated at 100 and 298 K.&nbsp; Water adsorbs and dissociates upon the surface, leading to the formation of oxide and hydroxide species at 298 K, and oxide, hydroxide, and physisorbed water at 100 K. The surfaces after adsorption at both temperatures proved to be unstable when exposed to the low energy electron gun utilised in IPES.&nbsp; Ammonia adsorbs and dissociates upon the surface, leading to the formation of nitride and NH<sub>2</sub> species at 298 K, and nitride, NH<sub>2</sub>, and physisorbed ammonia at 100 K.&nbsp; Upon reaction only the mononitride ThN is formed, the metallic nature of which was confirmed by UPS and IPES.&nbsp; The surface was unstable under the low energy electron gun utilised in IPES, with the ThN species being converted to the non-metallic Th<sub>3</sub>N<sub>4</sub>.&nbsp; Water and ammonia adsorption on a polycrystalline uranium surface has also been investigated at 100 and 298 K.&nbsp; Water adsorbs and dissociates upon the surface, leading to the formation of oxide and hydroxide species at 298 K, and oxide, hydroxide, and physisorbed water at 100 K.&nbsp; The rate of reaction of water with uranium is substantially reduced in the presence of residual oxygen on the surface.&nbsp; The small band-gap of semi-conducting UO<sub>2</sub> can be observed directly with UPS and IPES.&nbsp; Ammonia adsorbs and dissociates upon the surface, leading to the formation of nitride and NH<sub>2</sub> species at 100 and 298 K.

Item Type: Thesis (PhD)
Status: Unpublished
Date of First Compliant Deposit: 30 March 2016
Last Modified: 08 Jan 2014 15:14
URI: http://orca-mwe.cf.ac.uk/id/eprint/54193

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