Energetics of hydration on uranium oxide and peroxide surfaces
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, Sergey V. Ushakov3, Tatiana Shvareva3, Hongwu Xu4,
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Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, USA; and Department of Chemistry, Washington State University, Pullman, Washington 99164, USA 2 Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, USA; Department of Chemistry, Washington State University, Pullman, Washington 99164, USA; and The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99164, USA 3 Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, California 95616, USA 4 Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] c) e-mail: [email protected] d) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/editor-manuscripts/. Received: 2 April 2019; accepted: 13 May 2019
Enthalpies of water adsorption on amorphous and crystalline oxides and peroxides of uranium are reported. Despite substantial structural and computational research on reactions between actinides and water, understanding their surface interactions from the energetic perspective remains incomplete. Direct calorimetric measurements of hydration energetics of nano-sized, bulk-sized UO2, U3O8, anhydrous c-UO3, amorphous UO3, and U2O7 were carried out, and their integral adsorption enthalpies were determined to be −67.0, −70.2, −73.0, −84.1, −61.6, and −83.6 kJ/mol water, with corresponding water coverages of 4.6, 4.5, 4.1, 5.2, 4.4, and 4.1 H2O per nm2, respectively. These energetic constraints are important for understanding the interfacial phenomena between water and U-containing phases. Additionally, this set of data also helps predict the absorption and desorption behavior of water from nuclear waste forms or used nuclear fuels under repository conditions. There are also underlying relations for water coverage among different U compounds. These experimentally determined data can be used as benchmark values for future computational investigations.
Introduction The interaction of uranium phases with water is an important topic as it is closely linked to nuclear fuel storage, repository research, and environmental concerns of nuclear waste contamination. Water can interact with actinides in multiple ways, including sorption, radiolysis, and hydrothermal chemical reactions, which result in numerous interesting and important phenomena. Specifically, water may participate as a catalyst in the oxidation of U(IV) [and Pu(IV)] binary oxides where molecular oxygen alone hardly oxidizes the dioxides [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Water also enhances the corrosion rate of actinides and associated fis
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