Ion Beam Analyses of Moisture Reaction for Single Crystal Lithium Deuteride
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.143
Ion Beam Analyses of Moisture Reaction for Single Crystal Lithium Deuteride C. Haertling1, R. J. Hanrahan Jr.2, Y. Wang1, C. Wetteland3 1
Los Alamos National Laboratory, Los Alamos, NM 87544
2
U.S. Department of Energy, Washington, D.C. 20585
3
University of Tennessee, Knoxville, TN 37996
ABSTRACT
Ion beam analyses were completed on single crystal LiD (lithium hydride with deuterium on the hydrogen sites) to determine products of hydrolysis with decarbonated H2O (with protiumhydrogen) in an inert gas. Rutherford backscattering spectrometry showed movement of oxygen into the bulk of LiD samples. Hydrolysis rates for the single crystal LiD showed relatively slow initial growth of an oxygen-containing layer. Final growth rates varied widely with H2O level, from 1010 to 1015 (atoms/cm2)/min. at 5.6 and 28 mmol/min. H2O respectively. Simulations of spectra show the hydrolysis product to be LiOH. Elastic recoil detection identifies the hydrogen in the hydroxide layer upon dosing with H2O (with natural, protiated hydrogen) as primarily protium. Micrographs showed island growth occurring initially, with convergence to a full-coverage hydrolysis layer.
INTRODUCTION: Lithium deuteride–LiD (a form of lithium hydride with deuterium on the hydrogen sites) is a highly reactive solid that can generate a number of products once exposed to environmental contaminants. These products form very readily and are ubiquitous where LiD is present. It is desired to better understand the reactions and products that occur during hydrolysis of LiD, as well as the kinetics of reactions. To more clearly discern the reactions occurring at hydrolysis layer interfaces, single crystal LiD was studied.
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Ion beam analysis offers advantages for the study of LiD reaction products. Elemental composition is measured, as well as the element position relative to depth into the sample. Thus, the reaction front is apparent due to the mass contrast, which for our studies, is between protium (reactant) and deuterium in the substrate. Additionally, the depth penetration capability of ion beam analysis is particularly suited for LiD, allowing the data to be modeled for determination of compounds. EXPERIMENTAL DETAILS Sample Preparation The LiD sample type was single crystal cleaved from large crystallites grown from the melt. The single crystal material contained 2H (deuterium) for hydrogen, and primarily 6Li for lithium. The single crystal pieces varied greatly in size, but generally ranged from ~0.6-1 mm square u 1-2 mm thickness. Ion channeling showed that the cleaved planes for the FCC structure were {100}. Figure 1 shows a photograph of a cleaved sample, and a scanning electron micrograph of a surface, which shows a lack of features. As LiD is highly
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