Metrics & MoreArticle RecommendationsABSTRACT: "Real-life" metals inevitably form the oxide layer, thus leading to complex initial hydriding processes, which are still unclear because of the experimental challenges in monitoring elemental steps including surface sorption, permeation, and concentration of hydrogen. In this study, the deuteride precipitation caused by the concentration of deuterium was successfully measured by the in situ small-angle neutron scattering (SANS) method, which used a selfdesigned reaction chamber to give rise to the scattering signals of the surface structure. In addition, in the measurements of activated cerium samples, surface sorption of deuterium could be modified to form a constant flow in order to further explore the initial hydriding processes. The formation of deuterides was found to occur as soon as deuterium was absorbed in the samples with a thin oxide layer and the subsequent growth of deuterides depended on the amount of consumed D 2 . However, the sample with a thick oxide layer showed the delayed precipitation of deuterides and the decelerated subsequent growth of deuterides without inhibiting the surface absorption of deuterium. The in situ SANS method showed the high sensitivity to the deuteride phase on the surface at a deuterium amount of 0.2 μmol cm −2 D 2 for cerium and a great potential in exploring the mechanism of early incipient stages of hydrogen reactions.
Uranium is widely used in the nuclear industry and it is well known that uranium hydride, UH 3 , forms when uranium is exposed to air. The associated volume change during this transition can cause the surface region to crack, compromising structural integrity. Here, hydriding regions beneath hydride surface craters are studied by secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Our results indicate that strain transition regions exist, which are induced by hydrogen with a certain thickness between hydride craters and the uranium bulk. The SIMS and XPS results suggest that hydrogen exists covalently with uranium and oxygen in these transition regions. A micro-scale induction period model based on the transition region and previous hydriding models is developed. Within the so-called micro-scale induction period, hydrogen diffuses and accumulates at particular sites before reaching the critical concentration required to form stoichiometric UH 3 in the transition regions.
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