Foley Bryan J, Christian Jonathan H, Klug Christopher A, Villa-Aleman Eliel, Wellons Matthew S, DeVore Michael, Groden Nicholas, Darvin Jason
Savannah River National Laboratory, Aiken, SC 29803, USA.
Naval Research Laboratory, Washington, D.C. 20375, USA.
Dalton Trans. 2022 Apr 12;51(15):6061-6067. doi: 10.1039/d2dt00196a.
This manuscript describes the chemical transformations that occur during hydrolysis of uranium tetrafluoride (UF) due to its storage in humid air (85% and 50% relative humidity) at ambient temperatures. This hydrolysis was previously reported to proceed slowly or not at all (depending on the percent relative humidity); however, previous reports relied primarily on X-ray diffraction methods to probe uranium speciation. In our report, we employ a battery of physiochemical probing techniques to explore potential hydrolysis, including Raman spectroscopy, powder X-ray diffraction, F nuclear magnetic resonance spectroscopy, scanning electron microscopy, and focused ion beam microscopy with energy-dispersive X-ray spectroscopy. Of these, only Raman spectroscopy proved to be particularly useful at observing chemical changes to UF. It was found that anhydrous UF slightly oxidizes over the course of thirteen days to Schoepite-like uranium complexes and possibly UO. In contrast, UF exposed to 50% relative humidity slightly decomposes into UOF, Schoepite-like uranium complexes, and possibly a high order uranium oxide that eluded chemical assignment (UO). Despite the rich chemical speciation observed in our Raman spectroscopy measurements, X-ray diffraction and F NMR measurements on the same material showed no changes. Microscopy measurements suggest that the observed reactions between UF and water occur primarily on the surface of UF particulates a method that is visually similar to surface corrosion of metals. Therefore, we postulate that NMR spectroscopy and X-ray diffraction, which are well-suited for bulk analysis, are less suited than Raman spectroscopy to observe the surface-based reactions that occur to UF when exposed to humid air. Considering the importance of UF in the production of nuclear fuel and weapons, the results presented herein are widely applicable to numerous nuclear science fields where uranium detection and speciation in humid environments is of value, including nuclear nonproliferation and nuclear forensics.
本手稿描述了四氟化铀（UF）在室温下于潮湿空气中（相对湿度分别为85%和50%）储存时发生的化学转化过程。此前报道称这种水解反应进行缓慢或根本不发生（取决于相对湿度百分比）；然而，先前的报告主要依靠X射线衍射方法来探测铀的形态。在我们的报告中，我们采用了一系列物理化学探测技术来探究潜在的水解反应，包括拉曼光谱、粉末X射线衍射、氟核磁共振光谱、扫描电子显微镜以及配备能量色散X射线光谱的聚焦离子束显微镜。其中，只有拉曼光谱在观察四氟化铀的化学变化方面被证明特别有用。研究发现，无水四氟化铀在十三天的时间里会轻微氧化成水磷铀矿类铀配合物，可能还有UO。相比之下，暴露在50%相对湿度下的四氟化铀会轻微分解成UOF、水磷铀矿类铀配合物，可能还有一种难以进行化学鉴定的高阶铀氧化物（UO）。尽管在我们的拉曼光谱测量中观察到了丰富的化学形态，但对同一材料进行的X射线衍射和氟核磁共振测量却未显示出变化。显微镜测量表明，观察到的四氟化铀与水之间的反应主要发生在四氟化铀颗粒的表面——这一方式在视觉上类似于金属的表面腐蚀。因此，我们推测，适合进行体相分析的核磁共振光谱和X射线衍射，在观察四氟化铀暴露于潮湿空气中时发生的基于表面的反应方面，不如拉曼光谱适用。考虑到四氟化铀在核燃料和武器生产中的重要性，本文所呈现的结果广泛适用于众多核科学领域，在这些领域中，潮湿环境下铀的检测和形态分析具有重要价值，包括核不扩散和核取证。
