Characterizing the solid hydrolysis product, UF4(H2O)2.5, generated from neat water reactions with UF4 at room temperature

Chemical and spectroscopic characterization of plutonium tetrafluoride

Anhydrous plutonium tetrafluoride is an important intermediate in the production of metallic Pu. This historically important compound is also known to exist in at least two distinct, yet understudied hydrate forms, PuF4·xH2O(s) (0.5 ≤ x ≤ 2) and PuF4·2.5H2O(s). X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) are the most common tools used to characterize these materials, often in a context for studying structural and morphological changes that arise from aging or calcination. However, fundamental electronic and vibrational spectroscopic information is rather scarce. Here, we measured the visible and shortwave infrared (SWIR) diffuse reflectance, Fourier transform infrared (FTIR), fluorescence and Raman spectra of PuF4(s) and PuF4·xH2O(s) to obtain a better electronic and vibrational fingerprint. Our work provides clear indication of the polymeric structure of anhydrous PuF4, consistent with the Raman spectrum of UF4(s) and its hydrates. This is supplemented with XRD, TGA and SEM analysis. Findings in this study indicate that the spectra are modified by particle size, which in turn is influenced by synthetic technique.

Synthesis and Morphological Control of UO2F2 Particulates

Uranium-based microspheres are of interest due to their potential applications as targets for medical isotopes production, as fuel for nuclear reactors, and as standardized materials for nuclear forensics. Here, for the first time, UO₂F₂ microspheres (1-2 μm) have been prepared from the reaction between UO₃ microspheres and AgHF₂ in an autoclave. In this preparation, a new fluorination method has been applied, and HF_(g)-produced in situ from the thermal decomposition of AgHF₂ and NH₄HF₂-was used as the fluorinating agent. The microspheres were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Diffraction results indicated that the reaction performed with AgHF₂ at 200 °C led to anhydrous UO₂F₂ microspheres, while at 150 °C, hydrated UO₂F₂ microspheres were obtained. Meanwhile, NH₄HF₂ led to the formation of contaminated products as driven by the formation of volatile species.

Probing the hydrolytic degradation of UF4 in humid air

This manuscript describes the chemical transformations that occur during hydrolysis of uranium tetrafluoride (UF₄) 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, ¹⁹F 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 UF₄. It was found that anhydrous UF₄ slightly oxidizes over the course of thirteen days to Schoepite-like uranium complexes and possibly UO₃. In contrast, UF₄ exposed to 50% relative humidity slightly decomposes into UO₂F₂, Schoepite-like uranium complexes, and possibly a high order uranium oxide that eluded chemical assignment (U_xO_y). Despite the rich chemical speciation observed in our Raman spectroscopy measurements, X-ray diffraction and ¹⁹F NMR measurements on the same material showed no changes. Microscopy measurements suggest that the observed reactions between UF₄ and water occur primarily on the surface of UF₄ particulates via 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 UF₄ when exposed to humid air. Considering the importance of UF₄ 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.