The (NH 4) 2 ReX 6 (X = F, Cl, Br, I) salts have been investigated by x-ray absorption fine structure spectroscopy. The ReF distance determined by EXAFS in (NH 4) 2 ReF 6 (i.e., 1.95 Å) is in good agreement with the one determined by single crystal x-ray diffraction in A 2 ReF 6 salts (A = K, Rb, Cs). The XANES studies of (NH 4) 2 ReX 6 (X = F, Cl, Br, I) indicates that the positions of the absorption edge and of the white line are shifted to higher energy when moving from I to F. These shifts have been explained in terms of the crystal field splitting parameter and covalent charge carried by the Re atoms. Calculations of the XANES spectra of the ReX 6 2− (X = F, Cl, Br, I) anions at the Re-L 3 edge have been performed and the calculated shifts and intensity of the white lines reproduce well the experimental observations.
The thermal analysis behavior of C 6 H 6 N 3 [ReO 4 ] was studied by simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) up to 700 °C under argon. Such analysis afforded rhenium metal, which was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. XRD peak broadening due to crystallite size and lattice strain was analyzed by both Williamson−Hall (W−H) and Debye−Scherrer (D−S) methods. Efforts to isolate Re metal from the thermal treatment of benzotriazole (BTA = C 6 H 5 N 3 ) with NH 4 ReO 4 and Re 2 O 7 under various atmospheres and temperatures are also reported. The results provide a significant insight into the chemistry of group VII transition metals, investigate the potential use of benzotriazole as a reducing agent for metal productions, and demonstrate a successful convenient method for rhenium metal production, which could be applied to other refractory metals.
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 NH4HF2was 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.
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