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Using a new, low-temperature, fluoride-based process, thorium nitride imide of the chemical formula Th2N2(NH) was synthesized from thorium dioxide via an ammonium thorium fluoride intermediate. The resulting product phase was characterized by powder X-ray diffraction (XRD) analysis and was found to be crystallographically similar to Th2N3. Its unit cell was hexagonal with a space group of P3m̅1 and lattice parameters of a = b = 3.886(1) and c = 6.185(2) Å. The presence of -NH in the nitride phase was verified by Fourier transform infrared spectroscopy (FTIR). Total energy calculations performed using all-electron scalar relativistic density functional theory (DFT) showed that the hydrogen atom in the Th2N2(NH) prefers to bond with nitrogen atoms occupying 1a Wyckoff positions of the unit cell. Lattice fringe disruptions observed in nanoparticle areas of the nitride species by high-resolution transmission electron microscopic (HRTEM) images also displayed some evidence for the presence of -NH group. As ThO2 was identified as an impurity, possible reaction mechanisms involving its formation are discussed. [ABSTRACT FROM AUTHOR]

A low-temperature fluoride route was utilized to synthesize neptunium mononitride, NpN. Through the development of this process, two new neptunium nitride species, NpN2 and Np2N3, were identified. The NpN2 and Np2N3 have crystal structures isomorphous to those of UN2 and U2N3, respectively. NpN2 crystallizes in a face-centered cubic CaF2-type structure with a space group of Fm3m and a refined lattice parameter of 5.3236(1) Å. The Np2N3 adopts the body-centered cubic Mn2O3-type structure with a space group of Ia3. Its refined lattice parameter is 10.6513(4) Å. The NpN synthesis at temperatures ≤900 °C using the fluoride route discussed here was also demonstrated. Previous computational studies of the neptunium nitride system have focused exclusively on the NpN phase because no evidence was reported experimentally on the presence of NpNx systems. Here, the crystal structures of NpN2 and Np2N3 are discussed for the first time, confirming the experimental results by density functional calculations (DFT). These DFT calculations were performed within the local-density approximation (LDA+U) and the generalized-gradient approximation (GGA+U) corrected with an effective Hubbard parameter to account for the strong on-site Coulomb repulsion between Np 5f electrons. The effects of the spin-orbit coupling in the GGA+U calculations have also been investigated for NpN2 and NpN. [ABSTRACT FROM AUTHOR]

The synthesis of (U,Th)O2 solid solutions at a relatively low temperature of 1100 °C using a new technique is described. First, separate actinide oxides were reacted with ammonium hydrogen fluoride to form ammonium actinide fluorides at room temperature. Subsequently, this fluoride was converted to an actinide oxide solid solution using a two-phase reaction process, which involved heating of the fluoride first at 610 °C in static air followed by heating at 1100 °C in flowing argon. Oxide solid solutions of UO2 and ThO2 were synthesized for a ThO2 content from 10 to 90 wt %. Microscopic investigation showed that the (U,Th)O2 solid solutions synthesized using this method had high crystallinity and homogeneity up to nanoscale. [ABSTRACT FROM AUTHOR]

The reaction mechanism and kinetics of the thermal decomposition of uranium dinitride/uranium sesquinitride to uranium mononitide under inert atmosphere at elevated temperature were studied. An increase in the lattice parameter of the UN2/α-U2N3 phase was observed as the reaction temperature increased, corresponding to a continuous removal of nitrogen. Electron density calculations for these two compounds using XRD powder patterns of the samples utilizing charge-flipping technique were performed for the first time to visualize the decrease in nitrogen level as a function of temperature. Complete decomposition of UN2 into tα-U2N3 at 675 °C and the UN formation after a partial decomposition of α-U2N3 at 975 °C were also identified in this study. The activation energy for the decomposition of the UN2/α-U2N3 phase into UN, 423.8 ± 0.3 kJ/mol (101.3 kcal/mol), was determined under an inert argon atmosphere and is reported here experimentally for the first time. [ABSTRACT FROM AUTHOR]

A new method for the preparation of Tc metal from pertechnetate is described. Metallic technetium was prepared from TcO by initial reduction in dry argon atmosphere at 300 °C followed by a wet argon atmosphere in the presence of carbon between 700 and 910 °C. The higher temperature conditions in the presence of H2O and carbon form H2 and CO, which can drive the reduction of TcO2. This method was applied to the recovery of pertechnetate sorbed on anion-exchange resins resulting in the formation of Tc metal microspheres. The resulting Tc was characterized by XRD analysis and SEM. [ABSTRACT FROM AUTHOR]

The incorporation of various cations such as Zn2+ into the structure of fluorapatite, Ca5(PO4)3F, is governed by the effectiveness of the cations to substitute for Ca2+ ions. In this work different concentrations of zinc were used to substitute for calcium. Microscopic characterization was done by observing the nanostructural variations induced by these zinc substitutions and by relating these observations to thermal behavior of the zinc-substituted fluorapatite. Random incorporation of zinc into the fluorapatite structure and the zinc induced amorphization effects oriented in the nanostructure of fluorapatite led to phase impurities of zinc-substituted fluorapatites when the amount of zinc used was greater than 25 mol % of the total cation concentration. It also was observed that the thermal stability of the samples decreased with increasing zinc concentration. Among the zinc-incorporated samples, the most similar chemical and physical properties to the single-phased fluorapatite were identified in the sample containing the lowest amount of zinc (25 mol %). After calcination, however, this sample showed to contain some defects in the atomic arrangement of the nanostructure which led to a thermal instability of the fluorapatite. [ABSTRACT FROM AUTHOR]

The oxidative ammonolysis route was used to synthesize three uranium nitrides, UN2, U2N3, and UN, using UF4 as the starting material. Powder XRD analysis showed the UN2 and U2N3 products to contain less than 1.0 wt % uranium oxides. UO2 level was identified to be 5.0 (0) wt % in the UN product as it is made, but this level increases upon exposure to air. The morphology of these nitrides was studied with SEM, while the microstructures of UN2 and U2N3 were investigated by TEM techniques for the first time. An explicit microstructural characterization of UN is also presented. These characterizations showed that UN has a long-range order in its structure and bulk of the UO2 impurities present on the UN microparticle surface, likely originating from minute oxygen impurities in the inert atmosphere cover gas and/or diffusion through the quartz reactor tube at high temperatures. Surface area measurements demonstrated a 10-fold increase in surface area during the ammonolysis step, from 0.03 to 0.26 m2/g, and minimal change during the denitriding step. HRTEM reveals a long-range order in the microstructure of the UN. There are three different multiplicities of tunnel rows. These tunnels correspond to 2-, 3-, and 4-fold multiplicities, which are further confirmed by the corresponding intensity profiles in a, b, and c, respectively. [ABSTRACT FROM AUTHOR]