Dissolution of UO<Subscript>2</Subscript> in the N<Subscript>2</Subscript>O<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The kinetics of the UO₂ dissolution in the N₂O₄-H₂O system was studied. At 25°C, the process is kinetically controlled, whereas at 55°C the process occurs initially under kinetic control (3 min) and then under diffusion-kinetic control. At 80°C, the process occurs exclusively under diffusion-kinetic control. The apparent activation energy was estimated at ∼39 kJ mol⁻¹.     

Valence state of atoms in the perovskite-like phase Sr<Subscript>x</Subscript>Cu<Subscript>3</Subscript>V <Subscript>4</Subscript>O<Subscript>12</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.67−1.0) and its properties

We report the first synthesis, at high pressure and temperature (p = 6.0?8.0 GPa, t = 1000°C), of Sr_xCu₃V₄O₁₂ (x = 0.67?1.0), a cation-deficient perovskite-like phase of variable composition (sp. gr. Im \(\bar 3\), Z = 2). Using x-ray photoelectron spectroscopy, we have determined the binding energies and valence states of atoms in Sr_xCu₃V₄O₁₂. The stoichiometric composition of this phase can be represented by the chemical formula Sr²⁺Cu²⁺Cu ₂ ⁺ (V ₂ ⁵⁺ V ₂ ⁴⁺ )O₁₂. Air exposure leads to the formation of SrCO₃ and Sr(OH)₂ on its surface and to the oxidation of univalent copper and tetravalent vanadium. According to IR spectroscopy data, the penta-and tetravalent vanadium in the high-pressure phase is in octahedral oxygen coordination. The electrical conductivity, magnetic susceptibility, thermal properties, and ion selectivity of this compound have been investigated.     

Laser interference method of determining the parameters of gas bubbles

The fundamentals of the laser interference method of determining the parameters of gas bubbles in liquids and solids are considered. The role of polarization in the development of interference bands is analyzed. Features in the realization of an experimental plant and a technique for performing experiments are presented.     

Ga NMR and magnetic susceptibility in δ-phase of Pu1−xGax (x = 0.05, x = 0.08) alloys

⁶⁹Ga nuclear magnetic resonance spectra, line shifts (⁶⁹K) and nuclear spin-lattice relaxation rate have been measured in the 20 years aged Pu_0.95Ga_0.05 and in fresh prepared Pu_0.92Ga_0.08 alloys, stabilized δ-phase, at magnetic field of 9.4 T in the temperature range (10-500) K. The line shift and are determined correspondingly by the static and fluctuating-in-time parts of the local magnetic field that originates in transferred hyperfine coupling the Ga nuclear spin with the nearest f-electron environment of more magnetic Pu.Temperature behavior of the resonance properties is found the same in fresh Pu_0.92Ga_0.08 and aged Pu_0.95Ga_0.05 alloy. The NMR results are in favor that δ-phase of Pu_1−xGa_x alloys represents at T > 200 K the Kondo lattice, in which the localized electronic spins fluctuate independently from each other without any macroscopic coherence. The coherent state like in heavy-fermion liquids emerges in Pu_0.95Ga_0.05 below T^∗ = 200 K. A little bit higher estimate of crossover temperature T^∗ = 250 K was founded for Pu_0.92Ga_0.08.     

Production of Biochar and Other High Value-Added Products from Biomass by Wet Torrefaction in Fluidized Bed in Superheated Steam Environment

Chemical and Petroleum Engineering - The advantages of wet torrefaction of biomass by superheated steam in fluidized bed over conventional hydrothermal carbonization method are confirmed. The...     

Mechanochemical preparation,sintering aids and hybrid microwave sintering in the proton conductor Sr0.02La0.98Nb1-xVxO4-δ, x = 0, 0.15

Mechanochemical preparation of Sr_0.02La_0.98Nb_1-xV_xO_4-δ was demonstrated for values of x = 0 and 0.15. Crystallinity could be improved by calcining at 1073 K. On cooling, the high temperature scheelite phase was retained to room temperature. Several novel sintering additives for LaNbO₄ materials have been tested. The most successful were Cu₃Nb₂O₈ and CuV₂O₆, which reduced the temperature of maximum shrinkage rate to temperatures ∼1173 K. The additive CuV₂O₆ was shown to increase densification and promote grain growth. A mechanosynthesised sample of Sr_0.02La_0.98Nb_0.85V_0.15O_4-δ + 2 mol% CuV₂O₆ could be densified to ∼ 90% that of the theoretical by hybrid microwave sintering at 1168 K for 5 min. The scheelite phase in this material was retained to room temperature, against the normal thermodynamic tendency. Impedance spectroscopy in wet and dry, nitrogen and oxygen atmospheres suggested that the bulk conductivity of this material is unaffected by the sintering aid, whereas the grain boundary conductivity was impaired and exhibited n-type conductivity behaviour, characteristic of the additive. The concentration of this promising additive should be reduced in further work.