Effect of cationic composition of electrolytes based on the M2MoO4-M2Mo2O7-UO2MoO4 (M = Li, Na, K, Cs) system on the oxygen factor of the uranium electrolytic oxides

The effects of the electrolyte composition, deposition potential, temperature, and the salt-solvent cation on the oxygen factor (the [O]/[U] atomic ratio) of uranium oxides obtained by potentiostatic electrolysis of molybdate melts are studied. It is shown that the oxygen factor of the cathodic product increases with the melt temperature. The shift of the deposition potential toward more electronegative values, an increase in the Mo₂O^2? ₇ ion concentration, and a decrease in the UO₂MoO₄ concentration favor the cathodic formation of uranium oxides with lower oxygen factors. All other conditions being the same, the oxygen factor decreases with increasing the salt-solvent cation radius. The observed anomalous behavior of the Li₂MoO₄-based electrolytes can be caused by a lower activity in the melts of the O^2? anions that are capable of forming stable complexes Li₃O⁺ with lithium cations. The obtained results can be reasonably explained in terms of the model of ionic composition of the uranyl-containing tungstate melts, which is based on the concept of involvement of the uranyl ions in the complexes’ formation and stepwise solvolysis.     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

Phase relations in the systems M2MoO4-Cr2(MoO4)3-Zr(MoO4)2 (M = Li, Na, or Rb)

Phase equilibria in the systems M₂MoO₄-Cr₂(MoO₄)₃-Zr(MoO₄)₂ (M = Li, Na, or Rb) were investigated by X-ray powder diffraction analysis, DTA, and IR spectroscopy. The subsolidus structure of the phase diagrams of the systems under study was established. Two phases are formed in the Rb₂MoO₄-Cr₂(MoO₄)₃-Zr(MoO₄)₂ system with the molar ratios of the starting components equal to 5: 1: 1 (S ₂) and 1: 1: 1 (S ₁). Proceeding from that the isostructurality of Rb₅FeHf(MoO₄)₆ and S ₂ the unit cell, parameters are determined for S ₂.     

Interrelation between the physicochemical properties of MnCl2-MCl (M = Li, Na, K, Rb, and Cs) melts

Our own experimental studies of vapor pressure and surface tension were used to analyze isotherms of various types of the properties under consideration. The data obtained were processed using a mathematical model to calculate the molar surface and excess molar Gibbs energy, which clearly indicated that the surface properties obeyed the general rules that governed changes in these properties of solutions according to the position of alkali metals in the periodic table of the elements. The data on various physicochemical properties of the cesium chloride-manganese chloride system are evidence of the presence of singular extremum points on concentration dependence isotherms.     

New Layered Polyborates Cs(2)M(2)B(10)O(17) (M = Na, K)

The polyborates Cs(2)M(2)B(10)O(17) (M = Na, K) have been prepared and their structures determined by single-crystal X-ray diffraction methods. They crystallize in the monoclinic space group C2/c (Z = 8) with unit-cell parameters a = 21.643(3) ?, b = 6.558(2) ?, c = 11.072(2) ?, beta = 105.43(1) degrees, V = 1514.8(6) ?(3) for the Na compound and a = 22.547(9) ?, b = 6.614(2) ?, c = 11.288(4) ?, beta = 103.25 degrees, V = 1638.3(8) ?(3) for the K analogue. The new structural type contains a 2-dimensional borate matrix that is built from a complete condensation of the ring system B(5)O(11). The Cs atoms reside within the borate matrix, and the Na (K) atoms are placed between the thick Cs borate sheets.     

Thermodynamics of dehydration of MAsUO6·xH2O (M = Li,Na, K,Rb, Cs) Crystal Hydrates

The existence regions of crystal hydrates in the systems MAsUO₆-H₂O (M = Li, Na, K, Rb, Cs) in the coordinates water vapor pressure-temperature were studied by the isopiestic method and static tensimetry. All individual compounds formed in these systems were isolated and studied by reaction calorimetry. The enthalpies of their formation and dehydration were determined.     

Effect of cationic composition of melts M2WO4-M2W2O7-UO2WO4 (M = Li, Na, K, Cs) and parameters of electrolysis to uranium dioxide electrodeposition characteristics

The effect of solvent salt cation, temperature of electrolysis, and cathodic deposition potential to basic characteristics of uranium dioxide potentiostatic electrodeposition (cathodic current efficiency, current density, and product deposition rate) in electrolyte system M₂WO₄-M₂W₂O₇-UO₂WO₄ (M = Li, Na, K, Cs) was studied in air. A conclusion was made that optimum electrodeposition and production of deposits not contaminated with supporting electrolyte decomposition products need higher cathodic polarization close to the solvent decomposition potentials and higher temperatures (up to 900°C). A melt based on K₂WO₄ was selected as the electrolyte providing satisfactory electrodeposition parameters of uranium dioxide with the composition close to stoichiometric.     

Phase formation in the Re-Se-Br-MBr systems (M = Li, Na, K, Rb, Cs)

Phase formation in the Re-Se-Br-MBr systems (M = K, Rb, Cs) was studied by NMR spectroscopy and powder X-ray diffraction. The reactions taking place in alkali metal halide melts were found to give, among the series of cluster anions [{Re₆Se_{8 − n} Br _n }Br₆]^{(4 − n)}− (0 ≤ n≤ 4), polymeric complexes Re₆Se₈Br ₂ and M₂Re₆Se₈Br₄ (M = Cs, Rb) and salts containing cluster anions [Re₆Se₆Br₈]²⁻ and [Re₆Se₇Br₇]³⁻ as the major products. The effect of the alkali metal cation on the product composition and ratio was established. Original Russian Text ? S.S. Yarovoi, Yu.V. Mironov, S.V. Tkachev, V.E. Fyodorov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 344–349.     

Synthesis and crystal structure of new complex oxides K10M2+Mo7O27 (M2+ = Mg, Mn, Co)

New compounds, K₁₀M²⁺ Mo₇O₂₇ (M²⁺ = Mg, Mn, Co), have been synthesized and characterized. The compounds have an original structure, as established for the first two phases (orthorhombic, space group Pnm2₁, Z = 2, a = 18353 and 18.402, b = 7.889 and 7.931, c = 10.566 and 10.604 å, R = 0.0345 and 0.0609, respectively). A specific feature of the structure is isolated clusters consisting of face-sharing MoO₆ and M²⁺O₆ octahedra, each of the latter having six MoO4 tetrahedra attached to it by vertices. The general pseudohexagonal motif of the structure of the phases is similar to that of glaserites.     

Les systemes binaires AlPO4−M3PO4 (M=Li,Na, K)

The liquid-solid phase diagram of the binary systems AlPO₄?M₃PO₄(M=Li, Na, K) have been established. The additional compounds Na₃Al(PO₄)₂, Na₃Al₂(PO₄)₃ and K₃Al₂(PO₄)₃ have been found again. A new compound K₃Al(PO₄)₂ is observed. The melting point of Na₃PO₄ is 1545°C and K₃PO₄ does not melt up to 1700°C.     

Photocatalytic activity and intercalation of layered perovskite-like tantalates ANdTa2O7 (A = H,Li, Na,K, Rb,Cs)

Layered perovskite-like oxides ANdTa₂O₇ (A = H, Li, Na, K, Rb, Cs) were synthesized and characterized by means of diffuse reflection spectroscopy, thermogravimetry, and simultaneous thermal and X-ray phase analysis. Comparative analysis of the photocatalytic activity of ANdTa₂O₇ in the UV-induced hydrogen evolution from an aqueous isopropanol solution was performed. NaNdTa₂O₇ and HNdTa₂O₇ are able to intercalate water to the interlayer space. The compositions and thermal stability ranges of intercalates were determined. No explicit correlation between the photocatalytic activity of layered oxides and their ability to intercalate water to the interlayer space was found.     

Immobilization of molten salt waste into MZr2(PO4)3 (M=Li, Na, Cs, Sr)

Summary Amorphous zirconium phosphate (Zr(HPO₄)₂^.nH₂O, AM-ZP) has been investigated as a material for selective removal of Cs or Sr from molten salt waste at aqueous state and its ceramic waste form. NZP (MZr₂P₃O₁₂, M=Li, Na, Cs, and Sr), was synthesized by three methods and evaluated their durability by the Product Consistency Test (PCT) method. AM-ZP has a high selectivity on Cs and Sr even in the presence of Li with high concentration. From the leaching data, the leached fractions (LF_∞) of each product at a given time in infinite leachate volume can be calculated by a semi-empirical equation. The LF_∞ of Li, Na, Cs and Sr on the product prepared by composition-adjusting process were 0.143, 0.078, 0.017, and 0.034, respectively. It can be concluded that AM-ZP is an effective material for selective removal of radionuclides from molten salt waste and its metal-loaded ZP can be changed into a durable waste form close to NZP structure by a composition-adjusting process.     

MZr2（AsO4）3（M=Na,K,Rb,Cs）的水热合成与结构表征

用水热晶化法合成了MZr_2(ASO_4)_3(M=Na,K,Rb,Cs)系列化合物。研究了反应物浓度、配比及不同砷源等水热晶化条件对产物物相的影响。用XRD、IR和Raman光谱对产物进行了表征。4种晶体的振动光谱由钠到铯呈现出规律性变化。     

Isomerism and Vibration Spectra of M2XO4 Molecules (M = Li,Na, K; X = S,Se, Te,Cr, Mo,W)

The equilibrium geometries, isomerization energies, force fields, vibration frequencies, and band intensities in the IR spectra of M₂XO₄ molecules (M = Li, Na, K; X = S, Se, Te, Cr, Mo, W) were calculated ab initio by the Hartree-Fock method in extended basis sets using relativistic effective core potentials. The relative energies of alternative structures were refined by the configuration interaction method taking into account single- and double-excited configurations, with the Davidson correction for quartic excitations. The results show that the chemical bonds between the metal atom and the acid residue XO₄ are highly polar. The majority of M₂XO₄ molecules have two isomers. In both isomers the XO₄ ^{2 -} anion coordinates the metal cations M⁺ in the bisbidentate (bb) fashion. The equilibrium configurations ofthe nuclei in the ground (bb) and excited (bb') isomers have the D ₂ d and C _s symmetry, respectively. In the bb isomer, the cations coordinate at the opposite, and in the bb' isomer, at the adjacent edges of the XO₄ ^{2 -} anion, having the shape of a distorted tetrahedron. The relative energy of the bb' isomer is 9-28 kJ mol^{- 1}. The energy barriers to intramolecular rearrangements bb'(C _4s) bb(D _{2 d}) are also low: 15-35 kJ mol^{- 1}. These results show that the M₂XO₄ molecules are structurally nonrigid, with a polytopic character of the M-XO₄ chemical bonds. The calculation results were compared to the published experimental data on the structure and vibration spectra of the M₂XO₄ molecules.