A. V. Knyazev

Isomorphism and phase diagram of the Pb5(PO4)3Cl-Pb5(VO4)3Cl system

Compounds of composition Pb5(PxV1−xO4)3Cl (0 ≤ x ≤ 1), which are synthetic analogues of minerals pyromorphite, vanadinite, and endlichite, were synthesized for the first time by high-temperature solid-phase reactions. X-ray diffraction and IR spectroscopy were used to determine the structure of the compounds and revealed complete miscibility in the solid phase of the Pb5(PO4)3Cl-Pb5(VO4)3Cl binary system. Adiabatic reaction calorimetry was used to determine standard enthalpies of mixing and formation and showed that the regular solutions model is applicable to the Pb5(PO4)3Cl-Pb5(VO4)3Cl system. Differential thermal analysis in tandem with high-temperature X-ray diffraction was used to study the phase diagram and characterize phase transitions.

The thermodynamic properties of calcium uranoborate

The standard enthalpy of formation of crystalline Ca(BUO5)2 at 298.15 K was determined by reaction calorimetry (−4491.0 ± 3.5 kJ/mol). The heat capacity of the substance was measured over the temperature range 7–304 K by adiabatic vacuum calorimetry, and its thermodynamic functions were calculated. The standard entropy and the Gibbs function of formation at 298.15 K were found to be −887.1 ± 2.1 J/(mol K) and-4226.5 ± 4.0 kJ/mol, respectively. The standard thermodynamic functions of calcium uranoborate synthesis reactions were calculated and analyzed.

Synthesis, structures, and physicochemical properties of Sr2AIIUO6 (AII = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Zn, and Cd) compounds

Sr2AIIUO6 (AII = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Zn, and Cd) compounds were synthesized by high-temperature reactions in the solid phase. The crystal structure (space group P21/n) was refined by the Rietveld method for Sr2MgUO6, (Sr0.5Ba0.5)2SrUO4, and Sr2CdUO6, which were synthesized for the first time. IR spectral characteristics were studied. The standard enthalpies of formation of the compounds were determined by reaction calorimetry.

Synthesis and study of uranosilicates of the uranophane-kasolite group

A series of uranosilicates of alkali (Li, Na, K, Rb, Cs, NH4), alkaline-earth (Mg, Ca, Sr, Ba), and rare-earth (Y, La, Ln) elements were prepared by precipitation from a solution under hydrothermal conditions. The composition and structure of the compounds were examined by X-ray diffraction analysis, IR spectroscopy, and thermal analysis. It was established that these compounds belong to the uranophane Mk[HSiUO6]k·nH2O and kasolite M2k[SiUO6]k·nH2O mineral groups.

The thermodynamic properties of Ba2SrUO6

The standard enthalpy of formation of crystalline Ba2SrUO6 at 298.15 K was determined by reaction calorimetry (-2940.0 ± 8.5 kJ/mol). The heat capacity of the compound was measured over the temperature range 8-330 K by adiabatic vacuum calorimetry. The thermodynamic functions of Ba2SrUO6 were calculated. The standard entropy (-558.6 ± 2.1 J/(mol K)) and Gibbs function of formation at 298.15 K (-2773.5 ± 9.0 kJ/mol) were determined.

Synthesis and characterization of MIIU3O10 · nH2O (MII = Mg, Mn, Co, Ni, Cu, Zn, Cd) triuranates

Individual crystalline phases of composition MIIU3O10 · nH2O were prepared by reacting schoepite UO3 · 2.25H2O with aqueous solutions of Mg, Mn, Co, Ni, Cu, Zn, or Cd nitrates under hydrothermal conditions at 200°C. The composition and structure of the resultant compounds were determined by hightemperature X-ray diffraction, IR spectroscopy, scanning calorimetry, and chemical analysis; the dehydration and thermal destruction of the compounds were studied.

Crystal structure of the perovskites Ba2AIIUO6 (AII = Zn, Cd, Pb)

AbstractThe compounds Ba2ZnUO6, Ba2CdUO6, and Ba2PbUO6 were prepared by high-temperature solidphase reactions. Their structures (space group Fm

Thermochemistry and thermal characteristics of Ba2MIIUO6 (MII = Mg, Ca, Sr, Ba)

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