I. D. Zakir’YAnova

Molten systems based on alkali metal halides with lithium oxide additives are promising as a working medium on pyrochemical reprocessing of nuclear waste. A mixture of alkali metal fluorides of eutectic composition (FLiNaK) is a suggested solvent due to the high solubility of actinide oxides, low viscosity, high boiling points, low vapor pressure and resistance to radiation damage. Thermal analysis, XRD, Raman spectroscopy and thermodynamic simulations were used to obtain evidences on the phase equilibria and liquidus points of the system (0.85 FLiNaK?0.15 CeF3)?Li2O, containing up to 8.8 mol. % lithium oxide. The solubility of lithium oxide in the fluoride melt FLiNaK? ?CeF3 and the thermodynamic parameters of dissolution were obtained. The eutectic point (the Li2O content is 3.1 mol. %, Tm = 489 ??) and two peritectic points (lithium oxide content are 3.2 and 4.2 mol. %, and liquidus points are 497 and 549 ??, respectively) were found. Thermodynamic simulation results show an exothermic effect due to interaction between lithium oxide and fluoride melt. The interaction product oxyfluoride CeOF was detected by XRD analysis and Raman spectroscopy.

Rare earth metal chlorides are used as starting materials on electrochemical synthesis of pure metals. These chlorides are hygroscopic and tend to form hydrates. To resolve the uncertainty of the thermal behavior of the hydrates LaCl3 ∙ 7H2O, NdCl3 ∙ 6H2O, SmCl3 ∙ 6H2O, and YbCl3 ∙ 6H2O, a comprehensive study is carried out. Thermogravimetry, differential scanning calorimetry and mass spectrometry were used to reveal the dehydration and hydrolysis processes over the temperature range of 25–700 ºC. Phase compositions of the initial hydrates, intermediate and final products are investigated by the XRD analysis, Raman and IR spectroscopy. Distinctions in the thermal behavior of the studied hydrates were found. The features must be taken into account when obtaining anhydrous rare earth chlorides and in technological processes with its participation.

The mechanism and kinetic parameters of the interaction of the FLiNaK–CeF₃ melt with water vapors and oxygen in the air atmosphere were determined using Raman and IR spectroscopy, XRD analysis, and thermodynamic modeling of processes. The presence of the 4CeF_3(solution) + 6H₂O _(gas) + O_2(gas) = 4CeO_2(solid) + 12HF_(gas) reaction, which disturbs the fluoride melt homogeneity, was verified in situ by Raman spectroscopy adopted for high-temperature, chemically aggressive fluoride systems. Based on the obtained spectral data, the type of the kinetic equation, order, and rate constant of the chemical reaction were determined. The concentration of cerium dioxide was found to increase linearly in time and a zero reaction order with respect to CeO₂ was detected. The change in the concentration of CeO₂ over time at T = 510 °C is described by the equation C = 0.085t; the reaction rate constant is 0.085 mol. %∙min⁻¹. The obtained kinetic parameters may be used to model emergencies related with the depressurization of the coolant circuit or the working area of the molten salt reactor.

The electrical conductivity of LiCl?GdCl3 molten systems with the gadolinium chloride additions ranging from 0 to 23 mol % was measured depending on both the temperature and concentration of GdCl3. The molar conductivity of the molten GdCl3?LiCl system is calculated taking into account the assumption of additivity of the molar volume of the mixture. The obtained temperature dependencies can be approximated by Arrhenius-type equation. The effective activation energy, Ea, increased with the GdCl3 content. The liquidus temperatures of the studied systems were determined by differential scanning calorimetry. The high-temperature Raman spectra of LiCl?GdCl3 chloride melts were recorded. In addition, the conductivity of 0.77LiCl?0.23GdCl3 molten system with 1 mol % of Gd2O3 was measured. The investigation demonstrates that the addition of gadolinium oxide results in a decrease of the conductivity of the chloride molten system and growth of its liquidus temperature

The structure, conductivity, melting points and caloric melting effects of the (Li2CO3-Na2CO3-K2CO3)eut melt/MgO nanopowder heterogeneous system with MgO concentration up to 70 vol % have been investigated. A wide variety of methods (DSC, XRD, BET, high resolution scanning electron microscope, AC impedance method, IR and Raman spectroscopy) were used to evaluate samples and research. It is revealed that at the values of effective thickness of the salt phase interlayer between MgO particles below 100 nm there is an abrupt decrease in the melting points of the salt and the normalized phase transition enthalpy of the heterogeneous system. The activation energy of the electrical conductivity rises as the values of effective thickness of the melt phase interlayer between MgO particles decreases. The study established the lack of any chemical interaction between MgO and carbonate melt at 400-600°С. In situ Raman spectroscopy of the (Li2CO3-Na2CO3-K2CO3)eut melt/MgO nanopowder systems revealed the solvation of solid particles by salt-melt ions.

The thermodynamic parameters of the heterogeneous Li2CO3–Na2CO3–K2CO3–MgO nanopowder system are detemined by differential scanning calorimetry (DSC). The melting temperature and the reduced...

—The thermal dehydration of GdCl3 ⋅ 6H2O crystalline hydrate is studied by synchronous thermal analysis and mass spectrometry using certified samples. The mechanism and the caloric effects of...

The conductivities of the disperse system α-Al2O3–molten carbonate chloride mixture Li2CO3–Na2CO3–K2CO3–NaCl are dtermined in the temperature range 455–550°C. As follows from Raman spectroscopy data,...

The structure and the conductivity of homogeneous CsCl–PbCl₂–PbO melts with different compositions are studied. The Raman spectra (RS) of the chloride and oxide–chloride melts containing lead oxide have been measured. It is found that the CsCl (71.3 mol %)–PbCl₂ (28.7 mol %) system with the addition of 12 mol % PbO and the CsCl (18.3 mol %)–PbCl₂ (81.7 mol %) system with the addition of 18 mol % PbO contain Pb₃O₂Cl⁺ oxide–chloride groups. The temperature dependences of the electrical conductivity are measured in the PbCl₂–CsCl chloride melts containing 28.7 and 81.7 mol % lead chloride and in homogeneous molten mixtures CsCl (71.3 mol %)–PbCl₂ (28.7 mol %) with the addition of 12 mol % PbO and the CsCl (18.3 mol %)–PbCl₂ (81.7 mol %) with the addition of 18 mol % PbO. Significant degradation of the ion conductive properties of the PbO–PbCl₂–CsCl oxide–chloride melts as compared to those of the PbCl₂–CsCl chloride electrolytes has been revealed. It is shown that the decrease in the electrical conductivity of the PbCl₂–CsCl oxide–chloride melts as lead oxide is added is due to the presence of Pb₃O₂Cl⁺ oxide–chloride groups.