Phase equilibria in the NaCl–NaBO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–KCl quaternary system

The phase diagrams of the ternary systems NaCl–NaBO₂–KCl, NaCl–KCl–Na₂CO₃, and KCl–NaBO₂–Na₂CO₃ and the quaternary system NaCl–NaBO₂–Na₂CO₃–KCl were studied by the calculation–experimental method and differential thermal analysis. Analytical models of phase equilibria were obtained, and the coordinates of ternary eutectics and a quaternary eutectic. It was shown that low-melting eutectic melts can be used as media for synthesizing oxide tungsten bronzes.     

Diagram of the PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript> system

A phase diagram of the PbF₂–SnF₂ system has been studied by differential thermal analysis and X-ray powder diffraction. The system forms Pb_1–хSn_хF₂ (х ≤ 0.33) solid solution and three compounds. Pb₂SnF₆ decomposes in solid state by a peritectoid reaction at 350°С; Pb₃Sn₂F₁₀ and PbSnF₄ melt by peritectic reactions at 565 and 380°С, respectively. The eutectic coordinates are 180°С, 90 mol % SnF₂.     

Dissociation enthalpies and phase equilibrium for TBAB semi-clathrate hydrates of N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>, N<Subscript>2</Subscript> + CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> + CO<Subscript>2</Subscript>

Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N₂ and CO₂ and gases mixtures such as N₂ +  CO₂ and CH₄ +  CO₂ were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N₂ for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26.     

Study of the NaF–NaBr–Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> system

The NaBr–D (Na₃FSO₄) quasi-binary system and the NaF–NaBr–Na₂SO₄ ternary system were studied by differential thermal analysis. The melting points and compositions of eutectic mixtures were determined, and in-, mono-, and divariant equilibrium states were described.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Possibility of using an UV–nano-TiO<Subscript>2</Subscript>–K<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript> system for the determination of COD

The results of a study of the optimum oxidation conditions in the system UV?nano-Т?О₂–K₂Cr₂O₇ in a specially designed photoreactor are presented. The basic parameters of the photocatalytic oxidation of glucose and acetic acid were studied and optimized. The oxidation of organic compounds under the optimized conditions was studied. Nano-TiO₂ was shown to be a promising photocatalyst in the design of new oxidation systems for analytical purposes.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Modifying additives affect the properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effects caused by modifying additives, namely nonionic surfactants (Tween 80 and Neonol AF 9-6) and oxides (B₂O₃ and HfO₂), on the rheology, film formation, and phase formation in the yttrium aluminum silicate system prepared by sol–gel technology were studied. The effect of 1 wt % HfO₂ additions on the activation energy of crystallization was studied.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Structure and thermal properties of the fritted glazes in SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaO–MgO–Na<Subscript>2</Subscript>O–K<Subscript>2</Subscript>O–ZnO system

In this work, the structure and thermal properties of aluminosilicate fritted glazes in SiO₂–Al₂O₃–CaO–MgO–Na₂O–K₂O–ZnO system with (4.0 mol%) and without addition of ZnO were examined by GIXRD, FTIR, MAS-NMR and thermal methods (DTA, DIL). It has been found that the all experimental glazes are amorphous material (transparent glazes). On the base of spectroscopic investigations, it was found that zinc ions exist in the network glazes in the octahedral coordination—Zn²⁺ ions play a network modifier role in structure of glazes. An analysis of the data obtained from thermal tests showed that addition of ZnO into chemical composition results in decrease in glass transition temperature value (T _g) for all glazes (DTA, DIL). The coefficient of thermal expansion (α) is decreased as the whole measurement range for one series of fritted glazes.     

Regularities of formation of complex oxides with the fluorite structure in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystal and local structures of the complex oxides (1–x)ZrO₂ ? xY₂O₃ (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.     

Oxidative leaching of uranium from SIMFUEL using Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O<Subscript>2</Subscript> solution

A feasibility and basic study to find a possibility to develop such a process for recovering U alone from spent fuel by using the methods of an oxidative leaching and a precipitation of U in high alkaline carbonate media was newly suggested with the characteristics of a highly enhanced proliferation-resistance and more environmental friendliness. This study has focused on the examination of an oxidative leaching of uranium from SIMFUEL powders contained 16 elements (U, Ce, Gd, La, Nd, Pr, Sm, Eu, Y, Mo, Pd, Ru, Zr, Ba, Sr, and Te) using a Na₂CO₃ solution with hydrogen peroxide. U₃O₈ was dissolved more rapidly than UO₂ in a carbonate solution. However, in the presence of H₂O₂, we can find out that the leaching rates of the reduced SIMFUEL powder are faster than the oxidized SIMFUEL powder. In carbonate solutions with hydrogen peroxide, uranium oxides were dissolved in the form of uranyl peroxo-carbonato complexes. UO₂(O₂) _x (CO₃) _y ^2−2x−2y , where x/y has 1/2, 2/1.     

Magnetic phase diagrams of the Tm<Subscript>2</Subscript>Fe<Subscript>17</Subscript>–H system

The compound Tm₂Fe₁₇, the only one among R₂Fe₁₇ (where R is a rare earth metal), exhibits uniaxial magnetic anisotropy at cryogenic temperatures. Its Curie temperature is close to room temperature, T_C = 295 K. Magnetic phase diagrams for the Tm₂Fe₁₇–H system have been constructed on the basis of measuring the temperature and field dependences of magnetization performed for different crystallographic directions of single-crystalline samples of Tm₂Fe₁₇ and its hydrides Tm₂Fe₁₇H_x (x = 1, 2, 3, 4). It has been found that the hydrogen atoms, located in the interstices of the crystal lattice of this compound, have a significant effect on both its Curie temperature and the type of magnetic anisotropy.     

Distribution of niobium and lanthanum between two immiscible melts in the system LaPO<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–NaF–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The system LaPO₄–SiO₂–NaF–Nb₂O₅–Fe₂O₃ is characterized by immiscibility fields in the liquid state region. Addition of iron expands fields of immiscibility of melts and decreases the temperature of their coexistence. A fraction of 87–90% of niobium is extracted into iron silicate melt, and 92–98% of lanthanum is extracted into phosphate salt melt.     

Phase equilibria in the PbBi<Subscript>2</Subscript>S<Subscript>4</Subscript>–PbSnS<Subscript>2</Subscript> system

The PbBi₂S₄–PbSnS₂ system was studied by physicochemical analysis methods, and its state diagram was constructed. The system is partially quasi-binary; regions of solid solutions based on PbSnS₂ are determined. At a ratio between the initial components of 1: 1, congruently melting compound Pb₂SnBi₂S₆ forms. The unit cells parameters of Pb₂SnBi₂S₆ crystallizing in the orthorhombic system are: a = 15.60 Å, b = 7.80 Å, c = 4.26 Å; space group Pbmm.     

Structural characterisation and thermo-physical properties of glasses in the Li<Subscript>2</Subscript>O–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O system

This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the system Li₂O–SiO₂–Al₂O₃–K₂O. A glass with nominal composition 23Li₂O–77SiO₂ (mol%) (labelled as L₂₃S₇₇) and glasses containing Al₂O₃ and K₂O with SiO₂/Li₂O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics (GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) depict the role of Al₂O₃ as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture of Q ³ and Q ⁴ (Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural features of glasses, phase composition and thermo-physical properties of GCs has been discussed.     

Phase equilibria in the CdAs<Subscript>2</Subscript>–Cd<Subscript>3</Subscript>As<Subscript>2</Subscript>–MnAs ternary system

We determined, using a set of physicochemical methods, including X-ray powder diffraction (XRD), differential thermal analysis, and microstructure studies, that the CdAs₂–Cd₃As₂–MnAs ternary system is bounded by three eutectic-type quasi-binary sections: Cd₃As₂–MnAs, CdAs₂–MnAs, and Cd₃As₂–CdAs₂. For Cd₃As₂–MnAs and CdAs₂–MnAs sections, the eutectic coordinates are, respectively, 75 mol % Cd₃As₂ + 25 mol % MnAs, T _m.eut = 604°C; and 92 mol % CdAs₂ + 8 mol % MnAs, T _m.eut = 608°C. These are rod eutectics. Manganese solubilities in Cd₃As₂ and CdAs₂ phases are insignificant and, according to XRD and SEM, they do not exceed 1 at %. The binary eutectics of the quasi-binary sections form ternary eutectic Cd₃As₂ + CdAs₂ + MnAs, whose average composition as probed by SEM is 34.5 at % Cd, 63 at % Cd and 2.5 at % As and T _m.eut = 600°C. Cadmium and manganese arsenide alloys are ferromagnets with the Curie point at ~320 K. The magnetic and electric properties are due to ferromagnetic MnAs microinclusions.     

Solubility in the diagonal sections of the 2KCl + Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> ⇆ 2KNO<Subscript>3</Subscript> + CaCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Solubility data in the diagonal sections of the quaternary reciprocal 2KCl + Ca(NO₃)₂ → 2KNO₃ + CaCl₂–H₂O system at 25 and 15°C are presented. It has been shown that the quaternary system has no stable diagonal at the studied temperatures, but contains a stable pair of salts, namely, potassium nitrate and calcium chloride. The obtained data can be used to optimize the thermal and concentrational parameters of the synthesis of potassium nitrate from calcium nitrate and potassium chloride.     

Phase equilibria in the Cu<Subscript>2</Subscript>S–La<Subscript>2</Subscript>S<Subscript>3</Subscript>–EuS system

Phase equilibria in the isothermal (970 K) and polythermal LaCuS₂–EuS, Cu₂S–EuLaCuS₃, LaCuS₂–EuLa₂S₄, and EuLaCuS₃–EuLa₂S₄ sections of the Cu₂S–La₂S₃–EuS system have been studied. EuLaCuS₃ (annealing at 1170 K) is of orthorhombic system, space group Pnma, a = 8.1366(1) Å, b = 4.0586(1) Å, c = 15.9822(2) Å, is isostructural to Ba₂MnS₃, and incongruently melts by the reaction EuLaCuS_3cryst (0.50 EuS; 0.50 LaCuS₂) ? 0.22 EuS SS (0.89 EuS; 0.11 LaCuS₂) + 0.78 liq (0.39 EuS; 0.61 LaCuS₂); ΔН = 52 J/g. The Cu₂S–La₂S3–EuS system has been found to contain five major subordinate triangles. At 970 K, tie-lines lie between EuLaCuS₃ and the Cu₂S, EuS, LaCuS₂, and EuLa₂S₄ phases and between the LaCuS₂ phase and the γ-La₂S₃–EuLa2S4 solid solution. Eutectics are formed between LaCuS₂ and EuLaCuS₃ at 26.0 mol % of EuS and T = 1373 K and between EuLaCuS3 and EuLa₂S₄ at 29.0 mol % of EuLa₂S₄ and T = 1533 K.