Solid-Liquid Equilibria in the Quaternary Systems KCl–MgCl<Subscript>2</Subscript>–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O and NaCl–KCl–SrCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 348 K

Solid-liquid equilibria in the quaternary systems KCl–MgCl₂–SrCl₂–H₂O and NaCl–KCl–SrCl₂–H₂O at 348 K were measured by the isothermal solution saturation method. The composition of the equilibrium solid phase, solubilities of salts, and densities of saturated solution in the two systems were determined. Phase diagrams, water content diagrams and solution density diagrams of quaternary systems were plotted according to experimental data. The phase diagram of the quaternary system NaCl–KCl–SrCl₂–H₂O has one invariant point, three univariant curves as the boundary of NaCl, KCl and SrCl₂ · 2H₂O. This phase diagrams were simple co-saturation type without complex salt and solid solution. For the quaternary system KCl–MgCl₂–SrCl₂–H₂O, one complex salt KCl · MgCl₂ · 6H₂O (Car) had been found in this system, consisted of five univariant curves, two invariant points and four crystallization regions of MgCl₂ · 6H₂O (Bis), KCl, SrCl₂ · 2H₂O and KCl · MgCl₂ · 6H₂O. And the densities transformation rules were simply discussed. Simultaneously, the solubilities and densities data in invariant point of the quaternary system NaCl–KCl–SrCl₂–H₂O had been compared with the experimental data of previous researchers.     

Phase diagram of the NaCl–MgCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system at 25–75°C and its application for MgCl<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O purification

The co-saturation line for the solid phases NaCl_(s) and MgCl₂ · 6H₂O_(s) in aqueous solution has been measured by a phase equilibrium at various temperatures. It was found that the Y _b (Y _b = w(NaCl)/(w(NaCl) + w(MgCl₂))) value of the co-saturation line increase with increasing temperature. A new recrystallization approach has been suggested for the purification of MgCl₂ · 6H₂O_(s) containing quite amount of impurity NaCl, i.e., dissolving the crude sample at low temperatures, followed by evaporating and phase separating at high temperatures. Applying the proposed approach a crude MgCl₂ · 6H₂O_(s) sample can be purified to the level of Y _b = 0.17% by only one crystallization process.     

Phase equilibria in the ZnGeAs<Subscript>2</Subscript>–MnAs system

The ZnGeAs₂–MnAs system is a eutectic-type system as determined by X-ray powder diffraction, DTA, and microstructure observation, with the eutectic coordinates: 61 mol % ZnGeAs₂ mol %, 39 mol % MnAs, and T_m = 816°C. The eutectic is a lamellar eutectic as shown by microstructure examination. A characteristic feature of the system is a small mutual solubility of the components. Precision analysis of diffraction patterns enabled us to refine unit cell parameters for cubic and tetragonal ZnGeAs₂ phases. MnAs in alloys is shown to consist of a hexagonal phase and a orthorhombic phase. ZnGeAs₂ and MnAs alloys are ferromagnets (T_C ~ 320 K). Their magnetization increases in response to increasing MnAs content.     

Phase and extraction equilibria in H<Subscript>2</Subscript>O–sulfonol–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) and H<Subscript>2</Subscript>O–sodium dodecyl sulfate–HCl (H<Subscript>2</Subscript>SO<Subscript>4</Subscript>) systems

Solubility isotherms of water–sulfonol–hydrochloric (or sulfuric) acid and water–sodium dodecyl sulfate–hydrochloric acid systems at 75°C and a water–sodium dodecyl sulfate–sulfuric acid system at 50°C are constructed. Regions of two-phase liquid equilibrium suitable for use in extraction are found. Concentration parameters for extraction are determined. The interfacial distribution of a series of metal ions with and without such additional complexing reagents as diantipyrylmethane and diantipyrylheptane is studied.     

Formation of binary salts in the system LiCl–CsCl–H<Subscript>2</Subscript>O

In the ternary system LiCl–CsCl–H₂O the binary salt LiCl·2CsCl·4H₂O was formed. Its structure was proved by the X-ray structural analysis. The binary compound formed in the aqueous solution by the structurally-forced insertion mechanism.     

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.     

The NaCl–AlCl<Subscript>3</Subscript>–HCl–H<Subscript>2</Subscript>O system at 25°С

Solubility was studied in the system NaCl–AlCl₃–HCl–H₂O at 25°C in the section 28 wt % HCl. The system is of the eutonic type and has an extensive sodium chloride crystallization region. The composition of the eutonic solution is the following, wt %: NaCl, 0.47; AlCl₃ ? 6H₂O, 8.88; HCl, 25.38; and H₂O, 65.27. The lines of saturated solutions were approximated by polynomial equations.     

Phase Diagram of Quaternary System NaBr–KBr–CaBr<Subscript>2</Subscript>–H<Subscript>2</Subscript>O at 323 K

The phase equilibria in the system NaBr–KBr–CaBr₂–H₂O at 323 K were studied using the isothermal dissolution equilibrium method. Using the experimental solubilities of salts data, phase diagram was constructed. The phase diagram have two invariant points, five univariant curves, and four crystallization fields. The equilibrium solid phases in the system are NaBr, NaBr · 2H₂O, KBr, and CaBr₂ · 4H₂O. The solubilities of salts in the system at 323 K were calculated by Pitzer’s equation. There is shown that the calculated solubilities agree well with experimental data.     

Solubility in the ternary system LiCl + MgCl<Subscript>2</Subscript> + H<Subscript>2</Subscript>O at 60 and 75°C

The solubility of ternary system of lithium, magnesium and chloride and refractive indexes have been determined at 60 and 75°C, respectively. Using the experimental results, the phase diagrams of the ternary system were plotted. The single-salt Pitzer parameters of LiCl and MgCl₂ β⁽⁰⁾, β⁽¹⁾ and C ^ϕ were calculated by using the equations reported by Li Y-H and de Lima at different temperatures, respectively. On the basis of Pitzer ion-interaction model and solubility product equation for mixed electrolytes, the mixing parameters θ_{Li, Mg}, Ψ_{Li, Mg, Cl} and equilibrium constant K _sp were evaluated in this system, which were not reported in literature. A complete phase diagram of the ternary system was predicted at 60 and 75°C. The prediction of solubilities in ternary system was then demonstrated. The calculated solubilities agreed well with the experimental values.     

Phase equilibria in a ternary fullerenol-d(C<Subscript>60</Subscript>(OH)<Subscript>22–24</Subscript>)–SmCl<Subscript>3</Subscript>–H<Subscript>2</Subscript>O system at 25°C

The solubility in a ternary fullerenol-d (C₆₀(OH)_22–24)–SmCl₃–H₂O system at 25°C is studied via isothermal saturation in ampules. The solubility diagram is shown to be a simple eutonic one that consists of two branches corresponding to the crystallization of fullerenol-d (C₆₀(OH)_22–24 · 30H₂O) and samarium(III) chloride SmCl₃ · 6H₂O crystallohydrates and contains one nonvariant eutonic point corresponding to saturation with both crystallohydrates. The long branch of C₆₀(OH)_22–24 · 30H₂O crystallization shows the effect of fullerenol-d salting out of saturated solutions; in contrast, the short branch of SmCl₃ · 6H₂O crystallization shows the pronounced salting-in effect of samarium(III) chloride.     

Phase equilibria in the MgS–In<Subscript>2</Subscript>S<Subscript>3</Subscript> system

Phase equilibria in the MgS–In₂S₃ system were studied. This system is of the dystectic type with a limited region of a solid solution based on β-In₂S₃. In the MgS–In₂S₃ system, a compound of the composition MgIn₂S₄ forms, which forms congruently at 1180 K and crystallizes in the cubic system (space group Fd3m) with the unit cell parameter a = 1.0689 nm. Eutectics have the compositions 47 and 62 mol % In₂S₃ and the melting points 1150 and 1120 K, respectively. The MgS solubility in β-In₂S₃ at 1070 K reaches 9 mol % MgS.     

Phase equilibria in the BaS–Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> system

In the BaS–Ga₂S₃ system, the following compounds form: congruently melting compound BaGa₄S₇ (rhombic system, space group Pmn2₁, a = 1.477 nm, b = 0.624 nm, c = 0.593 nm, and T_melt = 1490 K) and incongruently melting compounds BaGa₂S₄ (cubic system, space group Pa3, a = 1.2661 nm, and Tmelt = 1370 K), Ba₂Ga₂S₅ (monoclinic system, space group C2/c, a = 1.529, b = 1.479, c = 0.858 nm, ß = 106.04°, and T_melt = 1150 K), Ba₃Ga₂S₆ (monoclinic system, space group C2/c, a = 0.909 nm, b = 1.448 nm, c = 0.903 nm, ß = 91.81°, and T_melt = 1190 K), Ba₄Ga₂S₇ (monoclinic system, space group P2₁/m, a = 1.177 nm, b = 0.716 nm, c = 0.903 nm, ß = 108.32°, and T_melt = 1230 K), and Ba₅Ga₂S₈ (rhombic system, space group Cmca, a = 2.249 nm, b = 1.215 nm, c = 1.189 nm, and T_melt = 1480 K). The compositions of eutectics are 38 and 72 mol % Ga₂S₃, and their melting points are 1120 and 1160 K, respectively. The BaS solubility in γ-Ga₂S₃ at 1070 K reaches 3 mol %.     

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.     

Phase equilibria in the Cu–Cu<Subscript>2</Subscript>Se–As system

Phase equilibria in the Cu–Cu₂Se–As were investigated by differential thermal analysis and X-ray powder diffraction analysis. Informative plots describing this system were constructed, viz., the polythermal sections Cu_0.667Se_0.333–As, Cu_0.667Se_0.333–Cu_0.735As_0.265, and Cu_0.8Se_0.2–As, the isothermal section of the phase diagram at 300 K, and the projection of the liquidus surface. The obtained results differ from the published data in length of fields of primary crystallization of phases and in coordinates of a number of invariant equilibrium points.     

Measurement of mineral solubilities in the ternary systems NaCl−ZnCl<Subscript>2</Subscript>−H<Subscript>2</Subscript>O and MgCl<Subscript>2</Subscript>−ZnCl<Subscript>2</Subscript>−H<Subscript>2</Subscript>O at 373 K

In this work, the solubilities of the salt minerals and the densities of solution in two ternary systems sodium chloride–zinc chloride–water and magnesium chloride–zinc chloride–water were measured at 373 K using an isothermal solution saturation method. Based on the determined equilibrium solubility data and the corresponding equilibrium solid phase, the phase diagrams and density diagrams of the two systems were plotted. The results show that the two ternary systems are complex and the eutectic points, the univariant solubility curves and the solid crystalline phase regions are shown and discussed. The phase diagram of the ternary system NaCl?ZnCl₂?H₂O at 373 K is constituted of two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to NaCl, ZnCl₂ and 2NaCl · ZnCl₂. And the phase diagram of the ternary system MgCl₂?ZnCl₂?H₂O at 373 K includes two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to MgCl₂ · 6H₂O, MgCl₂ · ZnCl₂ · 5H₂O and ZnCl₂. The experimental results were simply discussed.     

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.     

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.     

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.     

Phase equilibria in the Na,K‖CO<Subscript>3</Subscript>,HCO<Subscript>3</Subscript>,F-H<Subscript>2</Subscript>O system at 25°C

Phase equilibria in the Na,K‖CO₃,HCO₃,F-H₂O system at 25°C are studied by the translation method. Twenty nine double-saturation divariant fields, 31 triple-saturation monovariant curves, and 11 quadruple-saturation points for equilibrium solid phases are distinguished in the system. The first looped phase diagram (phase complex) of the title system is designed.     

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.