Phase diagrams of the KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript> and KF-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> systems

The phase diagrams of the systems KF-K₂TaF₇ and KF-Ta₂O₅ were determined using the thermal analysis method. The phase diagrams were described by suitable thermodynamic model. In the system KF-K₂TaF₇ eutectic points at x _KF=0.716 and t=725.4°C and at x _KF=0.214 and t=712.2°C has been calculated. It was suggested that K₂TaF₇ melts incongruently at around 743°C forming two immiscible liquids. The system KF-Ta₂O₅ have been measured up to 8 mol% of Ta₂O₅. The eutectic point was estimated to be at x _KF∼0.9 and t∼816°C. The formation of KTaO₃ and K₃TaO₂F₄ compounds has been observed in the solidified samples.     

Structural and thermal studies on the solid products in the system MnSeO<Subscript>3</Subscript>-SeO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

The solubility of MnSeO₃-SeO₂-H₂O system was studied in the temperature region 25–300°C. The compounds of the three-component system were identified by the Schreinemaker’s method. The phase diagram of manganese(II) selenites was drawn and the crystallization fields for the different phases were determined. Depending on the conditions for hydrothermal synthesis, MnSeO₃·H₂O, MnSeO₃·3/4H₂O, MnSeO₃·l/3H₂O and MnSe₂O₅ were obtained. The different phases were proven and characterized by chemical, powder X-ray diffraction and thermal analyses, as well as IR spectroscopy. The kinetics of dehydration and decomposition of MnSeO₃·H₂O was studied under non-isothermal heating. Based on 4 calculation procedures and 27 kinetic equations, the values of activation energy and pre-exponential factor in Arrhenius equation were calculated for both processes.     

Study of the crystallization fields of cobalt(II) slenites in the system CoSeO<Subscript>3</Subscript>-SeO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

Summary The solubility of CoSeO₃-SeO₂-H₂O system in the temperature region 298-573 K was studied. The phase diagram of cobalt(II)selenites was drawn and the crystallization fields for the different phases were determined. Depending on the conditions for hydrothermal synthesis, CoSeO₃×2H₂O, α-CoSeO₃×1/3H₂O, β-CoSeO₃×1/3H₂O, CoSeO₃, Co(HSeO₃)₂×2H₂O and CoSe₂O₅ were obtained. The different phases were proved and characterized by chemical and X-ray analyses, as well as IR spectroscopy.     

Phases in the system Tb<Subscript>2</Subscript>O<Subscript>3</Subscript>-SeO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O at 100°C and their physicochemical study

Summary The solubility isotherm of the system Tb₂O₃-SeO₂-H₂O at 100° was studied. The compounds of the three-component system were identified by the Schreinemakers’ method as well as by chemical and X-ray phase analyses. Simultaneous TG and DTA analyses of all compounds of the system were made. The mechanism of thermal decomposition was described.     

Phase equilibria in the Ce<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Ce₂O₃-K₂O-P₂O₅ ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K₄Ce₂P₄O₁₅ has been found. Phase diagram and isothermal section at room temperature of the system Ce₂O₃-K₂O-P₂O₅ have been presented.     

Phase transition of YBO<Subscript>3</Subscript>

Yttrium orthoborate crystallizes in the vaterite-type structure and has two polymorphous forms, viz. a low- und a high temperature one. DTA measurements of YBO₃ confirmed a reversible phase transition with a large thermal hysteresis. The phase transition has been accurately characterized by the application of different heating and cooling rates (β). Consequently, the extrapolation of the experimental data to zero β yields the transition points at 986.9°C for the heating up and at 596.5°C for the cooling down cycle. These values correspond to samples just after treatment at 1350°C. For samples with a different ‘thermal history’ other phase transition temperatures are observed, (e.g. after having performed several heating and cooling cycles). The linear relationship between the associated DTA signal ΔT=T _onset–T _offset and the square root of the heating rate β was confirmed, but the relation between T _onset and square root of β is not found here. From the empirical data a good linear fitting between T _onset and ln(β+1) can be derived. From the kinetic analysis (Kissinger method) of the phase transformation of YBO₃ an apparent activation energy of about 1386 kJ mol^–1 for heating and of about 568 kJ mol^–1 for cooling can be determined     

Liquid-solid metastable phase equilibria for the quaternary system (NaCl-KCl-CaCl<Subscript>2</Subscript>-H<Subscript>2</Subscript>O) at 308.15 K

The solubility and the physicochemical properties (densities, viscosities, refractive indices, conductivities and pH) in the liquid-solid metastable system (NaCl-KCl-CaCl₂-H₂O) at 308.15 K have been investigated using the isothermal evaporation method, and the dry-salt phase diagram, water-phase diagram, and the diagram of physicochemical properties vs. composition in the system were plotted. One three-salt cosaturated point, three metastable solubility isotherm curves, and three crystallization regions corresponding to sodium chloride, potassium chloride and calcium chloride tetrahydrate were formed, and neither solid solution nor double salts were found. On the basis of the extended Harvie-Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β⁽⁰⁾, β⁽¹⁾, C ^ϕ for NaCl, KCl and CaCl₂, the mixing ion-interaction parameters θ_Na,K, θ_Na,Ca, θ_K,Ca, Ψ_Na,K,Cl, Ψ_Na,Ca,Cl, Ψ_K,Ca,Cl, and the Debye-Hückel parameter A ^ϕ and the chemical potentials of the minerals in the quaternary system at 308.15 K were fitted, and the predictive solubility based on the temperature-dependent equation and the chemical potentials of the minerals agrees well with the experimental data.     

Computational investigation into the phase transitions from AlPO<Subscript>4</Subscript>-H<Subscript>3</Subscript>

Open-framework aluminophosphates constitute an important family of materials due to their enormous potential applications in catalysis, exchange and gas separation, such as aluminosilicate zeolites. These compounds, whose formations are promoted by the presence of organic templates, are constructed from alternation of AlO4 and PO4 tetrahedral with an Al/P ratio of unity. However, there are quite a number of AlPOs that contain 5- or 6-coordinated Al atoms which are coordinated to extra-fram…     

Kinetics and thermodynamics of thermal decomposition of synthetic AlPO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O

Cumene hydroperoxide (CHP) and its derivatives have caused many serious explosions and fires in Taiwan as a consequence of thermal instability, chemical contamination, and even mechanical shock. It has been employed in polymerization for producing phenol and dicumyl peroxide (DCPO). Differential scanning calorimetry (DSC) was used to analyze the thermal hazard of CHP in the presence of sodium hydroxide (NaOH), sulfuric acid (H₂SO₄), and sodium bisulfite (Na₂SO₃). Thermokinetic parameters for decomposition, such as exothermic onset temperature (T ₀ ), maximum temperature (T _max ), and enthalpy (ΔH), were obtained from the thermal curves. Isothermal microcalorimetry (thermal activity monitor, TAM) was employed to investigate the thermal hazards during CHP storage and CHP mixed with NaOH, H₂SO₄, and Na₂SO₃ under isothermal conditions in a reactor or container. Tests by TAM indicated that from 70 to 90 °C an autocatalytic reaction was apparent in the thermal curves. According to the results from the TAM test, high performance liquid chromatography (HPLC) was, in turn, adopted to analyze the result of concentration versus time. By the Arrhenius equation, the activation energy (E _a ) and rate constant (k) were calculated. Depending on the process conditions, NaOH was one of the incompatible chemicals or catalysts for CHP. When CHP is mixed with NaOH, the T ₀ is induced earlier and the reactions become more complex than for pure CHP, and the E _a is lower than for pure CHP.     

Phase diagram of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript>-Ag<Subscript>2</Subscript>O system

The results concerning the synthesis, structure and thermal properties of V₂O₅-MoO₃-Ag₂O samples in the vanadium rich region of ternary system are presented in the form of quasi-binary phase diagrams in which at constant V₂O₅/MoO₃ molar ratios, equal 9:1, 7:3 and 1:1, the content of Ag₂O was variable. A new ternary phase isostructural with NaVMoO₆ has been detected in the investigated system.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Glasses in the CuNbOF<Subscript>5</Subscript>-BaF<Subscript>2</Subscript> and CuNbOF<Subscript>5</Subscript>-PbF<Subscript>2</Subscript> systems

Nonhygroscopic, colored glasses have been synthesized in the CuNbOF₅-BaF₂ and CuNbOF₅-PbF₂ systems proceeding from crystals of the complex compound CuNbOF₅ · 4H₂O. The glasses have been studied structurally and thermally. The crystallization resistance of the glasses has been studied as a function of glass composition. Lead difluoride glasses are more stable than barium difluoride glasses of the same composition. These glasses have lower glass-transition temperatures than the binary glasses formed in the NbO₂F-BaF₂ system. The glass structure is built of Nb(O,F)₆ polyhedra, which are linked in glass networks through oxygen bridges. Modifier cations influence both the structure of glass networks and the linkage of polyhedra.     

Interactions in the system Mn(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-HCONH<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

Solubilities and solid phases in the system Mn(NO₃)₂-HCONH₂-H₂O were studied by an isothermal method at 25°C. The congruently saturating compound Mn(NO₃)₂ · 2HCONH₂ · 2H₂O was isolated; the concentration conditions for its crystallization in the system were determined. The solid phases of the system were characterized by physicochemical methods (X-ray powder diffraction, differential thermal analysis, IR spectroscopy, and crystal-optical analysis).     

Phase equilibria in the CdI<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The phase diagram of the system CdI₂-Bi₂O₃ is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. As a result of the synthetic and peritectic interactions, two incongruently melting intermediate phases i.e. phase A — CdI₂·2Bi₂O₃ and phase B — CdI₂·4Bi₂O₃ (stable in the temperature interval 370–850°C) are formed.The phase A exists in two polymorphic forms with a temperature of the phase transition T =320–370°C. The unit cell parameters at low temperature modification of -CdI₂°2Bi₂O₃ were determined. (a=1.032 nm, b=1.046 nm, c=1.046 nm, =115.02°, =109.11° and =82.04°). The phases A and B have fields of homogeneity.The authors acknowledge thankfully the financial support for this work from the Ministry of Education and Science (Fond Scientific investigations — contract TN-1102).     

Physicochemical properties of KOH-H<Subscript>2</Subscript>O<Subscript>2</Subscript>-H<Subscript>2</Subscript>O solutions

Density, viscosity, and surface tension of KOH-H₂O₂-H₂O solutions used to synthesize potassium superoxide in sprayer apparatus were studied with various relative amounts of the components in the temperature range 0–30°C. Analytical dependences of the above-mentioned quantities on temperature and solvent (water) content of the system were found.     

Bleaching of kraft cellulose by the ClO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript> scheme

The influence of conditions of a two-stage treatment of deciduous and coniferous kraft cellulose (by the ClO₂-H₂O₂ scheme) on the degree of its delignification and bleaching was studied. The optimum ratio of reagents in each stage of the treatment was elucidated.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1735–1738.Original Russian Text Copyright © 2004 by Shcherbakova, Demin.     

Solid vitreous inorganic electrolytes in Li<Subscript>2</Subscript>O-LiF-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system for rechargeable lithium power sources: Ionic conductivity and activation energy

The effect of chemical composition to ionic conductivity and activation energy of vitreous solid electrolytes (SE) based on Li₂O-P₂O₅-LiF system (Li₂O ≥ 45.4 mol %) was detected. The temperature effect to conductivity and activation energy was studied. An original technology was designed to prepare vitreous SEs in Li₂O-P₂O₅-LiF system containing up to 20 mol % LiF and characterized with ionic conductivity up to 4.4 × 10^?7 S cm^?1 (24°C) and activation energy about 0.567 eV. The synthesized materials are characterized with high X-ray amorphism and technological performance.     

Physicochemical simulation of calcite (dolomite)-FeSO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O open systems

Effect of the chemical composition of carbonate minerals on the precipitation of iron from a Fe(II) sulfate solution was studied.     

Anionic complexes as products of reactions in SO<Subscript>2</Subscript>-carbamide(acetamide)-H<Subscript>2</Subscript>O systems

Evaluation of the contribution of hydrosulfite and pyrosulfite ions in the formation of anionic complexes in the sulfur(IV) oxide-amide-water systems was carried out considering the data of the pH-metric and redox-metric studies. Microconstants of the formation of anionic complexes of carbamide and acetamide with the above-mentioned anions were calculated.     

Kinetics of the oxidation of diethyl sulfide in the B(OH)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O system

Data obtained for the kinetics of oxidation of diethyl sulfide (Et₂S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O₂H)(OH) ₃ ⁻ and diperoxoborates B(O₂H)₂(OH) ₂ ⁻ are the active species. The rates of the reactions of Et₂S with B(O₂H)(OH) ₃ ⁻ and B(O₂H)₂(OH) ₂ ⁻ are 2.5 and 100 times greater than with H₂O₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 38–42, January–February, 2007.