Direct crystallization of silicate–phosphate glasses of NaCaPO4–SiO2 system

The subject of the study was silicate–phosphate glasses of NaCaPO₄–SiO₂ system which are precursors of glass–crystalline materials. Glass–crystalline materials of NaCaPO₄–SiO₂ system obtained via crystallization of glasses belong to a group of the so-called bioactive materials. In order to obtain glass–crystalline materials with pre-established parameters, it is necessary to conduct crystallization of glasses at specific conditions. In order to design direct crystallization process properly, it is necessary to know the structure and microstructure of the glassy precursor. Microscopic investigation showed that liquation takes place in all the studied glasses. Based on DSC examinations, it has been found out that crystallization of the glasses of NaCaPO₄–SiO₂ system is a multistep process. The presence of several clearly separated exothermic peaks in DSC curves of investigated glasses makes it possible to crystallize only the separated phase with the matrix remaining amorphous or vice versa. Conducted detailed X-ray and spectroscopic studies of the materials obtained by heating in a gradient furnace (in the temperature specified on the basis of DSC) showed that separated phase and matrix crystallizes separately. Therefore, bioactive glass–crystalline materials can be obtained due to the existence of the phase separation phenomenon and pre-established sizes of the crystalline phase.     

Preparation of thiazolidin-4-one derivatives using ZnO–NiO–NiFe2O4 nano-composite system

The hydrothermal synthesis of ZnO–NiO–NiFe₂O₄ nano-composite is reported. The sample was utilized to characterize via XRD, FE-SEM, EDS, FT-IR, UV–Vis, and BET techniques. The sample consisted of three different phases as ZnO (hexagonal), NiO (cubic), and NiFe₂O₄ (cubic) with the average particle size as 34 nm and specific surface area, average pore diameter, and pore volume as 64.35 m² g^?1, 13.02 nm, and 0.201 cm³ g^?1, respectively. Catalytic behavior of the nano-composite was investigated on the synthesis of thiazolidin-4-one derivatives under thermal and ultrasonic irradiation condition. Our results show that the catalytic activity of ZnO–NiO–NiFe₂O₄ nano-composite is much higher than ZnO, NiO, and NiFe₂O₄ metal oxides. All products were prepared in high yields with short reaction times. In addition, the catalyst was recovered for at least five times.

     

Thermodynamic properties of the system MgSO4–MnSO4–H2O at 298.15 K

The mixed aqueous electrolyte system magnesium and manganese sulfate has been studied with the hygrometric method at the temperature 298.15 K. The relative humidity of this system is measured at total molalities from 0.2 mol kg⁻¹ to about saturation of one of the solutes for different ionic-strength fractions y of MgSO₄ with y=0.2, 0.5 and 0.8. The obtained data allow the deduction of new thermodynamic parameters. The experimental results are compared with the predictions of ZSR rule. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y of MgSO₄.     

Photocatalytic degradation kinetics of methyl orange in TiO2–SiO2–NiFe2O4 aqueous suspensions

Photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄ suspensions was investigated. Adsorption studies revealed photocatalytic degradation occurred mainly on the surface of the TiO₂–SiO₂–NiFe₂O₄. The disappearance of the compound followed the zero-order kinetics according to the Langmuir–Hinshelwood model and the rate constant was 0.0035 mg L^?1 min^?1. The rate constant depended on the amount of photocatalyst, initial pH, and the presence of additional scavengers. ^?OH radicals and h⁺ had important roles in the photocatalytic degradation of methyl orange by TiO₂–SiO₂–NiFe₂O₄.     

Preparation and characterization of SO4 2−/Fe2O3–TiO2–Nd2O3 catalyst

This paper reports on the preparation of SO₄ ^2?/Fe₂O₃–TiO₂–Nd₂O₃ (SFTN) by combustion method. The effect of Nd content on catalytic activity was investigated. The prepared materials doped and undoped by Nd were compared by means of TG-DTG, XRD, FT-IR, NH₃-TPD and TEM techniques. Results indicated that the introduction of Nd improved the catalytic activities of the catalysts. Catalytic activity of SFTN was the highest with 98.3 % menthol conversion when Nd content was at 2 wt%. The introduction of Nd stabilized the coordination bond between the sulfate irons and the metallic oxides, helping in the formation of solid acid sites, enhancing the dispersion of catalyst particles, and inhibiting the growth of catalyst particles under heating.     

Synthesis of sulfonyl chlorides and thiosulfonates from H2O2–TiCl4

A new method is described for the oxidative chlorination of thiols to sulfonyl chlorides using titanium tetrachloride in combination with the oxidant hydrogen peroxide. Direct conversion of thiols into their corresponding thiosulfonates is also reported. Good to excellent yields, short reaction times, high efficiencies, cost-effectiveness, and, facile isolation of the desired products make the present methodology a practical alternative.     

Thermal Methods Applied to the Glass Transition of Mixed Network AlPO4–BPO4–SiO2 Glasses

Glass transition effect of mixed network AlPO₄–BPO₄–SiO₂ glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition effect has structurally sensitive properties. Glass transition temperature T _g, changes of specific heat (Δc _p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition effect. Its course is dependent on the flexibility of the structure of glasses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the Activity Coefficients of NaCl in the System NaCl–NH4Cl–H2O

Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl–NH₄Cl–H₂O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH₄Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH₄⁺ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg^-1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.     

Conductivity of Al2(WO4)3–WO3 and Al2(WO4)3–Al2O3 Composites

Russian Journal of Electrochemistry - Composites of (1 – x)Al2(WO4)3–xWO3 and (1 – x)Al2(WO4)3–xAl2O3 are synthesized and their conductivity is studied as dependent on the...     

Synthesis and photocatalytic properties of core–shell TiO~2@ZnIn_2S_4 photocatalyst

A novel core–shell TiO2@ZnIn2S4composite has been synthesized successfully by a simple and flexible hydrothermal route using TiO2as precursors.The as-synthesized samples were characterized by X-ray diffraction,UV–vis diffuse reflectance spectra and transmission electron microscopy.The photocatalytic properties of samples were tested by degradation of aqueous methylene blue（MB）under visible light irradiation.It was found that the as-synthesized TiO2@ZnIn2S4photocatalyst was more effcient than TiO2and ZnIn2S4in the photocatalytic degradation of MB.Moreover,TEM images confrmed the TiO2@ZnIn2S4nanoparticles possessed a well-proportioned core–shell morphology.     

Synthesis of the novel CuAl2O4–Al2O3–SiO2 nanocomposites for the removal of pollutant dye and antibacterial applications

Research on Chemical Intermediates - CuAl2O4–Al2O3–SiO2 nanocomposites with different amounts of CuAl2O4 (40, 50, 60 and 70 wt. %) were synthesized by the sol–gel method and...     

Phase Equilibria in the System NH4Al(SO4)2–H2SO4–H2O

Equilibrium solubility curves of the ammonium aluminium sulphate in aqueous solutions of sulphuric acid have been calculated using checked literature data and our own measurements. The concentration of sulphuric acid ranged from 0 to 23 mass%, temperature range between 20 and 60°C has been extrapolated up to 75°C by means of a thermodynamically based correlation method. The solubility correlation as well as the hydration analysis implied a possible destructuralization of solutions at higher acid concentrations. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the electrodialysis of aqueous H2SO4–CuSO4 electrolytes with metallic impurities

This work aims to contribute to the characterization of the electrodialysis (ED) of aqueous sulfuric acid–copper sulfate solutions. The presence of impurities such as As and Sb, typical of copper electrorefining electrolytes, is also studied. Results from kinetic studies carried out in ED cells with and without re-circulation are presented. The concentrations were: 3–9 g l⁻¹ copper, 50 g l⁻¹ sulfuric acid, 3 g l⁻¹ arsenic and 0.025 g l⁻¹ antimony; the temperatures, 22 and 44 °C; the transport rates, depending on experimental conditions, 0.2–0.6 mol h⁻¹ m⁻²of membrane for copper, 0.65–2.8 for sulfate, and 0.016–0.03 for arsenic. A speciation model has been developed and applied in order to interpret the experimental results and the performance of the studied cells has been evaluated. The main conclusion is that ED can be applied to the separation and concentration of chemical species in these systems.     

Adsorptive Voltammetric Measurement of Trace Level of Iron(III) with 4–(2–Pyridylazo) Resorcin

Abstract

The polarographic behavior of the complex of iron–4– (2–pyridylazo) resorcin(PAR) was studied. In HAc– NaAc– EDTA buffer solution, the complex can be adsorped on a hanging mercury drop electrode giving a sensitive adsorptive complex reduction peak with a peak potential at -0.36V(vs. SCE). Optimum experimental conditions were found by the use of 0.08mol/L HAc, 0.06mol/L NaAc, 5.0 × 10^?3mol/L EDTA and 1.0 × 10^?5mol/L PAR. With preconcentration for 60s, the derivative peak height of the complex compound is linearly proportional to the concentration for Fe in the range from 1.0 × 10^?9mol/L to 1.0 × 10^?7mol/L. For a 2–min pre–concentration time, the detection limit found was 2.0 × 10^?10mol/L. This method has high sensitivity and selectivity. It has been applied to the determination of trace iron in food and water samples without any pre–separation step.     

Radioluminescence of Europium(III) in POCl3–SnCl4–235UO2+ 2–Eu3+, and D2O–235UO2+ 2–Eu3+ Solutions

Results of studying the spectral and luminescent properties of Eu³⁺ ions upon homogeneous excitation of POCl₃–SnCl₄–^-UO²⁺ ₂–Eu³⁺ and D₂O–²³⁵UO²⁺ ₂–Eu³⁺ solutions by -particles are presented. It was found that the radioluminescence intensity of Eu³⁺ ions in both solvents increases proportionally to the energy input by -particles. The yield of radioluminescence photons from europium ions in the POCl₃–SnCl₄–UO²⁺ ₂–Eu³⁺ solutions is more than nine times as high as that in D₂O–UO²⁺ ₂–Eu³⁺. The radiation-chemical yields of excited ⁵ D ₀ states of Eu³⁺ ions are 0.74 ± 0.07 and 0.18 ± 0.02 ions/100 eV in POCl₃–SnCl₄–UO²⁺ ₂–Eu³⁺ and D₂O–UO²⁺ ₂–Eu³⁺ solutions, respectively.     

Synthesis and characterization of Na2O–CaO–SiO2 glass–ceramic

The Na₂O–CaO–SiO₂ ternary glass–ceramic with the composition of 49 mass% Na₂O, 20 mass% CaO, and 31 mass% SiO₂ was prepared by the conventional method. The ternary glass–ceramic was characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The Na₂CaSiO₄ phase, having the cubic crystal system, with the crystallite size of 25.14 nm and lattice parameter of 0.7506 nm was determined from the XRD pattern. The activation energy of the glass–ceramic calculated from the DTA curves was found to be 162.02 kJ mol^?1. The Avrami exponent was found to be ~2 indicating a one-dimensional growth process. The mass loss percent from ambient temperature to 1,173 K is less than 1 %. The density was calculated to be 2,723 kg m^?3. The fine-grained microstructure with the particle sizes less than 1 μm was confirmed by the scanning electron microscope micrograph.     

Phase analysis of the solidified KF–(LiF–NaF–UF4)–ZrF4 molten electrolytes for the electrowinning of uranium

The X-ray diffraction (XRD) phase analysis of different solidified uranium-based fluoride systems ((LiF–NaF)_eut–UF₄; (KF–LiF–NaF)_eut–UF₄; (LiF–NaF)_eut–UF₄–ZrF₄ and (KF–LiF–NaF)_eut–UF₄–ZrF₄) were examined in order to provide the basis for pyro-electrochemical extraction of uranium in molten fluorides. Several uranium-based species (Na₂UF₆, Na₃UF₇, K₂UF₆, K₃UF₇, UO₂, K₃UO₂F₅) were identified in the solidified melts. The role of oxygen in argon atmosphere was found to be critical in the formation of uranium species during the melting and solidification. In order to reduce the accumulated level of free oxygen traces in our experiments, zirconium (in the form of ZrF₄) was used inside the melt as an oxygen buffer. It was found that ZrF₄ can really stabilize the uranium species by complexation and protects them against the oxygenation. The results of this work highlight the importance of oxygen removal for obtaining pure deposit in the electrorefinning of uranium.     

Measurements of the Solid–Liquid Equilibria in the Quaternary System NaCl–NaBr–Na2SO4–H2O at 323 K

Phase equilibria of the quaternary NaCl–NaBr–Na₂SO₄–H₂O system at 323 K were studied by the isothermal dissolution equilibrium method. The solubilities of salts and densities of saturated solutions were determined. Solid solutions [Na(Cl, Br)] were found in the experiments. The phase diagram of the quaternary system has no invariant point, but has one univariant curve at the boundary of Na(Cl, Br) and Na₂SO₄ crystallization fields. The experimental results show that an increase of the NaBr concentration is accompanied by an obvious increase of the solution density and the decrease of the solubilities of NaCl and Na₂SO₄.     

Experimental Study on Phase Equilibria in Na2B4O7–Na2SO4–H2O and Li2B4O7–Na2B4O7–H2O Aqueous Ternary Systems at 273 K

Russian Journal of Physical Chemistry A - The solubility data for ternary systems Na2SO4–Na2B4O7–H2O and Li2B4O7–Na2B4O7–H2O at 273 K were obtained experimentally by the...