Study on phase diagrams and properties of solutions in ternary systems Li+,K+(Mg2+)/SO42--H2O at 25°C

Solubilities of ternary systems Li⁺,K⁺/SO^2-₄-H₂O (1) and Li⁺,Mg²⁺/SO₄^2--H₂O (2) were investigated by isothermal method at 25°C. Physico-chemical properties of solutions, such as density, refractive index, viscosity, conductivity and pH, were determined. Phase diagram of the system (1) consists of three solubility branches and three crystallization fields corresponding to K₂SO₄, Li₂SO₄·H₂O and LiKSO₄. LiKSO₄ is an incongruent compound, and its transition point is estimated graphically to be 45.5–46.0°C. No solid solution of LiKSO₄ with Li₂SO₄·H₂O was found in the system. The system (2) is a simple eutonic type. Pitzer model of electrolyte solution was used to check the obtained solubilities. Data comparison gives good agreement. Two equations were used to correlate density, refractive index of the solution with its composition. Differences between measured and calculated values are less than 0.6% for density, 0.15% for the latter.     

Thermodynamics of phase equilibria of the K2SO4 +Rb2SO4+H2O system at 25°C

Activities of water in the K₂SO₄+Rb₂SO₄+H₂O system at 25°C have been measured isopiestically. On the basis of the experimental activities of water ternary parameters of the Pitzer equations have been calculated. According to our data and experimental solubility data from the literature, continous solid solutions between K₂SO₄ and Rb₂SO₄ are formed in this system. With the use of the Guggenheim polynomial for simulating excess functions of solid solutions on the basis of the original and literature solubility data, excess Gibbs energies of solid solution formation as well as a solubility diagram have been calculated. Results of the solubility calculation are in good agreement with experimental data.     

Mechanism for nucleation and growth of electrochemical palladium deposition on an Au(111) electrode

The initial kinetics of electrochemical deposition of palladium on an Au(111) electrode in 0.1 M H₂SO₄ solution containing K₂PdCl₄ have been investigated quantitatively by cyclic voltammetry (CV) and potentiostatic current transient measurements. A cathodic current maximum was observed in the initial stage of Pd deposition process in 0.1 mM K₂PdCl₄ solution. The analysis shows that the deposition of palladium in this solution proceeds by an instantaneous nucleation and two-dimensional (2D) growth mode. When the concentration of K₂PdCl₄ became higher, a potential-dependent cathodic current ‘plateau’ after the current maximum was observed. Simple nucleation-growth models cannot fit the transients in the region of the ‘current plateau’. The present current transient results were discussed in comparison with the results obtained by in situ scanning tunneling microscopy (STM).     

Solubility in K+-Na+-Mg 4 2− aqueous solution at T = 298.15 K

In the salt solubility predictions for K⁺-Na⁺-Mg ₄ ^2? aqueous solution the treatment of thermodynamic data of three-component systems at T = 298.15 K involved the application of the Extended Pitzer’s ion-interaction model for the pure and mixed electrolyte solutions and criteria of phase equilibrium. Osmotic coefficients data of three-component systems were revised according to recently published parameters of the solutions NaCl(aq) and KCl(aq) that served as reference standards in isopiestic measurements. Parameters of the extended ion-interaction model of K₂SO₄(aq) are determined by treatment of experimental and predicted values of osmotic coefficient in supersaturated region obtained by the Zdanovskii-Stokes-Robinson rule. Results of salt solubility prediction were compared to experimental solubility data from literature. The agreement between calculated and experimental solubility data in the systems K₂SO₄ + MgSO₄ + H₂O, Na₂SO₄ + MgSO₄ + H₂O, and Na₂SO₄ + K₂SO₄ + H₂O at T = 298.15 K, was excellent.     

Studies on the electrochemical characteristics of K2Sr(FeO4)2 electrode

K₂Sr(FeO₄)₂ was prepared from K₂FeO₄ and characterized by SEM, XRD, IR and AAS. The measured solubility of K₂Sr(FeO₄)₂ is lower than that of K₂FeO₄ either in various concentrations of aqueous potassium hydroxide at room temperature (25 °C) or in saturated KOH solution at different temperatures. Discharge performance of K₂Sr(FeO₄)₂ electrode under different conditions was studied by the constant current discharge method. The discharge efficiency of K₂Sr(FeO₄)₂ electrode is higher than that of K₂FeO₄ electrode at the same discharge condition. The electrochemical characteristics of K₂Sr(FeO₄)₂ electrode were also investigated by means of electrochemical impedance spectroscopy (EIS).     

Metastable phase equilibria for the ternary aqueous system of lithium sulfate and potassium sulfate at <Emphasis Type="Italic">T</Emphasis> = 308.15 K: Experimental data and prediction using Pitzer model

The metastable solubilities and the physicochemical properties including density, refractive index, pH and conductivity in the ternary system (Li₂SO₄ + K₂SO₄ + H₂O) at T = 308.15 K were determined experimentally using the isothermal evaporation method, and the metastable phase diagram and the physicochemical properties versus composition diagram were plotted. In the metastable phase diagram, there are two invariant points, three univariant curves and three crystallization regions corresponding to lithium sulfate monohydrate (Li₂SO₄ · H₂O), double salt (K₂SO₄ · Li₂SO₄) and arcanite (K₂SO₄). It was found that the double salt of K₂SO₄·Li₂SO₄ belongs to the incongruent double salt, and the hydrate of Li₂SO₄ · H₂O belongs to hydrate type I. On the basis of Pitzer model of the electrolyte solution theory, the mixing-ion parameter of θ_Li,K, \({\Psi _{Li,K,S{O_4}}}\) and the metastable equilibrium constants of the solid phases K₂SO₄, Li₂SO₄ · K2SO4 and Li₂-SO₄ · H₂O at 308.15 K were obtained for the first time. The calculated metastable solubility data for this ternary system at 308.15 K agree well with the experimental values, and this result indicates that the mixing-ion parameters and the metastable equilibrium constants obtained in this work are reliable.     

Studies on the influence of various experimental conditions on electrochemical generation of ferrate(VI) in NaOH-KOH mixed electrolyte

Ferrate(VI) was prepared by electrooxidation in diaphragm electrolyzer with iron wire gauze as anode and NaOH-KOH mixed solution as electrolyte. The influences of various experimental conditions, such as the volume ratio of NaOH-KOH mixed electrolyte, temperature, current density, passivation of iron anode were investigated on ferrate current efficiency. Due to the low solubility of K₂FeO₄ in concentrated alkaline solution and the passivation of iron wire gauze anode, a highest current efficiency over 90% was obtained at 45°C and at a current density of 5 mA cm⁻² in mixed electrolyte with the volume ratio of NaOH: KOH equal to 6: 4. The result is superior to using NaOH and KOH as electrolyte respectively. In addition, polarization curves, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were employed to further study the effects of synthesis conditions on ferrate(VI) in theory. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 853–857. The article is published in the original.     

In-situ electrochemical study of chalcopyrite pressure oxidation leaching from 110 °C to 150 °C under saturated vapor pressure

Pressure oxidation leaching behavior of chalcopyrite in sulfuric acid solution from 110 °C to 150 °C were investigated by in-situ electrochemical methods. Leaching experiments under saturated vapor pressure conditions were used to simulate the anoxic environment that may be encountered in industrial applications. Scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the morphology and the chemical status of chalcopyrite surface. Results show that the copper extraction was increased with the increase of leaching temperature. Under the optimal leaching conditions under saturated vapor pressure, the copper and iron extraction are 8.3% and 29.8%, respectively. When the temperature increased from 110 °C to 150 °C, the self-corrosion potential and electrochemical reaction resistance firstly increased and then decreased. In contrast, the resistance of the passive film was always increased with the increase of temperature. The electrochemical study results indicated that the increase in temperature affected the oxidation of chalcopyrite by altering the kinetics of the cathodic reaction and the anodic passivation. Both the self-corrosion current density (i_corr) and rate constant were affected by the reduction of Fe(III). The XPS results show that elemental sulfur and H₃O(Fe₃(SO₄)₂(OH)₆) were the main leaching solid products. The formation of H₃O(Fe₃(SO₄)₂(OH)₆) not only caused a decrease in cathodic reaction kinetics, but also increased the resistance of mass transfer process. Due to the faster release of iron, copper-rich sulphides were formed, which mixed with the elemental sulfur and/or H₃O(Fe₃(SO₄)₂(OH)₆) led to coverage of the chalcopyrite surface.     

Structure and proton-donating ability of trifluoro-<Emphasis Type="Italic">N</Emphasis>-(2-phenylacetyl)methanesulfonamide

According to the data of quantum-chemical calculations and IR spectroscopy the trifluoro-N-(2-phenylacetyl)methanesulfonamide CF₃SO₂NHC(O)CH₂Ph in the isolated state and in inert media exists in the form of two conformers with the syn- and antiperiplanar orientation of the C=O and N-H bonds. Its self-associates in the CCl₄ solution and in molecular crystals constitute cyclic dimers formed by the NH···O=S bonds and chain dimers with the NH···O=C bonds. As a hydrogen bond donor, trifluoro-N-(2-phenylacetyl)methanesulfonamide is stronger than N-methyltrifluoromethanesulfonamide. Its pK _a in methanol is 5.45, that is 5 pK units lower than for amides CF₃SO₂NHR and 2 pK units higher than for imide (CF₃SO₂)₂NH.     

A new simple preparation of platinum-nickel alloy nanoparticles and their characterization as an electrocatalyst for methanol oxidation

Pt-Ni alloy nanoparticles were produced by casting 2 or 10 mM H₂PtCl₆ solutions on a Ni column. The apparent particle size for the resultant Pt-Ni alloys increased with the concentration of the H₂PtCl₆ solution, while the content of Pt in the alloy decreased. The potential sweeps of 5 cycles in an H₂SO₄ aqueous solution for Pt-Ni (2 mM)/Ni and Pt-Ni (10 mM)/Ni electrodes led to electrochemical behavior similar to a polycrystalline Pt electrode, suggesting the formation of a few thin Pt layers on each Pt-Ni alloy surface. In electrochemical measurements, both Pt-Ni/Ni electrodes showed more negative onset potential of methanol oxidation and slower degradation of oxidation current of methanol than the polycrystalline Pt electrode. X-ray photoelectron spectroscopy of both Pt-Ni/Ni electrodes showed the shift of Pt4f peaks to a higher binding energy, suggesting that the increase in the d vacancy in the balance band 5d orbital of Pt contributed to the improved electrocatalytic activity and durability of the Pt-Ni/Ni electrodes.     

V2O5·0.6H2O nanoribbons as cathode material for asymmetric supercapacitor in K2SO4 solution

V₂O₅·0.6H₂O nanoribbons were prepared and their electrochemical behaviors in K₂SO₄ aqueous solution were investigated. Results show for the first time that K⁺ ions could intercalate/deintercalate reversibly in the V₂O₅·0.6H₂O lattice. An asymmetric supercapacitor activated carbon/0.5 mol/l K₂SO₄/V₂O₅·0.6H₂O was successfully assembled, which could be cycled reversibly in the voltage region of 0–1.8 V. This supercapacitor presents an energy density of 29.0 Wh/kg based on the total mass of the active electrode materials, a very good rate behavior with energy density of 20.3 Wh/kg at power density of 2 kW/kg, and also a rather good cycling performance.     

Solid–liquid phase equilibria in the system K2SO4–MnSO4–H2O at 298 K and 313 K

Phase equilibria studies of the system K₂SO₄–MnSO₄–H₂O published revealed discrepancies between the data presented in the literature regarding the solid phases formed at ambient temperatures. The solubility in the system at 298 K and 313 K was determined. At 298 K, the existence of the double salt K₂SO₄·3MnSO₄·5H₂O and of MnSO₄·H₂O was confirmed. The examinations at 313 K showed the formation of the stable solid phases MnSO₄·H₂O, K₂SO₄·2MnSO₄, K₂SO₄·MnSO₄·1.5H₂O, K₂SO₄ and the formation of a metastable phase K₂SO₄·MnSO₄·2H₂O.     

V2O5/赤铁矿催化剂结构及其NH3选择性催化还原NOx性能

以水热合成针铁矿为前驱体浸渍偏钒酸铵,分别于300,400和500℃空气中焙烧,制备了不同活性组分负载量的V₂O₅/赤铁矿（V/H）催化剂,用于氨选择性催化还原（SCR）脱硝。采用X射线衍射、透射电子显微镜、比表面积分析仪、程序升温还原及程序升温脱附等方法对催化剂结构进行了表征,并用标气配制模拟烟气进行了脱硝实验。结果表明,300℃煅烧3%V/H催化剂当烟气温度为250-300℃时NO转化率均可达95%以上;当配气中单独加入水蒸气或低浓度SO₂（0.01%）时,V/H催化脱硝的活性不受影响;当系统加入高浓度的SO₂（0.03%与0.05%）或同时添加H₂O与SO₂时,SCR脱硝效率下降,其机制可能是SO₂在催化剂表面竞争吸附所致,停止添加后,催化活性迅速恢复。     

Solid–liquid phase equilibria in the systems K2SO4–MSO4–H2O (M = Co,Ni, Cu) from ambient to enhanced temperatures

Reviewing the literature solubility isotherms in the ternary systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu, Zn) revealed a lack at ambient temperatures. The solid–liquid phase equilibria have been determined in the systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu) at T = 313 K. With increasing bivalent metal sulfate concentration, the solubility of potassium sulfate rises until the two-salt point is reached. Reciprocally, the solubility of the bivalent metal sulfate hydrates (CoSO₄·7H₂O, α-NiSO₄·6H₂O, CuSO₄·5H₂O) increases with rising potassium sulfate concentration. In all three systems the double salts of Tutton's type K₂SO₄·MSO₄·6H₂O (M = Co, Ni, Cu) are formed.     

Synthesis of Poly(<Emphasis Type="Italic">o</Emphasis>-anisidine)/H<Subscript>2</Subscript>SO<Subscript>4</Subscript> Film for the Development of Glucose Biosensor

The poly(o-anisidine)–sulfuric acid–glucose oxidase (POA–H₂SO₄–GOx) electrode has been investigated in the present work. Platinum electrode was used for the synthesis of poly (o-anisidine)–sulfuric acid (POA–H₂SO₄) film using galvanostatic method with 0.2 M o-anisidine, 1.0 M H₂SO₄ solution, 1.0 pH and 2 mA/cm² applied current density. The synthesized film was characterized using electrochemical technique, conductivity measurement, UV–visible spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. GO_X was immobilized on synthesized POA–H₂SO₄ film by cross-linking via glutaraldehyde in phosphate and acetate buffer. The Michaelis–Menten constant ( K_\textm￠K_{\text{m}}^\prime ) was determined for the immobilized enzyme. The glucose oxidase electrode shows the maximum current response at pH 5.5 and potential 0.6 V. The sensitivity of POA–H₂SO₄–GO_X electrode in phosphate and acetate buffer has been recorded. The results of this study reveal that the phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements.     

Solubility study of sodium, potassium and calcium sulfates and chlorides, in ammonia

Solubility of sodium, potassium and calcium sulfates and chlorides in 28% ammonia solution was determined through monitoring conductivity measurements and kinetics of solids dissolution as a function of temperature and stirring time. The major findings of the present study show that Na₂SO₄ and K₂SO₄ solutions conductivity follow straight linear segments with different slopes. However, in case of NaCl, KC1, CaCl₂ and CaSO₄ · 2H₂O, conductivity curves were continuous, monotonous and reach constants maximum values. The hypothesis of complex formation or dissolution via intermediaries such as NaNH₄SO₄ and KNH₄SO₄ salts seams to be true, through X-ray diffraction study of resulting deposits. Furthermore, the dissolution rates at 25°C of potassium and calcium chlorides in ammonia solution are higher than that reported in the literature for water. In fact, ammonia significantly reduces the solubility of K₂SO₄; conversely, a slight increase in this parameter was observed for CaSO₄.     

Electrochemical impedance spectroscopy study of cuprous oxide films formed on copper: effect of pH and sulfate and carbonate ions

The semiconducting properties of anodic passive films formed potentiostatically on polycrystalline copper in aqueous borax solutions were studied using electrochemical impedance spectroscopy, photocurrent spectroscopy and ellipsometric measurements. The semiconducting nature of the cuprous passive layer was analysed as a function of pH (9.2>pH>7.4), electrode potential and with the addition of 3.5 mM Na₂CO₃ and 8 mM Na₂SO₄. The different growth conditions change the compactness and the defect or excess of cations accumulated in the compact inner cuprous layer, leading to different semiconducting properties. Electronic Publication     

Solid–liquid phase equilibria in the system K2SO4–MgSO4–H2O at 318 K

The polythermal solubility diagram of the system K₂SO₄–MgSO₄–H₂O presents the formation of three double salts, picromerite, leonite, langbeinite appearing in this order with increasing temperature. In the temperature range between 314.15 K and 320.65 K, picromerite and leonite ought to coexist. The search in the literature revealed a lack of isothermal phase equilibrium data within this temperature range. Therefore, the solubility in the system K₂SO₄–MgSO₄–H₂O was determined in the whole concentration range at 318 K. The solid phases, epsomite, leonite, picromerite and arcanite occur with increasing potassium sulfate concentration. A two-salt point of leonite and picromerite is established at 0.618 molal K₂SO₄ and 3.030 molal MgSO₄ at the temperature of investigation.     

Formation of peracids from corresponding organic acids under oxygen electroreduction in gas-diffusion electrode

The effect of conditions of electrolysis in aqueous solutions of (K₂SO₄ + H₂SO₄) electrolytes was studied in the presence of formic, acetic, and butyric acids on the formation of the corresponding peracids under oxygen electroreduction in carbon black gas-diffusion electrodes. In the presence of organic acids with the concentration of 1.5–4.7 M, as dependent in the electrolysis conditions, the current efficiency of H₂O₂ formation decreases from 70 to 13 % and its concentration drops from 2.3 to 0.4 M. Electrolysis under constant current (50–100 mA/cm²) results in formation of peracids with the concentration of up to 7.5 mM. No direct dependence of the concentration of peracids on the concentration of the obtained H₂O₂ is observed. The presence of tetrabutylammonium bromide in the solution inhibits significantly peracid formation. It is assumed that synthesis of peracids occurs partly on the surface of carbon black through activation of the adsorbed acid by a hydrogen cation and further interaction with the active form of oxygen obtained under oxygen reduction or decomposition of H₂O₂.     

Untersuchungen an Systemen aus Salzen und gemischten Lösungsmitteln. VI. Das Verhalten des reziproken Salzpaares Na2SO4 + 2 KCl ⇌ K2SO4+2 NaCl in Methanol-Wasser-Mischungen

The solubility isotherms of the system Na₂SO₄? K₂SO₄? CH₃OH? H₂O at 25,40 and 55°C and the solubilities in the system of the metathetic salt reaction Na₂SO₄+ + 2KCl ? K₂SO₄ + 2NaCl in methanol-water mixtures at 10 and 25°C have been determined and the nature of the solid phases established. The addition of methanol causes an enlargement of the sulphatic existence fields. A flow sheet for the industrial application of the results is communicated.