Electrochemical properties of Pb–Sb, Pb–Ca–Sn and Pb–Co3O4 anodes in copper electrowinning

Three types of anode, Pb–Sb, Pb–Ca–Sn and Pb–Co₃O₄, for copper electrowinning were investigated. The corrosion resistance, as evaluated by cyclic voltammetric (CV) measurements was higher for Pb–Co₃O₄ than for Pb–Sb and Pb–Ca–Sn. During prolonged electrowinning under galvanostatic conditions, the anodic reaction on the Pb–Co₃O₄ anode was depolarized by 0.053 V as compared to Pb–Sb, and by 0.106 V with respect to Pb–Ca–Sn. The composition and structure of the anodic layer were determined by XPS, X-ray and SEM analyses. The surface layer on the three anodes examined was composed mainly of PbSO₄, -PbO₂ and -PbO₂. Different structure of the surface layer was observed: loose and highly spread coral-like structure in the case of Pb–Sb; fibrous structure in the case of Pb–Ca–Sn and dense, fine-grained structure in the case of Pb–Co₃O₄.     

Polymer-Salt Synthesis of Photoactive Bactericide ZnO–Ag and ZnO–SnO2–Ag Nanopowders and a Study of Their Structure and Properties

Glass Physics and Chemistry - This paper describes the low-temperature polymer-salt synthesis of ZnO–Ag nanopowders and presents the results of studying their structure, morphology, and...     

Study of the Selectivity of Binary Agents by Gas–Liquid Chromatography

Theoretical Foundations of Chemical Engineering - The selective properties of individual and binary agents are compared according to data obtained by gas–liquid chromatography (GLC). The...     

Study of Synthesis and Evaluation of Heat-Resistant Coatings Based on Silicon–Boron Carbide–Zirconium Boride–Aluminum Oxide Composite

The effect of nanosized fibers of aluminum oxide on the properties of protective coatings based on the silicon–boron carbide–zirconium boride composite is investigated. The coatings applied on different substrates (graphite and ceramics) are compared and the effect of the thermal treatment conditions on the formed coatings is examined. It is demonstrated that the introduced additives do not weaken the coating’s thermal resistance and allow reducing the cost of the coating, darkening the color, and protecting it from erosion.     

Electrochemical properties of electrodeposited nanocrystalline cobalt and cobalt–iron alloys in acidic and alkaline solutions

Nanocrystalline Co and CoFe with varied iron contents ranging from 5 to 25 wt% Fe were electrodeposited from a sulfate bath. The average grain sizes of the coatings obtained were measured using Scherrer equation and calculated to be in between 16 and 65 nm. Electrochemical corrosion behavior of electrodeposited nanocrystalline cobalt (Co) and cobalt–iron (CoFe) alloys was investigated in both acidic (0.1 M H₂SO₄) and alkaline solution (0.1 M NaOH). This study investigates the corrosion behavior of electrodeposited CoFe alloy coatings using polarization tests, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy techniques. The nanocrystalline Co and CoFe showed active behavior for all alloy coatings in acidic condition, while an active–passive–transpassive behavior was seen for all coatings in alkaline condition.     

Electrochemical investigation of the roles of oxyanions in chemical–mechanical planarization of tantalum and tantalum nitride

Nitrate, sulfate, and phosphate oxyanions are shown to serve as effective surface-modifying agents for low-pressure chemical–mechanical planarization (CMP) of Ta and TaN barrier layers of interconnect structures. The surface reactions that form the basis of this CMP strategy are investigated using cyclic voltammetry, open circuit potential and polarization resistance measurements, and impedance spectroscopy. The results suggest that forming structurally weak layers of surface oxides is crucial to chemically controlling the CMP of Ta/TaN at low polish-pressures. It is shown that in oxyanion-based slurries, this can be accomplished by modifying the sample surfaces with anion-incorporated oxide films of Ta or TaN, which, in turn, can readily be removed with moderate abrasion. Electrochemical results elaborate the reaction mechanisms that lead to anion-modified oxides, such as Ta₂O_5(1−x)(NO₃)_10x , Ta₂O_5(1−x)(SO₄)_5x , and Ta₂O_5(1−x)(PO₄)_10x/3 on both Ta and TaN surfaces in pH-controlled solutions of KNO₃, K₂SO₄, and KH₂PO₄ solutions, respectively.     

Synergism and Performance Optimization in Liquid Detergents Containing Binary Mixtures of Anionic–Nonionic, and Anionic–Cationic Surfactants

In this paper evaluation of surface active and application properties in liquid detergent formulations containing binary mixtures of anionic–nonionic, and anionic–cationic surfactants is discussed. Surfactants used include: linear alkylbenzene sulfonate (LAS), alcohol ether sulfate (AES-2EO), alcohol ethoxylate (AE-7EO), lauryl dimethyl amine oxide, and alkyl hydroxyethyl dimethyl ammonium chloride (AHDAC). Surface active parameters relating to the effectiveness and efficiency of surface tension reduction were determined from the surface tension data. Non-ideal solution theory was used to determine the degree of interactions between the two surfactants, and the conditions under which a mixture of two surfactants show synergism in surface active properties. Our data indicated that synergism in mixed surfactants increases with the degree of charge difference between the surfactants. In both mixed micelle and mixed monolayer formation, the degree of interactions between the two surfactants in the mixture increased in the following order: LAS/AE < AES-2EO/amine oxide < AES-2EO/AHDAC. This synergistic behavior as presented in this paper leads to unique application properties and improved performance in terms of foam volume, and soil removal which has applications in formulation of dishwashing liquids, and laundry detergents.     

Thiazolidinediones: An In–Depth Study of Their Synthesis and Application to Medicinal Chemistry in the Treatment of Diabetes Mellitus

2,4-Thiazolidinedione (TZD) is a privileged and highly utilised scaffold for the development of pharmaceutically active compounds. This sulfur-containing heterocycle is a versatile pharmacophore that confers a diverse range of pharmacological activities. TZD has been shown to exhibit biological action towards a vast range of targets interesting to medicinal chemists. In this review, we attempt to provide insight into both the historical conventional and the use of novel methodologies to synthesise the TZD core framework. Further to this, synthetic procedures utilised to substitute the TZD molecule at the activated methylene C₅ and N₃ position are reviewed. Finally, research into developing clinical agents, which act as modulators of peroxisome proliferator-activated receptors gamma (PPARγ), protein tyrosine phosphatase 1B (PTP1B) and aldose reductase 2 (ALR2), are discussed. These are the three most targeted receptors for the treatment of diabetes mellitus (DM).     

Electrochemical fabrication of Rh–Pd particles and electrocatalytic applications

Electrochemical deposition method was employed for the fabrication of rhodium–palladium (Rh–Pd) particles on the glassy carbon electrode (GCE) and indium tin oxide (ITO) electrode surface. Surface morphological analysis of Rh–Pd film has been carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Here, the electrodeposited Rh–Pd particles were found in the average size range of 30–200 nm. The electrochemical activities of the Rh–Pd film have been investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopic (EIS) analysis. The Rh–Pd particles-modified GCE successfully detects the hydrogen peroxide (H₂O₂) (in pH 7.0 phosphate buffer solution (PBS)) in the linear range in the lab (10–460 μM) and real samples (10–340 μM). The Rh–Pd particles-modified GCE possesses the good sensitivity and selectivity for the detection of H₂O₂ in lab and real samples.     

Study of the Behavior of Mo40Si40B20 Coatings in the Temperature Range of 1000–1200°С

Glass Physics and Chemistry - The resistance of Mo40Si40B20 magnetron coatings to high-temperature oxidation in the 1000–1200°С temperature range is investigated. The main phases...     

Electrochemical deposition of zinc–polystyrene composites in the presence of surfactants

The electrochemical codeposition of polystyrene particles and zinc on a rotating cylinder electrode was investigated. Rheological measurements indicate strong aggregation of the PS particles in the zinc deposition electrolyte. Addition of cetylpyridinium chloride, a cationic surfactant, prevents aggregation and enhances polystyrene codeposition. Other surfactants also increase suspension stability, but diminish polystyrene codeposition, irrespective of their charge. Hence, the surfactant charge does not affect polystyrene codeposition. The variation of polystyrene incorporation with the amount of suspended polystyrene, current density and electrode rotation speed signifies that polystyrene codeposition with zinc is determined by the competition between particle removal forces and particle adhesion forces at the cathode surface. The effect of the surfactants can be related to changes in surface roughness of zinc due to surfactant adsorbed on the electrode. Cetylpyridinium chloride behaves differently from the other surfactants, because it is reduced at the cathode.     

Behaviour of Nafion® 350 membrane in sodium sulfate electrochemical splitting: continuous process modelling and pilot scale tests

A two-compartment membrane electrolysis cell is used to split sodium sulfate into sulfuric acid and sodium hydroxide. The cell is equipped with a Nafion® 350 cation-exchange membrane. Due to the dissociation of the strong acid, free hydrogen ions migrate through the membrane together with sodium ions. This transfer decreases current efficiency. The transport properties of Nafion® 350 membrane are studied in a laboratory cell. Current efficiency varies either with sulfuric acid to total sulfate concentration ratio in the anolyte or with sodium hydroxide concentration depending on the membrane state. Water transport through the membrane is due to electroosmosis. Hydrogen and sodium ions carry three to four molecules of water per ion. Modelling of a continuous feed and bleed process in the steady-state is performed using material balance and transport data obtained in a laboratory scale. Tests in a pilot plant (scaling factor 13) were undertaken. The model predictions agree well with experimental results. As a consequence, the model may be used for industrial purposes. Due to current efficiency decrease when salt conversion increases, the use of a cascade of cells in series is advantageous compared to a single stage.     

Electronic Polarizability of Vitreous Alloys in the Ge–As–S System

The influence of temperature on the electronic polarizability of vitreous alloys along the (As₂S₃)_x· (GeS₂)_{1 – x}(0 < x< 1) join in the Ge–As–S system is investigated. Numerical values of the coefficients in the expression describing the temperature dependence of the electronic polarizability are determined. It is found that the temperature change in the polarizability with a variation in the composition is governed by the ratio of two contributions, namely, the change in polarizability unrelated to changes in the density and the photoelastic effect.     

An Electrochemical study of the formation of Benzotriazole surface films on Copper, Zinc and a Copper–Zinc alloy

The electrochemical behaviour of Cu, Cu–37Zn and Zn in benzotriazole (BTA) containing chloride solutions was studied and compared using potentiodynamic, cyclic voltammetry and electrochemical impedance spectroscopy. The presence of BTA in the chloride-containing solutions gave rise to higher breakdown potentials, significantly higher polarisation resistances and inhibited the formation of CuCl₂ and zinc-containing corrosion products. These effects were observed for pure Cu, Cu–Zn and to a somewhat lesser extent pure Zn. The electrochemical impedance data were consistent with the formation of a polymeric BTA-containing layer for all three systems.     

Anodic Oxidation of Nitric Oxide on Au/Nafion®: Kinetics and Mass Transfer

The rate determining step for the anodic oxidation of nitric oxide on Au/Nafion^® was experimentally and theoretically found to beNO + Au Au–NO_ads The anodic oxidation of nitric oxide was first order with respect to nitric oxide. The reaction rate constant increased from 3.3×10^–5 to 9.6×10^–5cm s^–1 as the applied potential increased from 0.74 to 0.77V. The anodic oxidation of nitric oxide was controlled by the electrochemical kinetics when the anodic potential was less than 0.8 V. When the potential was greater than 1.0 V, it was located in the mass transfer region. The limiting current increased from 1184 to 1589A with increase in gas flow rate from 250 to 750ml min^–1 when the potential was set at 1.05 V and the concentration of nitric oxide was 100 ppm. The diffusion resistance in the gas diffusion layer can be neglected for gas flow rates greater than 750 ml min^–1. The diffusivity of nitric oxide and the equivalent diffusion layer thickness within the porous electrode were evaluated to be 3.43×10^–4cm²s^–1 and 0.051 cm, respectively.     

Fabrication and application of Nafion®-modified boron-doped diamond electrode as sensor for detecting caffeine

The surface of boron-doped diamond (BDD) electrodes has been modified by Nafion^®. The polymer film was applied onto the BDD electrode surface by solvent evaporation. Nafion^®-BDD electrode was used as a sensor for caffeine detection in e.g. cola beverage samples. In cyclic voltammetric measurements, favorable ionic interaction between the Nafion^® film and caffeine enhances the current response, and thus the sensitivity, compared to that at the bare electrode. The modified electrode exhibits a stable and sensitive response to caffeine and may represent a new analytical tool, offering a significant improvement over other electroanalytical methods (e.g.: Nafion^®-modified glassy carbon electrode) and the accepted method for caffeine analysis (HPLC-MS). The analysis of residuals from the linear regression proved that a linear response exists from 2.0 × 10^? 7 to 1.2 × 10^? 5 M, obtaining a limit of detection of about 1.0 × 10^? 7 M. The findings presented in this study are described and discussed in the light of the existing literature.     

AFM and XPS Study of the Sintering of Realistic Ag/{0001}α-Al2O3 Model Catalysts Under Conditions of Ethene Epoxidation

The stability under reaction conditions of realistic Ag/-alumina model catalysts prepared by an appropriate wet chemical route has been studied by AFM and XPS. Although thermal and oxygen-induced sintering of Ag particles on {0001}-alumina are significant, parts per million levels of dichloroethane have a much larger effect. It is suggested that this latter effect is due to AgCl-mediated intra-particle transport of silver. Such chlorine-induced sintering is likely to be the principal cause of the loss of Ag metal area under industrial conditions.     

Experiments and Correlations of the Solubility of γ-DL-Methionine in Binary Solvent Mixtures

Antisolvents increase the supersaturation in the crystallization process which can enhance the product yield. The effect of an antisolvent on the solubility of γ-DL-methionine (γ-DL-met) in aqueous solution was investigated. The solubility of γ-DL-met was measured with various binary solvent mixtures. It improved with higher temperature but decreased with increasing the antisolvent mass fraction. Acetone showed the highest efficiency to reduce the solubility. The solubilities were correlated with the van't Hoff-Jouyban-Acree model and the modified Apelblat-Jouyban-Acree model. Both models fitted to the experimental results with high accuracy. Enthalpy, entropy, and Gibbs free energy of dissolution were determined by van't Hoff analysis. The thermodynamic properties indicated that the dissolution process is endothermic and entropy-driven.     

Electrochemical behaviour of LaCl3 at tungsten and aluminium cathodes in LiCl–KCl eutectic melt

The electrochemical behaviour of lanthanum was studied at inert tungsten electrode and reactive aluminium electrode in LiCl–KCl eutectic melt in the temperature range 698–798 K using transient electrochemical techniques. Reduction of La(III) to La(0) at the tungsten electrode takes place in a single step. The reduction shows quasi-reversible behaviour for polarization rates, 25 ≤ ν ≤ 150 mV s^?1 and is predominantly controlled by charge transfer of La(III) ions for scan rates higher than 75 mV s^?1. The heterogenous rate constant of the process was estimated from impedance spectroscopy and from the semi-integrals of the cyclic voltammograms. The redox potential of the La(III)/La couple at the Al electrode was observed to be more positive than that at the inert electrode. This potential shift is due to the lowering of the activity of La in the metal phase caused by the formation of the intermetallic compound Al₁₁La₃. Thermodynamic properties such as Gibbs energy of formation of Al₁₁La₃, excess Gibbs energy and the activity coefficient of La in Al were calculated from the open circuit potential measurement.     

Electrochemical reduction of solutions of ReF6 in fused LiF–NaF–KF eutectic mixture

Electrolyte was prepared by introducing gaseous ReF₆ into the molten LiF–NaF–KF eutectic at 600 °C. The electrochemical properties of the solutions were studied by voltammetric techniques. The reduction of ReF₈ ^2– to Re occurred via a single irreversible step with diffusion controlled mass transfer. The diffusion coefficient of ReF₈ ^2– was 8 × 10^–10 m² s^–1 and the cathodic transfer coefficient was 0.13. Well-crystallized pure rhenium layers, up to 50 m thick, were obtained on W, Ag, graphite and vitreous carbon substrates and were examined by SEM and X-ray diffraction techniques.