An investigation of the spouted bed electrode cell for the electrowinning of metal from dilute solutions

The depletion process of copper ions from dilute solutions has been used as a model system to investigate the spouted bed cell with a three-dimensional electrode of conducting particles. Experiments under potentiostatic and galvanostatic conditions have been carried out. Results obtained indicate that the spouted bed cell has several favourable characteristics for application in metal recovery. The potentiostatic mode of operation appears to be superior to the galvanostatic mode for electrowinning.     

Controlled stripping of aluminide coatings on nickel superalloys through electrolytic techniques

Aluminide diffusion coatings are widely employed to improve the oxidation and/or the corrosion resistance of highly added value turbine components operating in harsh environments at high temperatures. Refurbishment of such components requires appropriate removal of worn coatings and of the corrosion products layer—usually an oxide scale. Stripping is mostly carried out using hazardous chemical baths of limited reliability. In this work, an alternative stripping method based on electrochemical techniques has been carried out at laboratory scale for CVD Al diffusion coatings on a directionally solidified Ni base superalloy. Both the galvanostatic and the potentiostatic modes have been investigated. Prior to them, in situ gas bubbling induced by cathodic polarization seems to be an effective way to remove the superficial oxide scales. Measuring the open circuit potential during the experiments allows easy monitoring of the progress of the selective dissolution of the different layers. Complete removal of the aluminide coatings is indicated by potential values similar to those of the substrate. The correlation between the electrochemical features and the surface state after stripping has been carried out by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The electrochemical approach is a promising means to strip out surfaces in a selective and reliable manner.     

Mn掺杂ZnCo2O4纳米片阵列的制备及电化学性能研究

通过水热合成再煅烧的方法在泡沫镍表面生长出了Mn掺杂的ZnCo2O4纳米片阵列。利用XRD、SEM、EDS-面扫描、XPS对样品的结构/形貌和掺入的Mn元素的分布情况进行了表征。然后,再进一步对样品进行了循环伏安曲线、恒电流充放电和循环稳定性的测试。结果表明,样品在电流密度为3 mA/cm2时,比电容达到了2 134.1 F/g;在电流密度为10 mA/cm2时,循环1 000圈,电容保持率为98.59%。因此,合成的样品比电容较高且循环稳定,是一种较为理想的超级电容器的电极材料。     

The comparison of galvanostatic and potentiostatic copper powder deposition on platinum and aluminium electrodes

Experiments have been carried out on copper powder electrodeposition by constant overpotential and constant current on aluminium, graphite, platinum and copper electrodes. It is shown that for one and the same quantity of electricity, electrode material, electrode surface area, electrolyte, temperature and time of deposition, different particle size distribution curves, current efficiency and specific energy consumption are obtained in galvanostatic and potentiostatic deposition.     

Electrochemical treatment of waters with BDD anodes: kinetics of the reactions involving chlorides

In this work the products of the oxidation at BDD anode of chloride ions in aqueous solutions were identified during galvanostatic electrolyses performed in a filter-press reactor operating both in batch and continuous mode. A set of experiments were preformed in order to study the effect of operating conditions (current density, residence time, hydrodynamics and chloride concentration) on distribution and concentration of electrolysis by-products. As a comparison experiments were also performed using a commercial DSA anode. A simple mathematical model was formulated, and the model predictions agree with the experimental data in a wide range of experimental conditions. The results of this work showed that at low chloride concentrations electrolysis with BDD anode produce a mixture of powerful oxidant: low current density, high mass transfer conditions and low residence time were found as optimal conditions to maximize the concentration of oxidants and minimize the concentration of chlorates. The proposed reaction mechanism may also justify the controversial effect of chloride ions in wastewater treatments: the electrolysis carried out with BDD anodes and electrolyte containing chloride concentration higher 1 g/L could meet the target of the process only if the active chlorine is effective in oxidation of the pollutant that must be removed.     

A method for determining anode and cathode impedances of a direct methanol fuel cell running on a load

A new method for measuring separately anode and cathode impedances (Z_A and Z_C) of an electrochemical generator running on constant load is proposed. In these conditions, the measurement of Z_A and Z_C is not as simple as under galvanostatic conditions. Measurements are carried out first on a dummy cell and next on a commercial direct methanol fuel cell (DMFC) under galvanostatic conditions and using the new proposed method. The comparison of the results validate our method, showing that it is a powerful method for fuel cell electrochemical impedance spectroscopy (EIS) characterization under natural running conditions.     

Zinc–cobalt alloy electrodeposition from chloride baths

Electrodeposition of Zn–Co alloys on iron substrate from chloride baths under galvanostatic and potentiostatic conditions were carried out. Current density, temperature and cobalt percentage in the bath were found to strongly influence the composition of the deposits and their morphology. Changes in potentials, current efficiency and partial current densities were studied. The results show that the shift in potential and in the cobalt percentage of the deposits, for a particular current density during galvanostatic electrodeposition, does not always correspond to the transition from normal to anomalous codeposition. This shift is attributed to zinc ion discharge, which passes from underpotential to thermodynamic conditions. In the range of potentials for the underpotential deposition of zinc, the electrodeposition of zinc–cobalt alloys is discussed, emphasizing the influence of the electrode potential on the composition and microstructure of the deposits.     

A study of the kinetics of passive layer formation on CrMo alloys

Electrochemical measurements on alloys of the two pure metals chromium and molybdenum in the concentration range up to 20 wt% Mo were carried out. The investigations took place under stationary and non-stationary conditions.Stationary current-potential curves show that the behaviour in the active region is mainly determined by molybdenum. The active state, easily obtained for pure chromium, first appears in 5N HCl solution for the 10 wt% alloy; for the 20 wt% alloy it does not appear at all. This corresponds to the behaviour of pure molybdenum, for which an active region in aqueous electrolytes could not clearly be found.In contrast to this no specific influence of molybdenum could be found in the passive and transpassive region. The behaviour of the alloys is quite similar to that of pure chromium. This is indicated by galvanostatic switch-on and potentiostatic step experiments. As for pure chromium the results may be interpreted in terms of the simultaneous-place-exchange mechanism.     

Underpotential deposition of Tl on Ag in the presence of bromide ions – Estimation of specific capacitance for design of electrochemical supercapacitors

The analysis of underpotential deposition (UPD)-based systems for the development of electrochemical supercapacitors is investigated employing the UPD of Tl on Ag in the presence of bromide ions, as an illustrative example. The specific capacitance is estimated with the help of multi-cycle voltammograms, galvanostatic charge/discharge experiments and impedance spectroscopy. The equivalent circuit for the system is constructed and the parameters are deduced from the simulation. The deduced magnitude of ∼10² F g⁻¹ in conjunction with the satisfactory number of charge/discharge cycles obtained from galvanostatic experiments indicate the feasibility of these systems as supercapacitors.     

Electro-recovery of gold and silver from a cyanide leaching solution using a three-dimensional reactor

The selective electro-recovery of gold and silver values from cyanide leaching solutions containing copper was accomplished in a three-dimensional (3D) electrochemical reactor. This case let to contrast three different points of view when dealing with a composed metallic solution: First, the thermodynamic predictions; second, the microelectrolysis approach and finally, the macroelectrolysis experiments. Standard electrode potentials for the study solution would indicate a tendency for gold to deposit first. However, microelectrolysis studies of the three-metallic solution indicated that gold and silver are co-deposited onto a Vitreous carbon (VC) electrode without copper interference in a narrow potential range. Mass balances during the macroelectrolysis experiments (batch model assuming mass transfer control) indicated a preferential deposition of silver during the first ten minutes, even if gold deposition also occurred. On the other hand, values of Stanton (St) for different linear flow velocity corroborated that metals concentration gradients may establish a limit to make profitable the fluid velocity increase in an electrochemical flow cell. Electrolysis experiments were carried out under potentiostatic (at −1400 mV versus SCE) and galvanostatic (at −3.9 Am⁻²) conditions in the FM-01 LC flow cell.     

Electrochemical Removal of Copper Ions from Aqueous Solutions Using a Modulated Current Method

The use of porous electrodes to remove toxic metals from industrial effluents has been recognized over the years due to its high mass transfer rates resulting in high current efficiencies (CE) and low energy consumption (EC), even at very low metal concentrations. This work addresses the effects of flow velocity and electric current on current efficiency and energy consumption of copper electrodeposition using reticulated vitreous carbon, aiming to optimize the CE and EC by using a modulated current method. First, it was found that a flow velocity of 0.246 m s^?1 maximizes the mass transfer coefficient (k_m). Applying this flow velocity and a modulated current, the electrodeposition process was investigated and compared with that carried out under galvanostatic mode. The results showed that using a current control there is a reduction of average EC due to the improvement of the average CE, but the operational time also increases when compared to that obtained using the galvanostatic mode.     

Electrocatalytic oxygen reduction with thiospinels and other sulphides of transition metals

Thiospinels and other sulphides were examined systematically with regard to their electrocatalytic activity for oxygen reduction in acid electrolyte. The measurements were carried out by potentiodynamic and galvanostatic methods. The metals cobalt, iron and nickel show the highest activity in sulphur compounds, the best results being obtained by cobalt. Other transition metals reduce the activity. A considerable decrease in activity is observed when sulphur is partly or totally replaced by oxygen, selenium or tellurium; the same effect is observed with disulphides. A simple interpretation of the results obtained is possible considering the geometric and electrostatic conditions in the spinels.     

纳米聚苯胺的微乳液法制备及电容性能研究

用微乳液法制备了纳米聚苯胺,并将其与活性炭混合制备聚苯胺／活性炭电极。用透射电镜对聚苯胺的形貌进行了表征,用循环伏安法及恒流充放电法对所制电极的电化学性能进行了研究。结果表明：纳米球形聚苯胺的粒径在30～40nm之间,所制得的电极比容为610．3F·g-1（0．5mol／LH2SO4）,显著高于纯活性炭电极的比容171．2F·g-1;在5mA·cm-2的充放电电流密度下,充放电1000次后比容为首次放电比容的71．3％;这表明纳米聚苯胺的加入能显著提高电极的电化学性能。用此组装的非对称型超级电容器的性能也优于用纯活性炭组装的对称型超级电容器,表明纳米聚苯胺是一种性能优异的超级电容器电极材料。     

A study of PtRuO2 catalysts thermally formed on titanium mesh for methanol oxidation

Platinum-based catalysts, for the electro-oxidation of methanol, have been made by thermal decomposition of chloride precursors onto titanium mesh. The catalysed electrodes were successfully operated in acidic methanol electrolytes. Electrochemical characterisation has been carried out using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarisations. A complete analysis of the electrochemical results showed that the preliminary performance of the catalysed titanium mesh was comparable to that achieved with carbon-supported PtRu catalysts. The catalysts formed on titanium mesh by thermal decomposition also exhibited dimensional stability. Catalysed titanium mesh therefore appears to be a promising alternative to carbon-supported catalysts for certain fuel cell applications.     

Activation of Elemental Sulfur by Electrogenerated Cyanomethyl Anion: Synthesis of Substituted 2‐Aminothiophenes by the Gewald Reaction

The activation of elemental sulfur (S₈) has been achieved by means of electrogenerated cyanomethyl anion [easily obtained by galvanostatic reduction from acetonitrile/tetraethylammonium hexafluorophosphate (MeCN‐Et₄NPF₆)]. The “activated” sulfur reacted with ylidenemalononitriles to give substituted 2‐aminothiophenes in very high yields. This variation of the Gewald reaction has been carried out using only catalytic amounts of electricity and supporting electrolyte. A proposed mechanism for the interaction between S₈ and cyanomethyl anion is described.     

Cu-based amorphous alloy electrodes for fuel cells

The present work describes the characteristics of Cu–Zr and Cu–Ti amorphous alloys as catalysts for oxidation of methanol and formaldehyde in alkaline solutions. Two Cu-based amorphous alloys, Cu₆₀Zr₄₀ and Cu₆₀Ti₄₀ both prepared by melt spinning were investigated. Two types of electrode were used: as-quenched amorphous alloys and surface-activated amorphous alloys. The surface-activation treatment consisted in the immersion of the ribbons in 1 M HF solution for 30 s. The determination of the oxidation activity of methanol and formaldehyde was carried out by galvanostatic and by steady-state polarization measurements and cyclic voltammetry experiments in 1 M NaOH solutions containing CH₃OH or CH₂O, deoxygenated by nitrogen bubbling for 30 min at 30 °C. The HF-treated amorphous alloys exhibit catalytic activity only for formaldehyde oxidation; Zr-based alloys show higher current densities than pure crystalline copper and Ti-based alloys.     

Electrochemical homolytic and heterolytic coupling of activated olefins in the absence and presence of benzyl bromide in microemulsion

Electrochemical reduction of four activated olefins namely cyclohexenone (CH), cyclopentenone (CP), methylmethacrylate (MMA), acrylonitrile (AN) in the absence and presence of benzylbromide (BBr) were investigated in CTAB/n-hexane/n-butanol/water based bicontinuous microemulsion (μE). Both cyclic voltammetric studies and galvanostatic preparative electrolysis were carried out. Cyclic voltammetric results in μE were also compared with those in N,N-dimehtylformamide (DMF) medium. Adsorption effects are observed both in DMF and μE. AN undergoes one electron reduction in aprotic solvent and two electron reduction in μE. CH, CP, BBr undergo one electron reduction and yield significant homolytic coupled products under galvanostatic conditions. AN and MMA lead to two electron reduction under identical conditions. In the presence of BBr, CH and CP alone yield significant heterolytic coupled products with simultaneous competitive resin formation. Reduction of AN leads to the formation of a identifiable quantity of propylamine and 3-phenylpropylamine in the absence and in the presence of BBr, respectively.     

Structure and electrochemical capacitance of carbon cryogels derived from phenol-formaldehyde resins

Highly porous carbon cryogels derived from phenol-formaldehyde (PF) resin formulated in ethanol have been prepared and investigated. Different P/F molar ratios have been used for obtaining a series of alcogels that have been freeze-dried and next pyrolysed at 900 °C. Carbonaceous materials having different bulk densities and textural properties have thus been obtained. These materials were fully characterised by helium and mercury pycnometry, mercury porosimetry, nitrogen adsorption, and tested as porous electrodes of electrochemical double-layer capacitors working in 4 M H₂SO₄ aqueous electrolyte. For that purpose, cyclic voltammetry and galvanostatic charge/discharge experiments have been carried out. The derived specific capacitances, around 100 F/g, were shown to depend strongly both on pore availability to the electrolyte and on average micropore width. The cryogel having the highest surface area and micropore volume is thus the one presenting the lowest capacitance because of its poorly accessible and too narrow microporosity.     

Electrolytic synthesis of succinic acid in a flow reactor with solid polymer electrolyte membrane

This paper describes the galvanostatic synthesis of succinic acid from maleic acid in an ion exchange membrane flow cell. The electrolysis was carried out at stainless steel, lead and copper cathodes under variable conditions of current density and substrate concentration. Depending upon the experimental conditions, the yield of succinic acid varied from 95 and 99% with a coulombic efficiency of 80–99%. The product was characterized by various physicochemical techniques, viz. ¹H-NMR, IR and UV–Visible spectroscopy and elemental analysis. The operational conditions giving maximum yield of product were identified. The mechanism of electrochemical reduction of maleic acid and advantages of using a catholyte without supporting electrolyte are discussed.     

旋风分离器结构优化试验

旋风分离器在石油化工和天然气集输领域应用十分广泛,利用化工方面的经验,通过大量的性能对比实验来对旋风分离分离效率进行优化,首先对分离单管按原设计尺寸进行对次重复对比标定实验,然后以此为基础进行改进单管的研制实验,针对加灰斗和4种不同的灰斗开缝结构展开试验,优选出一种在分离效率、压降两方面都具有优势的最佳结构,试验表明KD结构最优。