Barrel zinc electrodeposition from alkaline solution

This paper discusses the influence of electrochemical parameters on the concentration–time relationship in an electrolytic zinc deposition reactor using a three-dimensional electrode. The dynamic behaviour of a zinc plating unit is obtained from the fundamental material balance. Two stages are considered: (i) the batch electrolytic reactor, and (ii) the electrolyser surrounded by rinses (i.e., contribution of drag-out). This theoretical approach shows that good control of the operating parameters helps stabilise the zinc electrolyte and, therefore, the properties of the zinc deposits. The aim of the experiments is to investigate, in a statistically designed test program, the effects of the composition of the alkaline zinc electrolyte on cathode efficiency and on the morphologies/textures of the deposits.     

Effect of brighteners on hydrogen evolution during zinc electroplating from zincate electrolytes

Hydrogen evolution during zinc electrodeposition on a steel substrate from zincate electrolytes containing different additives was studied using various experimental techniques.The hydrogen evolution reaction is limited by the electron transfer step. Hydrogen evolution is most intensive during the first seconds from the beginning of electrodeposition due to the lower overpotential of hydrogen on steel as compared with that on zinc. The evolved hydrogen is dissipated in three ways. Most is dissipated to the atmosphere via gas bubbles at a constant rate. Some is dispersed in the electrolyte some diffuses into the steel substrate, predominantly at the commencement of deposition. The additives affect both the total amount of evolved hydrogen and its distribution. The highest amount of hydrogen is evolved in the presence of the anisaldehyde bisulphite containing composite additive. The highest amount of hydrogen included in the substrate and remaining in the electrolyte corresponds to the use of the Na–N-benzylnicotinate containing additive. In this case blistering is observed.     

Li-LiFePO4 rechargeable polymer battery using dual composite polymer electrolytes

A composite polymer electrolyte, formed by dispersing into a poly(ethylene oxide)-lithium salt matrix two additives, i.e. calyx(6)pyrrole, (CP) acting as an anion trapper and superacid zirconia, S-ZrO₂ acting as a conductivity promoter, has been tested as a separator in a new type of rechargeable lithium battery using lithium iron phosphate as the cathode. The choice of the electrolyte was motivated by its favourable transport properties both in terms of lithium ion transference number and of total ionic conductivity. The choice of the cathode was motivated by the value of its operating voltage which falls within the stability window of the electrolyte. The performance of the battery was determined by cycling tests carried out at various rates and at various temperatures. The results demonstrate the good rate capability of the battery which can operate at high charge-discharge efficiency even at 1 C rate and that it can be cycled at 90 °C with a satisfactory initial capacity of the order of 90 mAh g⁻¹. These values outline the practical relevance of the composite electrolyte membrane and of its use as separator in a lithium battery. H. H. Sumathipala—On leave from Department of Physics University of Kelaniya, Kelaniya, Sri Lanka.     

锌电解液中杂质离子的行为研究进展

在电沉积锌过程中,锌电解液中的杂质离子对电流效率、电能损耗和沉积锌的质量有很大影响.本文分别介绍了铜、钻、镍、铁、镉、铅和砷、锑、锗等杂质离子对锌电沉积过程的影响机理,综述了锌电沉积过程中杂质离子对电流效率、锌沉积层的质量和形貌等的影响的研究状况,为获得高质量的锌沉积层提供参考.     

A Modified Hull Cell and its Application to the Electrodeposition of Zinc

An analytical electrochemical cell based on the Hull cell is described. The cell was tailored specifically for the analysis of electrowinning or electroplating. Current density distributions were generated by asymmetric insertion of an insulating baffle between parallel electrodes. The position and length of the baffle were easily altered, giving 12 possible distributions for a single total current. The cathode consisted of 10 electrically isolated 1cm², aluminium segments. By logging the potential drop across 1 resistors in each of the 10 isolated parallel branches, quantitative determination of current densities across the cathode was made possible. The small segments facilitated microscopic analysis of deposit morphologies. A technique for the determination of current efficiencies on each segment is described and demonstrated. The technique obviates the necessity to determine deposited masses directly. Development of the technique for industrial application is detailed. The system is demonstrated by evaluating known effects of variables in zinc electrowinning. The variables examined were temperature, deposition time, acid concentration and antimony contamination.     

Hydrogen evolving activity on nickel–molybdenum deposits using experimental strategies

Hydrogen evolution on various Ni–Mo deposits was systematically compared using fractional factorial design (FFD) and response surface methodology (RSM). The electroplating variables such as pH, Ni/Mo atomic ratio and citrate concentration were found to be the key factors affecting the hydrogen evolution activity from the FFD study. The effects of Ni/Mo atomic ratio and citrate concentration in the plating bath on the apparent current density, the exchange current density, and the specific activity (based on i/q ^*) of hydrogen gas evolution, and on the Mo/(Ni + Mo) ratio of the deposits were examined using regression models. These models, represented as response surface contour plots, showed the maximum hydrogen evolving activity occurring on the Ni–Mo deposit electroplated from the bath with a pH of 8, a Ni/Mo ratio of 3.3 and a citrate concentration of 40 g l^–1, respectively.     

Effect of pyridine and its derivatives on the electrodeposition of nickel from aqueous sulfate solutions. Part II: Polarization behaviour

The electrochemical reactions occurring during electrodeposition of nickel from acidic sulfate solutions were examined by cyclic and linear sweep voltammetry techniques. The effect of pyridine, 2-picoline and 4-picoline on the electrode polarization behaviour and electron transfer parameter of the cathodic reduction process was also investigated. Strongest electrode polarization was seen with 4-picoline. The order of cathodic polarization was 4-picoline > 2-picoline > pyridine. Kinetic parameters such as Tafel slope, transfer coefficient and exchange current density were determined to analyse the nature of the electrode reactions. The exchange current density for nickel deposition on nickel and stainless steel substrates was in the order 4-picoline < 2-picoline < pyridine.     

Role of additives in bright zinc deposition from cyanide free alkaline baths

A new additive formulation for non-cyanide alkaline zinc baths was identified after experiments with various additives. Polyvinyl alcohol addition was found to be the best primary additive of those tested. The secondary additives selected belonged to the aldehyde group. The selection of the additives was made based on Hull cell, cathode current efficiency and throwing power studies. Thickness measurements at various points on a cathode indicated uniform thickness distribution. XRF showed uniform deposition. SEM examination indicated a fine-grained deposit structure. Finally, the influence of each additive was studied using cyclic voltammetry.     

Composition control of tin-zinc deposits using experimental strategies

The robust electroplating settings of a direct-current (dc) plating mode for the co-deposition of Sn-Zn deposits with their composition close to the eutectic point (i.e., Sn-9Zn) from the chloride solutions were achieved and investigated by using experimental strategies, including the fractional factorial design (FFD) and central composite design (CCD) coupled with the response surface methodology (RSM). The temperature of the plating bath, pH, and the metallic ion ratio (i.e., Sn⁴⁺/Zn²⁺ ratio) were found to be the key factors affecting the composition of Sn-Zn deposits in the FFD study. The effects of pH and temperature of the plating solution on the composition of Sn-Zn deposits were examined using a regression model in the CCD study. This model, represented as contour plots, showed that pH 5.0 and temperature = 78 °C were the robust electroplating settings for the co-deposition of the eutectic Sn-Zn alloys, which was independent of the substrates. In addition, based on the robust plating settings, the composition of Sn-Zn alloys could be precisely controlled and predicted by adjusting the composition of the plating baths. From the morphologies and crystalline information, the binary Sn-Zn deposits prepared in this work should belong to heterogeneous alloys.     

Effect of Pyridine and its Derivatives on the Electrodeposition of Nickel from Aqueous Sulfate solutions Part I: Current Efficiency, Surface Morphology and Crystal Orientation

The effects of pyridine and its derivatives on current efficiency, surface morphology and crystallographic orientations of electrodeposited nickel from acidic sulfate solutions were investigated. The results indicated that the presence of pyridine and picolines had no significant effect on current efficiency. The deposits obtained were smoother, more compact and uniform with picolines than with pyridine. A significant change in surface morphology of the electrodeposits was observed and picolines were found to be better additives than pyridine, 4-picoline being the best. X-ray diffraction revealed that the (200) plane was the most preferred plane and was not affected by the presence of any of these additives in the electrolyte.     

Electrodeposition of nickel in the presence of Al<Superscript>3+</Superscript> from sulfate baths

The effect of Al³⁺ on the cathodic current efficiency, deposit morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from acidic sulfate solutions was investigated. Higher concentration of Al³⁺ (>10 mg dm^–3) significantly deteriorated the surface quality of the nickel deposit as well as the current efficiency. X-ray diffraction studies revealed that the (200) plane was the most preferred crystal plane and was not affected by the presence of varying concentration of Al³⁺ in the electrolytic bath. The presence of Al³⁺ caused polarisation of the cathode, which increased with increasing Al³⁺ concentration. The effect of Al³⁺ on the electrokinetic parameters: Tafel slope (b), transfer coefficient () and exchange current density (i₀) were also investigated.     

Molecular Recognition of the Catalytic Zinc(II) Ion in MMP-13: Structure-Based Evolution of an Allosteric Inhibitor to Dual Binding Mode Inhibitors with Improved Lipophilic Ligand Efficiencies

Matrix metalloproteinases (MMPs) are a class of zinc dependent endopeptidases which play a crucial role in a multitude of severe diseases such as cancer and osteoarthritis. We employed MMP-13 as the target enzyme for the structure-based design and synthesis of inhibitors able to recognize the catalytic zinc ion in addition to an allosteric binding site in order to increase the affinity of the ligand. Guided by molecular modeling, we optimized an initial allosteric inhibitor by addition of linker fragments and weak zinc binders for recognition of the catalytic center. Furthermore we improved the lipophilic ligand efficiency (LLE) of the initial inhibitor by adding appropriate zinc binding fragments to lower the clogP values of the inhibitors, while maintaining their potency. All synthesized inhibitors showed elevated affinity compared to the initial hit, also most of the novel inhibitors displayed better LLE. Derivatives with carboxylic acids as the zinc binding fragments turned out to be the most potent inhibitors (compound 3 (ZHAWOC5077): IC₅₀ = 134 nM) whereas acyl sulfonamides showed the best lipophilic ligand efficiencies (compound 18 (ZHAWOC5135): LLE = 2.91).