Effect of Mg2+, Li+, Na+ and K+ on the Electrocrystallization of Nickel from Aqueous Sulfate solutions containing Boric Acid

The effects of metal ions such as Mg²⁺, Li⁺, Na⁺ and K⁺ on the cathodic current efficiency, deposit morphology, crystallographic orientation and polarization behaviour during nickel deposition on stainless steel from aqueous sulfate solutions containing boric acid were investigated. There was virtually no change in current efficiency in presence of these metal ions, but changes were observed in the deposit morphologies and crystal orientations even though all the deposits looked bright, smooth and coherent. Changes were also observed in the polarization behaviour during nickel electrocrystallization in presence and absence of boric acid. An attempt has been made to correlate the effect of these metal ions on various parameters studied.     

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.     

Effects of 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO<Subscript>4</Subscript> on zinc electrodeposition from acidic sulfate electrolyte

A comparative study of the effect of 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ and gelatine on current efficiency (CE), power consumption (PC), deposit morphology, and polarization behaviour of the cathode during electrodeposition of zinc from acidic sulphate solutions were investigated. Compared with the traditional industrial additive, gelatine, the addition of [BMIM]HSO₄ was found to increase current efficiency, reduce power consumption, and improve the surface morphology. Maximum CE and minimum PC were obtained at the addition dosage of 5 mg dm⁻³. Meanwhile, simultaneous addition of the two additives induced a blocking effect of the zinc reduction and led to more leveled and fine-grained cathodic deposits. Moreover, cyclic voltammetry results and kinetic parameters such as Tafel slope, transfer coefficient, and exchange current density obtained from Tafel plots led to the conclusion that both additives have a pronounced inhibiting effect on Zn²⁺ electroreduction. The data obtained from X-ray diffractogram revealed that the presence of additives did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

Effects of temperature and current density on zinc electrodeposition from acidic sulfate electrolyte with [BMIM]HSO<Subscript>4</Subscript> as additive

The effects of temperature and current density on cathodic current efficiency, specific energy consumption, and zinc deposit morphology during zinc electrodeposition from sulfate electrolyte in the presence of 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO₄) as additive were investigated. The highest current efficiency (93.7%) and lowest specific energy consumption (2,486 kWh t⁻¹) were achieved at 400 A m⁻² and 313 K with addition of 5 mg dm⁻³ [BMIM]HSO₄. In addition, the temperature dependence of some kinetic parameters for the zinc electrodeposition reaction was experimentally determined. Potentiodynamic polarization sweeps were carried out to obtain the expression for each parameter as a function of temperature. In the condition studied, the exchange current density depended on temperature as ln(i ₀) = −a/T + b and the charge transfer coefficient was constant. Moreover, the adsorption of the additive on cathodic surface obeyed the Langmuir adsorption isotherm. The associated thermodynamic parameters indicated the adsorption to be chemical.     

Effect of nickel in zinc electrowinning under periodical reverse current

The effects of nickel impurities were investigated during the electrowinning of zinc in acidic media using periodical reverse current (PRC) along with anodic potential current response and cathodic current efficiency. The chemical and structural characteristics of the cathode deposit were also determined using nickel concentrations of 3, 5 and 10 mg l^–1 in sulphuric acid (200 gl^–1 H₂SO₄) containing 60 gl^–1 of zinc. The cathodic current efficiency drop caused by nickel was less detrimental in PRC than DC. It was found that the morphology of the deposit plays an important role in the redissolution process caused by impurities. The levelling effect caused by PRC decreases the rate of zinc redissolution, which results in an increase of current efficiency. However for concentrations equal to or greater than 10 mgl^–1, the levelling effect caused by PRC is no longer dominant. On the anode nickel did not affect the overpotential of the lead-silver electrode in PRC or DC modes.     

Effects of antimony(III) on zinc electrodeposition from acidic sulfate electrolyte containing [BMIM]HSO<Subscript>4</Subscript>

The effect of antimony(III) on the cathodic current efficiency (CE), power consumption (PC), deposit morphology, and polarization behavior during electrodeposition of zinc from acidic sulfate solutions containing 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ was investigated. The results indicated that the addition of Sb(III) alone decreased the CE, increased the PC, and deteriorated the quality of the zinc electrodeposits. However, the combined addition of Sb(III) and [BMIM]HSO₄ was found to be beneficial for zinc deposition and improved the surface morphology of the zinc electrodeposits. Maximum CE and minimum PC were obtained at the combined addition of 0.02 mg dm⁻³ Sb(III) and 5 mg dm⁻³ [BMIM]HSO₄. Depolarization of the cathode was noted in the presence of Sb(III) alone in the electrolyte whereas this effect was partly counteracted by the addition of [BMIM]HSO₄. Cathodic polarization curves were traced and analyzed to determine the electrokinetic parameters such as Tafel slope, transfer coefficient, and exchange current density so as to elucidate the nature of the electrode reactions. The data obtained from X-ray diffractogram revealed that the presence of Sb(III) did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

Effects of [HMIM]HSO<Subscript>4</Subscript> and [OMIM]HSO<Subscript>4</Subscript> on the electrodeposition of zinc from sulfate electrolytes

The effects of the organic additives 1-hexyl-3-methylimidazolium hydrogen sulfate ([HMIM]HSO₄) and 1-octyl-3-methylimidazolium hydrogen sulfate ([OMIM]HSO₄) on current efficiency (CE), power consumption (PC), polarization behavior of the cathode, deposit morphology, and crystallographic orientation during electrodeposition of zinc from acidic sulfate solution were investigated. The results were compared with those of a common industrial additive, gum arabic. Addition of these additives increases current efficiency, decreases power consumption, and improves the surface morphology at lower concentrations. Both the additives showed similar polarization behavior to gum arabic and the extent of polarization was in the order: gum arabic > [OMIM]HSO₄ > [HMIM]HSO₄. The nature of the electrode reactions was studied through measurements of Tafel slopes, transfer coefficients, and exchange current densities. Data obtained from X-ray diffractogram revealed that the presence of any of these additives did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

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.     

Preparation and properties of raney nickel electrodes on Ni-Zn base for H2 and O2 evolution from alkaline solutions Part I: electrodeposition of Ni-Zn alloys from chloride solutions

Experimental results for the electrodeposition of Ni-Zn alloys from chloride solutions, with addition of H₃BO₃ and without other additives, in a laboratory cell with a perforated nickel sheet cathode and with recirculating electrolyte are presented. The dependence of the zinc content in the alloy on the following operating conditions was investigated: cathodic current density, 1.0–20.0 A dm^–2; temperature, 35–65°C; pH 1.5–5.5; total molarity,M _tot=M _Ni ²⁺ +M _Zn ²⁺ =1.1–2.8 M; and, molar ratio,P=M _Ni ²⁺ /M _Zn ²⁺ =1.0–15. Depending on the operating conditions the Zn content in the alloy varied over the range 22–88 mol%. In separate experiments galvanostatic polarization curves were measured in the direction of increasing and then decreasing cathodic current density in the range 0.1–20.0 A dm^–2 with all other operating conditions as used for electroplating experiments. In all cases significant hysteresis effects were observed. It was found that the current efficiency for the electrodeposition of Ni-Zn alloys from chloride solutions as a function of the zinc content in the alloy showed a sharp minimum of about 55% atX _Zn=55 mol % irrespective of other operating conditions.     

Role of Mo<Superscript>6+</Superscript> during nickel electrodeposition from sulfate solutions

The effect of Mo⁶⁺ on the current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from sulfate solutions was investigated. Mo⁶⁺ did not have a significant effect on current efficiency over the concentration range 2–100 mg dm⁻³. However; a decrease in current efficiency by a magnitude of more than 20% was seen at 500 mg dm⁻³. The quality of the nickel deposit with reference to the visual appearance and contamination level varied with varying concentration of Mo⁶⁺; this was also reflected in the morphology and crystallographic orientations of the deposits. Addition of Mo⁶⁺ to the electrolyte introduced two new crystal planes i.e., (220) and (311). Depolarisation of the cathode was noted at lower concentrations of Mo⁶⁺ (2–40 mg dm⁻³) whereas polarisation of the cathode was observed at Mo⁶⁺ concentration >40 mg dm⁻³ .The effect of Mo⁶⁺ on parameters such as Tafel slope (b), transfer coefficient (α) and exchange current density (i ₀) were also determined.     

The effect of Co2+, Cu2+, Fe2+ and Fe3+ during electrowinning of nickel

The effects of the impurities Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺ on the current efficiency, physical appearance, purity, crystallographic orientation and surface morphology of the deposit and on nickel deposition polarization behaviour during nickel electrowinning were determined. The current efficiency did not change significantly in the presence of these impurities over the concentration range studied, but certain changes in the purity and physical appearance of the deposit were observed. Based on the physical appearance of the electrodeposited nickel, the tolerance limits of the impurities in the electrolyte are reported. The tolerance limit of Co²⁺ was a maximum at 500 p.p.m. and a minimum at 5 p.p.m. in the case of Fe²⁺. No deviation of nickel structure from fcc was observed in the presence of any of these impurities but the peak height values for different orientations showed variations with all the impurities and the values also changed with increase in the impurity concentrations. The surface morphology of electrodeposited nickel also changed in the presence of the impurities. The potentiodynamic scan curves for electrodeposition of nickel showed deviations in the presence of all the impurities except Cu²⁺. Based on the results, an attempt is made to correlate the effects of the various factors investigated.     

超声波对硫酸盐镀镍及镀层性能的影响研究

研究了硫酸盐镀镍过程中施加超声波对阴极极化能力、阴极电流效率、分散能力、电化学反应阻抗、镀层内应力和硬度的影响。结果表明,镀镍过程中施加超声波能够降低阴极极化、提高阴极电流效率、改善电解液的分散能力、减小镍沉积阻抗;还能细化镀层晶粒、降低镀层内应力、提高镀层的硬度。     

Pulse current electrodeposition of Al from an AlCl3-EMIC ionic liquid

Electrodeposition of aluminum from an AlCl₃-EMIC ionic liquid with or without the addition of saturated LaCl₃ was carried out by both direct- and pulse-current plating methods. The effects of various parameters, including current density, pulse frequency, current on/off duration (t_on and t_off), and temperature, on deposit morphology and crystal size were investigated. Deposits prepared by pulse-current plating gave a brighter and flatter surface than those prepared by direct-current plating at appropriate pulse current parameters. Temperature and pulse–current frequency (t_off) were shown to significantly affect deposit morphology. Coalescence of grains during t_off periods in the pulse current plating was observed, especially at temperatures above 60 °C. Increasing the temperature from 25 to 90 °C caused an increase in deposit grain size and resulted in a change of grain shapes from a small sphere-like form to a feather-like form. As a result, the adhesion of the deposited aluminum to the substrate was lowered. Smaller grain sizes and well-adhered deposits were achieved at lower temperatures. For example, deposition at 25 °C resulted in the smallest crystal size of about 0.3 μm under the conditions of t_on = 80 ms, t_off = 20 ms, and i = 8 mA/cm². Furthermore, the addition of LaCl₃ to the melt at 60 °C effectively reduced the porosity and improved compactness of deposits.     

Anomalous codeposition of Co–Ni: alloys from gluconate baths

Thin films of cobalt–nickel alloys were galvanostatically deposited onto steel substrates from gluconate baths. Cathodic polarization curves were determined for the parent metals and Co–Ni alloy. The effects of bath composition, current density and temperature on cathodic current efficiency (CCE) and alloy composition were studied. The deposition of Co–Ni alloy is of anomalous type, in which the less noble metal (Co) is preferentially deposited. The CCE of codeposition is high and increases with increase in temperature and current density, but it decreases as the [Co²⁺]/[Ni²⁺] ratio in the bath increases. The percentage of Co in the deposit increases with increasing cathodic current density, temperature and increasing Co²⁺ ion concentration. The structure and surface morphology of the deposit were studied by XRD, ALSV and SEM. The results showed that the alloys consisted of a single solid solution phase with a hexagonal close packed structure.     

High-rate electrochemical dissolution of Ni–Cu alloys in nitrate electrolyte

High-rate anodic dissolution of nickel, copper, and two alloys Ni30Cu70 and Ni65Cu32 in NaNO₃ solution was studied, using a flow-channel electrochemical cell. In all experiments, the initial interelectrode distance was 208 m and the electrolyte velocity was 15 m s^–1. The dependence of the current efficiency and surface brightening on the current density was determined. Voltage transients at various current densities were measured and voltammograms were constructed. Compared to nickel and copper, the alloys showed intermediate behaviour, especially at j > j ₁. The shape of the voltage transients and the occurrence of surface brightening were more suitable to detect the existence of a limiting current region than voltammograms, especially for Ni. Using the voltammograms and literature data, anodic and cathodic potentials and the voltage drop in the interelectrode gap at a given current density were estimated for j < j ₁.     

Effect of chromate ion on zinc electrowinning from acid sulphate electrolyte

The effect of chromate ion and its interaction with antimony and glue on zinc electrowinning from acid sulphate electrolyte were studied. During electrolysis at 430 A m^–2 and 45°C, the chromate ion was found to polarize the cathodic reaction resulting in a refined zinc deposit having a morphology featuring a vertical orientation of the zinc platelets. Although chromium did not codeposit, the current efficiency for zinc deposition was dramatically decreased in the presence of > 1000 mg dm^–3. This effect became more pronounced when the electrolyte also contained additives such as antimony and glue.     

Electrodeposition of Co–Cu alloy coatings from glycinate baths

The cathodic polarization, cathodic current efficiency of codeposition, composition and structure of Co–Cu alloy as a function of bath composition, current density and temperature were studied. Electrodeposition was carried out from solutions containing CuSO₄ · 5H₂O, CoSO₄ · 7H₂O, Na₂SO₄ and NH₂CH₂COOH. The cathodic current efficiency of codeposition (CCE) was high and it increased with increasing temperature and Cu²⁺ content in the bath, but it decreased with current density. The codeposition of Co–Cu alloys from these baths can be classified as regular. The Co content of the deposit increased with Co²⁺ content and current density and decreased with glycine concentration and temperature. The structure of the deposited alloys was characterized by anodic stripping and X-ray diffraction techniques. The data showed that the deposited alloys consisted of a single solid solution phase with a face-centred cubic (f.c.c.) structure.     

1,4-丁炔二醇对硫酸盐镀镍液及镀层性能的影响

研究了硫酸盐镀镍电解液中1,4-丁炔二醇对电解液电流效率、分散能力、阴极极化及镍镀层光亮度、硬度及内应力的影响.采用扫描电镜和X-射线衍射分析表征了镍镀层表面形貌和微观结构.结果表明,1,4-丁炔二醇的加入使镍镀层的光亮度有所改善,但达不到镜面光亮;而对电解液的电流效率、分散能力影响不大;当ρ(1,4-丁炔二醇)达0....     

Electroplating of cadmium from acidic bromide baths

Earlier work on the electroplating of cadmium from acidic bromide solution containing 0.3M CdBr₂·4H₂O, 0.1M HC1, 0.4M H₃BO₃ and 2.0M KBr (Bath I) has been reviewed and extended to an examination of the influence of the organic additives 5g gelatin 1^–1 and 2.5g melamine 1^–1 (Bath II). The effects of the plating current density, plating time and pH on the cathodic polarization and the current efficiency of cadmium electroplating from Bath II, as well as on the morphology and the microhardness of the as-plated cadmium electrodeposits are discussed. It was observed that the additivecontaining Bath II yields more coherent, brighter and harder cadmium plates than the additive-free Bath I. The optimum operating conditions for obtaining satisfactory plates from Bath II at 25° C are:i=0.6–1.6 A dm^–2;t=10–15 min and pH 3.6–1.9.     

Cathodic protection of carbon steel in natural seawater: Effect of sunlight radiation

Cathodic protection of metals in seawater is known to be influenced by chemical–physical parameters affecting cathodic processes (oxygen discharge, hydrogen evolution and calcareous deposit precipitation). In shallow seawater, these parameters are influenced by sunlight photoperiod and photosynthetic activity. The results presented here represent the first step in studies dedicated to cathodic protection in shallow photic seawater. This paper reports on carbon steel protected at −850 mV vs. Ag/AgCl (oxygen limiting current regime) in the presence of sunlight radiation but in the absence of biological and photosynthetic activity, the role of which deserves future research. Comparison of results obtained by exposing electrochemical cells to daylight cycles in both biologically inactivated natural seawater and in NaCl 3.5 wt.% solutions showed that sunlight affects current densities and that calcareous deposit interfere with light-currents effects. Sunlight radiation and induced heating of the solution have been separated, highlighting results not otherwise obvious: (1) observed current waves concomitant with sunlight radiation depend fundamentally on solar radiation, (2) solar radiation can determine current enhancements from early to late phases of aragonite crystal growth, (3) a three-day-old CaCO₃ layer reduces but does not eliminate the amplitude of the current waves. Theoretical calculations for oxygen limiting currents and additional field tests showed that sunlight, rather than bulk solution heating, is the main cause of daily current enhancements. This was confirmed by polarizations performed at −850 and −1000 mV vs. Ag/AgCl (constant bulk temperature), during which the electrode was irradiated with artificial lighting. This test also confirmed O₂ discharge to be the cathodic process involved. A mechanism of radiation conversion to heat in the oxygen diffusion layer region is proposed.