Cathodic deposition of amorphous silicon from solutions of silicic acid and tetraethyl ortho-silicate in ethylene glycol and formamide containing HF

Amorphous silicon containing carbon, hydrogen and fluorine were electrodeposited from solutions containing ethylene glycol, hydrofluoric acid, and tetraethyl orthosilicate or silicic acid. The deposits were characterized by electrical resistance and ir reflectance measurements. The deposits exhibited point contact electrical resistances from 10⁴ to 10¹⁴ ohm cm^?1 which could be changed by making suitable changes in the composition of the electrolyte or the conditions of electrolysis. The conductivity of the deposits was changed from p- to n-type by doping with phosphorus achieved by adding triethyl phosphate to the electrolyte.     

Cathodic deposition of molybdenum and vanadium mixed oxyhydroxide films from V-substituted polymolybdophosphate

We report a new electrochemical route for fabricating molybdenum and vanadium mixed oxyhydroxide films on Au electrode from Keggin-type vanadium-substituted polymolybdophosphate. The process involves a potentiodynamic reduction of aqueous 9-molybdo(VI)-3-vanadophosphosphate(V) ([PMo₉V₃O₄₀]⁶⁻) in the potential region between 0 and −0.7 V versus Ag/AgCl. The resulting MoV oxyhydroxide film electrode gave a stable redox behavior in Na₂SO₄ electrolyte of pH 3. X-ray photoelectron spectroscopy revealed that this results from oxidation/reduction of Mo⁵⁺/Mo⁶⁺ in the film which accompanies extraction/insertion of protons for charge compensation. The deposited V ions remained in the film upon repetitive potential cycling without affecting their oxidation state. Voltammetric data in the presence of sodium nitrite showed electrocatalytic activity of the MoV oxyhydroxide toward the electroreduction of nitrite.     

Coelectrodeposition of aluminium and cadmium from aqueous sulphate solutions

Coelectrodeposition of aluminium and cadmium from aqueous solutions is shown to be possible under very restricted conditions. The deposits are in a divided form and contain up to 40% aluminium. Lower cadmium ion concentration in the solutions leads to a higher proportion of aluminium in the deposit and there is an optimum concentration for the sulphuric acid in solution. Faradaic yields for metal electrodeposition are, however, low and hydrogen evolution is the predominant reaction.     

复杂件滚镀光亮铜锡工艺的改进

以某羧酸盐的水溶液作为走位剂(即覆盖能力促进剂),可提高形状复杂的小零件滚镀光亮铜锡时的走位能力。改进后的镀液配方及工艺参数为:CuCN10～20g/L,游离NaCN12～24g/L,SnCl20.5～1.0g/L,Na2HPO490～100g/L,明胶0.1～0.2g/L,走位剂25～35mL/L,温度45～55°C,pH10.5～11.5,电压8～9V,电流300～350A/桶,以电解铜板为阳极。     

Electrodeposition of iron in sulphate solutions

The kinetics of iron electrodeposition from acid sulphate solutions onto a platinum electrode was investigated by means of stationary polarisation curves and electrochemical impedance spectroscopy. Together with interfacial pH data previously obtained, the effect of pH was analysed. The formation of at least three adsorbed intermediates at the cathode surface was evidenced in all pH values. The relative rate of their formation and its surface concentration depend on the solution pH as well as on the electrode potential. It is suggested that two of these species catalyses the H⁺ reduction whereas the other one may have a blocking effect on this reaction.     

Electrolytic deposition of lithium from non-aqueous solutions

This paper describes a study of the deposition of lithium from lithium salts (LiNO₃, LiCl, and LiClO₄) in organic solvents (CH₃CN, (CH₃)₂SO, HCONH₂, HCON(CH₃)₂, CH₃CON(CH₃)₂, and THF) using the potential-sweep technique. The current efficiency for lithium deposition was found to depend on both the solvent used and the particular anion in the electrolyte. In CH₃CON(CH₃)₂, (CH₃)₂SO, and HCON(CH₃)₂ solutions, the current efficiency for lithium deposition increased in the order: lithium chloride < lithium perchlorate < lithium nitrate whereas in CH₃CN it increased on addition of chloride. Addition of water to the LiNO₃-DMF solution also increased the current efficiency for lithium deposition. The solution which gave the highest efficiency was LiNO₃ in CH₃CON(CH₃)₂, in which efficiencies higher than 70% were obtained. The lithium metal deposited electrolytically from the LiNO₃-HCON(CH₃)₂ solution consisted of fine grains and had a high degree of crystallinity with very smooth deposit surfaces.     

Cathodic current efficiency in the chlorate process

Sodium chlorate is produced in undivided electrolysis cells. Hydrogen is evolved on the cathodes, usually made of steel, while chloride ions are oxidised to chlorine on the anodes, usually DSA^®s. Parasitic cathodic reactions, lowering the cathodic current efficiency (CE), are the reduction of hypochlorite and chlorate ions. These reactions are suppressed by the addition of Cr(VI) to the electrolyte. In this work the effects that time of the electrolysis, chromate concentration and interruption of the electrolysis process have on CE has been investigated. New steel, as well as steel samples cut from cathodes used in a chlorate plant, were used as cathode material. Laboratory experiments in a divided cell were made to determine the rate of hydrogen production, and thereby indirectly CE, at varying operating conditions. It was found that the chromate concentration is important for the CE in the range 0.5–6 g l^?1 Na₂Cr₂O₇. The CE was higher on new steel than on the used steel, which had a more corroded and inhomogeneous surface. When starting the electrolysis the CE was initially low, at a value depending on the operating conditions, but increased with time of polarisation. The time to reach an approximate steady CE was generally in the order of hours. Electrolysis shut downs in the presence of hypochlorite (≤ 3 g l^?1 NaClO) resulted in corrosion of iron and a low CE when restarting the process. After one such corrosion shut down the new steel showed as low CE as the used steel. When restarting the electrolysis after a shut down without hypochlorite the CE was higher than before the shut down. Current densities of a simulated bipolar plate during a shut down were measured to 50–150 A m^?2, resulting from oxidation of steel and reduction of oxy chlorides on the catalytic DSA^® electrode.     

Cathodic polarization of copper electrode in CuCN–KCN solutions and the current distribution for copper deposition on grooved substrates

The cathodic polarization of a copper electrode in CuCN/KCN solution was interpreted by considering the diffusion and migration of all ionic species, chemical reactions involving cyano-copper(i) complexes, and the quasiequilibrium of charge transfer reaction. Experimental polarization curves were compared with theoretical ones, where the diffusion layer thickness was determined. The present model was applied to the prediction of thickness distribution of copper coating on grooved substrates. Two types of substrates with grooves of different size (width × depth), (a) 5mm × 5mm and (b) 1mm × 1mm, were used. Agreement between theory and experiment was satisfactory for substrate a, but not for substrate b. The effect of convective mass transfer in the groove was discussed.     

The anodizing of aluminium in sulphate solutions

The morphology of films formed in H₂SO₄---Na₂SO₄ mixtures for different times at various constant cds has been studied as a function of electrolyte concentration, pH and temperature, using electron microscopy. At low pH, local preferential film dissolution competes with the film-forming reaction, producing typical porous films whereas, as the pH is raised towards neutrality, pitting by metal dissolution becomes a progressively more important competitive process, probably initiating at the base of flaws in the film. For porous films, it is shown that the pore diameter, cell diameter and barrier-layer thickness are all proportional to the formation voltage, there being evidence that pore initiation and development are largely controlled by field-assisted oxide dissolution, with possible lesser contributions from Joule heating effects. Severe anodizing conditions produce pore widening and merging, as well as general roughening, at and near the outer surface but, although the film appears less regular and compact, there is no evidence of major pore widening throughout its thickness.     

Separation of copper from cobalt in sulphate solutions by using CaCO3

Lime neutralization is widely used to precipitate heavy metals including copper and cobalt from wastewater. Limestone (calcium carbonate: CaCO₃) is too stable to be used directly for this purpose. Grinding of CaCO₃ in the solutions of copper and cobalt sulphate was conducted to raise its reactivity. During the mechanochemical activation, CaCO₃ reacted with copper sulphate but not significantly with cobalt sulphate and this phenomenon allowed an easy separation of copper from cobalt. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of the Co(II) ions remained in aqueous solution.     

无氰滚镀铜锡合金持续增厚工艺

以低碳钢圆饼为基体,在焦磷酸盐溶液体系中滚镀制备厚度为20μm以上的低锡铜锡合金。研究了Sn2P2O7的质量浓度、K4P2O7的质量浓度、添加剂JZ-1的用量、阴极电流密度及镀液温度对铜锡合金镀层组成和性能的影响。结果表明,这些因素对镀层的组成、性能和持续增厚都有一定的影响。低锡铜锡合金镀层可持续增厚的镀液组成与工艺条件为:K4P2O7 350～400g/L,Cu2P2O7·4H2O 20～25g/L,Sn2P2O7 1.5～2.0g/L,K2HPO4·3H2O 60g/L,添加剂JZ-10～0.5mL/L,pH8.5,阴极电流密度0.34～0.46A/dm2,镀液温度25～35℃,滚筒转速15r/min,循环过滤。在上述条件下对钢铁基体滚镀4h可获得平均厚度为20μm以上、锡的质量分数为12%～16%的铜锡合金镀层,该镀层与钢铁基体之间的结合力良好、耐蚀性能好,具有较好的机械性能与物理性能。     

Reversibility of electrochemical magnesium deposition from Grignard solutions

The reversibility of electrochemical magnesium deposition from Grignard reagents was investigated with regard to potential application of magnesium as a negative electrode in rechargeable batteries. The reoxidation rate depends on the morphology of the magnesium deposit which is controlled by the substrate material. Good results were obtained using silver or gold substrates. Magnesium deposits on these materials was found to be of smooth and compact morphology. A nearly complete electrochemical reoxidation and a low self-discharge were observed.     

Effect of thiourea,benzotriazole and 4,5-dithiaoctane-1,8-disulphonic acid on the kinetics of copper deposition from dilute acid sulphate solutions

The effects of thiourea (TU), benzotriazole (BTA) and 4,5-dithiaoctane-1,8-disulphonic acid (DTODSA) on the deposition of copper from dilute acid sulphate solutions have been studied using potential sweep techniques. Tafel slopes and exchange current densities were determined in the presence and absence of these organic additives. TU and BTA were found to inhibit the copper deposition reaction; increases in the BTA concentration gave a systematic lowering of the exchange current density, whilst TU behaved in a less predictable manner. For BTA and TU concentrations of 10^–5 mol dm^–3,j ₀ values of 0.0027 ± 0.0001 and 0.0028 ± 0.0002 mA cm^–2 were obtained compared to a value of 0.0083 ± 0.0003 mA cm^–2 for the additive free acid sulphate solution. In contrast, in the presence of DTODSA, an increased exchange current of 0.043 ± 0.0003 mA cm^–2 was observed. The presence of additives gave rise to measured Tafel slopes of –164, –180 and –190 mV for TU, BTA and DTODSA, respectively, compared to that of –120 mV for copper sulphate alone.List of symbols A electrode area (cm²) - b _C cathodic Tafel slope (mV) - c _B bulk concentration (mol cm^–3) - D Diffusion coefficient (cm² s^–1) - F Faraday constant (A s mol^–1) - I _L Limiting current (A) - j Current density (A cm^–2) - j _CT Charge transfer current density (A cm^–2) - j ₀ Exchange current density (A cm^–2) - k _L Mass transport coefficient (cm s^–1) - R Molar gas constant (J K^–1 mol^–1) - T Temperature (K) - z Number of electrons (dimensionless) Greek symbols _C Cathodic transfer coefficient (dimensionless) - Overpotential (V) - v Kinematic viscosity (cm² s^–1) - Rotation rate (rad s^–1)     

Cadmium removal from aqueous sulphate solutions by treatment with iron felts

The possibility of removing cadmium from effluents byelectrochemical treatment using iron felts as three-dimensional electrodes was investigated. It was found that iron felts remove cadmium by three paths: (i) adsorption of cadmium ions by hydrous ferric oxide, (ii) cathodic electrodeposition and (iii) precipitation of cadmium hydroxide due to the localized alkalinity produced by the hydrogen evolution. The adsorption isotherm, at 30°C, of cadmium ions from an aqueous sulphate solution on hydrous ferric oxide is given. The influence of cathodic potential, volumetric flow rate and interelectrode gap on the current, current efficiency and fractional conversion is discussed. The iron felts proved to be efficient in removing cadmium. The highest fractional conversion, ≌25% for single pass operation, with 100% current efficiency was obtained for a volumetric flow rate of 9·57×10⁻⁶ m³ s⁻¹ using iron felt cathodes of 4×10⁻³ m thickness potentiostated at potentials lower than −1·5 V against a saturated calomel electrode. © 1998 Society of Chemical Industry     

拜耳公司硫酸法钛白的无公害生产

德国拜耳公司作为世界上最大的化工公司之一，十分重视环保，经过３０年的不断开发，其钛白生产完全符合欧共体关于钛白生产的环保指令，作者介绍了硫酸法钛白的无废副生产和开发新产品概况。     

Electrochemical behaviour of iron in alkaline sulphate solutions

The electrochemical behaviour of pure iron in alkaline sulphate solutions was studied using cyclic voltammetry atT = 298 K. It has been found that the results depend on the polarization pre-treatment of the electrode and the activation state of its surface. At starting potentials in the range of hydrogen evolution and at maximum activation conditions, the voltammograms show three anodic current maxima and two cathodic ones. A correlation between these different maxima is given. The electrode processes, which may take place at these maxima, are discussed in terms of possible iron dissolution mechanisms.     

Silver deposition from its nitrate solutions by hydrogenated palladium

The currentless deposition of Ag⁺ cations from silver nitrate solutions has been found on the surface of hydrogenated Pd (Pd?H). This process has been shown to proceed via a chemico-catalytic mechanism. It has been demonstrated that the major fraction of silver deposited onto the Pd-H system from the nitrate solutions in the first 0.5–1 h of holding in the solution. A minimal size of silver crystallites (26–40 nm) was found when deposited from the diluted nitrate solutions that contain 0.32–2.5 g/L of Ag. The study has revealed that the currentless Ag deposition on the Pd–H surface is accompanied by the formation of the colloid phase of Ag crystallites. It has been established that the Pd–H system could purify solutions of Ag⁺ when the amount of hydrogen in Pd exceeded the amount of Ag⁺ in the solution.     

Hydrogen production during zinc deposition from alkaline zincate solutions

The determination of the amount of hydrogen produced during the electrodeposition of zinc from alkaline zincate solutions was carried out using the rotating ring-disc electrode (RRDE) technique. The experimental conditions for which the RRDE technique offers reliable results are discussed. Hydrogen production during zinc deposition was studied for a range of cathodic (disc) current densities (20–500 A m^–2) and electrolyte compositions (1–7 M KOH, 0.01–0.2 M zincate). It was found that an increasing amount of hydrogen was formed with increasing (disc) current density and decreasing KOH and zincate concentration. The impact of hydrogen formation during the charging process on nickel oxide/zinc secondary battery performance is expected to be small. It is concluded that in battery electrolytes (8 M KOH, 1 M zincate) hydrogen is formed chiefly by corrosion of the zinc electrode rather than by electrochemical formation during the electrochemical reduction of zinc.     

The role of pyrophosphate in copper deposition from cupric pyrophosphate solutions

Cathodic polarization characteristics of copper was examined in cupric pyrophosphate solutions of different concentrations and temperatures. The structure and composition of the deposited copper was examined by scanning electron microscopy, X-ray diffraction, electron probe microanalysis and Auger electron spectroscopy. The polarization characteristics implied that the coverage of the electrode by adsorbed pyrophosphate ions decreases with increasing cathodic polarization and it becomes almost zero past a critical potential E_b of about ?0.75 V vs sce. E_b becomes more negative with increasing concentration of free pyrophosphate ions. As expected, pyrophosphate was incorporated at relatively high concentrations (0.05–0.07 wt% as P) in the deposits in the potential region I (E ? E_b) and at lower concentrations (ca. 0.02 wt%) in region II (E < E_b). Smooth deposits with random crystalline orientations were obtained in a part of region I for cd ? ca. 5 mA/cm². The rough deposits obtained outside this showed preferred (220) orientations as could be expected from the orientation theory. The smooth deposition in region I is due to the pyroposphate adsorption which inhibits the ordered deposition of copper.