Showing papers in "Journal of Applied Electrochemistry in 1991"
TL;DR: In this article, the electrochemical oxidation of phenol for waste water treatment was studied at a platinum anode, and the reaction occurs by two parallel pathways; chemical oxidation with electrogenerated hydroxyl radicals and direct combustion of adsorbed phenol or/and its aromatic intermediates to CO2.
Abstract: The electrochemical oxidation of phenol for waste water treatment was studied at a platinum anode. Analysis of reaction intermediates and a carbon balance has shown that the reaction occurs by two parallel pathways; chemical oxidation with electrogenerated hydroxyl radicals and direct combustion of adsorbed phenol or/and its aromatic intermediates to CO2.
603 citations
TL;DR: In the search for a DSA®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO2, RuO2, Pt as conducting component, and TiO2 and Ta2O5 as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability.
Abstract: In the search for a DSA®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO2, RuO2, Pt as conducting component, and TiO2, ZrO2, Ta2O5 as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability. Electrochemical “true” surfaces of the coatings were found to be dependent on structure and morphology: the mixtures that form a solid solution (RuO2−TiO2), or allow limited miscibility (IrO2−TiO2), show the lowest dispersion of active material. Differences in service lives, were attributed to differences in wear mechanism of the electrodes. It was found that Ti/IrO2 (70 mol%)-Ta2O5 (30 mol%) is by far the best electrode.
389 citations
TL;DR: In this paper, the performance of SnO2 as an anode material with high oxygen gas-evolution overpotential was investigated in view of its application for electrochemical oxidation of bio-refractory organics in waste waters.
Abstract: The electrochemical performance of SnO2 as an anode material with high oxygen gas-evolution overpotential was investigated in view of its application for electrochemical oxidation of bio-refractory organics in waste waters. The influence of the doping agent (Sb, F, Cl) and doping level on the oxygen-evolution reaction was studied in terms of Tafel slope, oxygen-overpotential and exchange current densities for the Ce3+→Ce4+ reaction. Tafel slopes of about 300 mV decade−1 were found and the oxygen evolution overpotential was 600mV higher than that of platinum. While the doping level had no significant influence on Tafel slopes and oxygen overpotentials the stability of the SnO2 electrode increased with charge carrier density. The oxidation of phenol was investigated as a test for the oxidizing power of the new anode material when compared to Pt or PbO2. The rate of phenol removal was much higher for SnO2 than for PbO2 or Pt.
339 citations
TL;DR: In this article, the performance of highly doped SnO2 anodes for the oxidative treatment of biologically refractory waste water was compared with PbO2 and Pt.
Abstract: The performance of highly doped SnO2 anodes for the oxidative treatment of biologically refractory waste water was compared with PbO2 and Pt. The oxidation of a wide range of organic compounds proceeds with an efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the water. In chloride containing media, SnO2 anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO2 anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by mass transfer, indicating the participation of homogeneous reactions in the overall oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50 kWh kg−1 of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or wet oxidation using oxygen at elevated temperature and pressure.
301 citations
TL;DR: In this article, the most important effects of additives, such as the grain refinement of the deposit, polarization of the cathode, incorporation of additives in the deposit and the change of the orientation of crystals and the synergism of additives are presented.
Abstract: This review concerns fundamental aspects of levelling and brightening in the electrodeposition of metals. The most important effects of additives, such as the grain refinement of the deposit, polarization of the cathode, incorporation of additives in the deposit, the change of the orientation of crystals and the synergism of additives are presented. The mechanisms proposed to explain the action of additives in metal electrodeposition are classified taking into account the rate determining step of the process. The main mechanisms are discussed.
279 citations
TL;DR: In this paper, several DSA® coatings were prepared by thermal decomposition of metallic chloride salts on titanium base and it was shown that the painting composition does not necessarily correspond to the final coating composition.
Abstract: Several DSA® coatings were prepared by thermal decomposition of metallic chloride salts on titanium base. It was shown that the painting composition does not necessarily correspond to the final coating composition. Thermogravimetric and fluorescent X-ray measurements were used to identify and characterize the material losses. It was found that IrO2, Ta2O5 and RuO2 compounds can be deposited with almost 100% yield, while SnO2 and Pt precursors give high material losses. The influence of parameters affecting the deposition yield are discussed.
159 citations
TL;DR: In this article, the effect of interrupted current (pulsed) electrolysis on the generation of gas bubbles is investigated. And a mechanism based on local potential gradients is proposed to explain this phenomenon.
Abstract: Fine bubbles of the size required for many processes such as electroflotation can be generated by electrolysis. A large number of factors such as electrode material, electrode surface/morphological properties, pH and current density affect the gas bubble size distribution. This work is aimed at studies on the effect of interrupted current (pulsed) electrolysis on the generation of gas bubbles. A microcomputer-controlled current source designed to generate the required pulses is described along with typical results obtained with this system. It was observed that a decrease in duty cycle at a given pH and average current density causes an increase in fine sized bubbles and concomitant increase in bubble flux. A mechanism based on local potential gradients is proposed to explain this phenomenon.
119 citations
TL;DR: In this paper, the mass transport properties of reticulated vitreous carbon cathodes, operated in the flow-by mode, were characterized using current-potential curves recorded at a rotating retriculated carbon disc electrode to determine the diffusion coefficient for copper(II) under the conditions of the experiments.
Abstract: The cathodic deposition of copper from acid sulphate solution containing copper(II) has been used to characterize the mass transport properties of reticulated vitreous carbon cathodes, operated in the flow-by mode. Current-potential curves recorded at a rotating vitreous carbon disc electrode were used to determine the diffusion coefficient for copper(II) under the conditions of the experiments and also to elucidate the effect of oxygen in the electrolyte stream. Pressure drop measurements have been used to separate the mass transport coefficient and real surface area effect for four grades of reticulated vitreous carbon, nominally having 10, 30, 60, 100 pores per inch.
104 citations
TL;DR: In this paper, the performance of PEM fuel cells and the morphology of low-catalystloading electrodes were investigated, taking into account the thickness of the catalyst layers, the crystallite sizes of the platinum electrocatalyst supported on carbon and the increased Pt catalyst content near the front of the electrodes.
Abstract: This paper describes the results of transmission electron microscopic, scanning electron microscopic and/or Rutherford backscattering spectroscopic analyses of platinum electrocatalysts supported on carbon, and of low catalyst loading gas-diffusion electrodes used in proton-exchange-membrane (PEM) fuel cells. We looked for correlations between the performance of PEM fuel cells and the morphology of low-catalyst-loading electrodes, taking into account the thickness of the catalyst layers, the crystallite sizes of the platinum electrocatalyst supported on carbon and the increased Pt catalyst content near the front of the electrodes. We reached the conclusion that the use of electrodes with thin catalyst layers (made by using platinum on carbon electrocatalysts with a high Pt/C weight ratio) and with more platinum localized near the front surface had the effect of diminishing the overpotentials in PEM fuel cells.
95 citations
TL;DR: The main factors influencing the morphology of solid metal obtained at the cathode of an electrolytic cell are discussed in this paper, where specific topics linked to electrogalvanizing are stressed.
Abstract: In this paper, the main factors influencing the morphology of solid metal obtained at the cathode of an electrolytic cell are discussed. Although the presentation is rather fundamental, important practical conclusions are derived. Specific topics linked to electrogalvanizing are stressed.
90 citations
TL;DR: In this article, the electrodeposition of copper, gold, nickel, palladium and platinum onto Ebonex® ceramic cathodes has been studied and it was demonstrated that good quality deposits may be obtained and that the kinetics of the deposition and dissolution of metals are similar at Eboneix® to other common substrates (for example, Pt, C) in addition, the kinetic of some simple redox couples at coated and bare Eboneis® ceramic electrodes are compared; it is confirmed that such electron transfer reactions are very slow on the bare Ebonex
Abstract: The electrodeposition of copper, gold, nickel, palladium and platinum onto Ebonex® ceramic cathodes has been studied It is demonstrated that good quality deposits may be obtained and that the kinetics of the deposition and dissolution of metals are similar at Ebonex® to other common substrates (for example, Pt, C) In addition, the kinetics of some simple redox couples at coated and bare Ebonex® ceramic electrodes are compared; it is confirmed that such electron transfer reactions are very slow on the bare Ebonex® ceramic but when the surface is coated with a metal, the kinetics are similar to those on the bulk metal
TL;DR: In this paper, the properties of a carbon felt electrode have been experimentally investigated with special attention to its possible application in the electrochemical recovery of heavy metals, by means of the reduction of ferricyanide and cupric ions for a flow-by electrode operating under limiting current conditions.
Abstract: The properties of a carbon felt electrode have been experimentally investigated with special attention to its possible application in the electrochemical recovery of heavy metals. The mass transfer process has been studied by means of the reduction of ferricyanide and cupric ions for a flow-by electrode operating under limiting current conditions. An empirical correlation between the Sherwood and Reynolds numbers has been used to compare the experimental data with those obtained by other authors for different porous electrodes.
TL;DR: In this article, X-ray photoelectron spectroscopic (XPS) and electrochemical techniques have been applied to the investigation of surface oxidation of synthetic heazlewoodite (Ni3S2).
Abstract: X-ray photoelectron spectroscopic (XPS) and electrochemical techniques have been applied to the investigation of the surface oxidation of synthetic heazlewoodite (Ni3S2). The XPS data showed that exposure of the sulphide to air resulted in nickel atoms migrating to the surface to form an overlayer of a hydrated nickel oxide and leave a sulphur-rich heazlewoodite. A hydrated nickel oxide was also produced on immersion of heazlewoodite in acetic acid solution in equilibrium with air, despite nickel being soluble under these conditions. After the acetic acid treatment, the S(2p) spectrum had a component at the binding energy of NiS and a small contribution due to sulphur-oxygen species. Voltammetry with bulk heazlewoodite electrodes, and the ground sulphide in a carbon paste electrode, indicated that, at pH 4.6, the initial anodic product was a sulphur-rich heazlewoodite and that oxidation was inhibited when NiS was formed on the surface. Further oxidation to higher nickel sulphides and elemental sulphur occurred at high potentials. In basic solutions, oxidation was restricted due to the formation of nickel oxide.
TL;DR: In this paper, the corrosion behavior of zinc-nickel alloy coatings of various thicknesses and different compositions in the chromated and non-chromated condition on steel was discussed.
Abstract: Improved corrosion resistance requirements, higher production costs and stringent pollution regulations have led researchers and commercial platers to study and develop new types of coatings for protection of steel components. Deposition of zinc-nickel alloy is of particular interest to the automobile industry where the coatings should satisfy many vital requirements such as formability, weldability, paint adhesion. This paper discusses the corrosion behaviour of zinc-nickel alloy coatings of various thicknesses and different compositions in the chromated and non-chromated condition on steel. The corrosion resistance was tested by various electrochemical methods and an industrially adopted salt spray test and the results indicate that an alloy deposit containing 15–18% nickel can efficiently replace zinc and cadmium deposits.
TL;DR: In this paper, the performance of reticulated vitreous carbon cathodes for the removal of low levels of copper ions from aqueous, acidic sulphate media is described.
Abstract: The performance of cells with reticulated vitreous carbon cathodes for the removal of low levels of copper ions from aqueous, acidic sulphate media is described. During the batch recirculation of nitrogen-sparged, sodium sulphate solutions, pH 2, the copper ion concentration may be reduced from 10 p.p.m. to <0.5 p.p.m. or from 2.5 p.p.m. to <0.1 p.p.m. with overall current efficiencies of 84% and 42%, respectively. The influence of solution flow rate through the cathode and the choice of the grade of the reticulated carbon is discussed. The removal of copper ions from solutions of low ionic strength, saturated with air and/or containing chloride ion is also investigated.
TL;DR: In this paper, the authors characterized the compounds grown on copper during oxidation at low temperature (T <573 K) in air by electrochemical and optical methods, and established the mechanism of reduction for layers containing CuO and a non stoichiometric copper(I) oxide.
Abstract: The aim of this study was to characterize the compounds grown on copper during oxidation at low temperature (T<573 K) in air by electrochemical and optical methods. The following oxides have been characterized: a precursor Cu
x
O of mixed valency character, a non stoichiometric cuprous oxide, CuO and its precursor. The mechanism of reduction has been established for layers containing CuO and a non stoichiometric copper(I) oxide. CuO is reduced before cuprous oxide. In complicated cases, it is impossible to draw conclusions from the characteristics of the electrochemical reduction (the first step of CuO reduction and the reduction of Cu(I) species specific of the non-stoichiometry are observed at the same potential). Nevertheless, the association of a non-destructive technique such as diffuse reflectance spectroscopy and electrochemical methods allows identification of the different species present in corrosion layers on copper surfaces.
TL;DR: In this paper, mixed oxide coatings of tin and iridium oxide on titanium substrates have been studied over the composition range of 5 to 100 mol % iridium oxides.
Abstract: Mixed oxide coatings of tin and iridium oxide on titanium substrates have been studied over the composition range of 5 to 100 mol % iridium oxide. While stannic oxide behaves as a simple diluent for the electrocatalytically active precious metal oxide, substantial replacement of iridium by tin may be made with little degradation of coating performance in oxygen evolution.
TL;DR: A model of an “acid” and an "alkaline” state of the membrane has been developed, which can be applied both for cation and anion exchange membranes, which is a valuable help in optimizing the concentrations of sodium sulphate, sulphuric acid and caustic soda.
Abstract: There is an increasing interest in the electro-chemical splitting of sodium sulphate into caustic soda solution and sulphuric acid by means of ion exchange membranes. Adaptation of the product properties to the demands of recycling requires the use of cation exchange membranes, anion exchange membranes or a combination of both. Application of available membranes results in product concentrations which are below usual industrial standards. Extensive measurements prove that the current efficiency is either dependent on concentrations of the anode region (sulphuric acid, sodium sulphate) or on the concentrations of the cathode region (caustic soda, sodium sulphate) with regard to the range of concentrations. In order to explain these phenomena a model of an “acid” and an “alkaline” state of the membrane has been developed, which can be applied both for cation and anion exchange membranes. This model is a valuable help in optimizing the concentrations of sodium sulphate, sulphuric acid and caustic soda.
TL;DR: In this paper, the effect of substituting SnO2 for TiO2 in RuO2+TiO2 electrodes has been studied by varying the SnO 2 content systematically in a series of oxides of general composition 30 mol% RuO 2+x mol% Sn O2+(70-x) mol% TiO 2.
Abstract: The effect of substituting SnO2 for TiO2 in RuO2+TiO2 electrodes has been studied by varying the SnO2 content systematically in a series of oxides of general composition 30 mol% RuO2+x mol% SnO2+(70-x) mol% TiO2. The surface properties have been investigated by voltammetric curves, the electrocatalytic activity by using O2 evolution from 1 mol dm−3 HClO4 solutions as a test reaction. It has been observed that only the surface area changes at intermediate compositions as a result of morphological modifications, while the electrocatalytic activity increases dramatically as the substitution of SnO2 for TiO2 becomes complete. Reasons for that are discussed. The present results do not support the claim that SnO2 depresses the electrocatalytic activity of oxide electrodes for oxygen evolution.
TL;DR: In this article, the anode and cathode potentials in a single cell with twenty-four reference electrodes located around anode or the cathode were studied under starving conditions for either air or fuel.
Abstract: The changes in the anode and cathode potentials in the horizontal plane of a phosphoric acid fuel cell (PAFC) under starving conditions for either air or fuel were studied using a single cell furnished with twenty-four reference electrodes which were located around the anode or the cathode. When air starvation occurred, both the anode and cathode potentials became nearly 0 V against RHE, and hydrogen generation began to occur on the cathode side. Fuel starvation occurred when fuel utilization became more than 95%, and the cathode potential in the fuel outlet area shifted significantly toward the positive and, simultaneously, CO and CO2 were detected in the air exhaust gas, indicating the occurrence of carbon corrosion of the cathode components. By further increasing the fuel utilization, the cell voltage changed to negative and the anode potential in the fuel outlet area became the highest. At that time, significant amounts of CO and CO2 were detected in the fuel exhaust gas, indicating the occurrence of carbon corrosion of the anode components. Immediately after the termination of fuel starvation, the cathode potential in the fuel outlet area shifted quickly and remarkably toward the positive, and exceeded 1 V against RHE in a few seconds.
TL;DR: In this paper, the continuous removal of toxic hexavalent chromium from contaminated solutions by means of a graphite felt based electrochemical column was studied, and conditions for the attainment of low (<25 p.p.b.) effluent concentrations as well as longitudinal concentration distribution of the precipitate and maximum loading capacities were presented.
Abstract: The continuous removal of toxichexavalent chromium from contaminated solutions by means of a graphite felt based electrochemical column was studied. The process is based on anin situ generation of appropriate pH gradients which allows both rapid reduction to Cr3+ and its precipitation within the electrode bed. Conditions for the attainment of low (<25 p.p.b.) effluent concentrations as well as longitudinal concentration distribution of the precipitate and maximum loading capacities are presented. Treatment schemes involving two separate columns or a dual function column are also discussed.
TL;DR: In this article, the PAR M342C Softcorr Corrosion Software, devised for computing corrosion currents, was used to measure the leaching rate of gold, silver, palladium and platinum in cyanide solutions.
Abstract: The leaching rates of gold, silver, palladium and platinum in cyanide solutions have been determined from the corrosion potential and voltammograms of the anodic oxidation reaction. The order of reactivity was Au>Ag>Pd>Pt and the leaching rate was a maximum at about pH 10 for each metal. An assessment was made of the applicability of PAR M342C Softcorr Corrosion Software, devised for computing corrosion currents, to the measurement of leaching rates of precious metals. The software does not yield accurate rates due to the nature of the individual oxygen reduction and metal dissolution processes, but could be applied to rapidly estimate the influence of variation in solution composition on the leaching of an individual metal.
TL;DR: In this article, the anodic oxidation of tin in 0.1 to 1M bicarbonate solutions at pH 8 has been studied, and the process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity.
Abstract: The anodic oxidation of tin in 0.1 to 1M bicarbonate solutions at pH 8 has been studied. The process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity. The rate-determining step of the reaction in the active-dissolution region is attributed to the diffusion of an ionic species into the solution, the diffusing species being generated at the metal surface. In the region of the first oxidation peak, the reaction rate is controlled by diffusion of CO
3
2−
species in solution. When the potential becomes more positive than −0,1 Vsce, a highly passivating (most likely SnO2) film is formed on the electrode surface.
TL;DR: In this paper, an electrochromic device consisting of a cathodically colouring tungsten trioxide (WO3) film, an anodically coloured Prussian blue (PB) film and a polymer electrolyte was made.
Abstract: Optically variable windows (smart windows), which control the transmission of light into buildings and vehicles, are of interest both for the control of solar heat load and for privacy applications Such windows are likely to utilize electrochromic technology to achieve optical control An electrochromic device consisting of a cathodically colouring tungsten trioxide (WO3) film, an anodically colouring Prussian blue (PB) film, and a polymer electrolyte was made The polymer electrolyte was prepared from polyvinyl alcohol doped with H3PO4 and KH2PO4 to accommodate the conduction of both H+ and K+ ions The electrochromic WO3 and PB films functioned in a complementary way such that the device was coloured or bleached by the application of −05 V or +05 V (WO3 films vs PB film), respectively The spectral characteristics of the coloured device confirmed the complementary colouration of WO3 and PB in the device
TL;DR: In this article, a hypochlorite cell divided by an anionic membrane was examined, and it was shown that it is possible to suppress cathodic reduction of hypochchlorite and to achieve a higher degree of chloride-to-hydrogen conversion, at relatively high current efficiencies, than in the case of an undivided cell, using seawater or untreated diluted brine electrolyte.
Abstract: A hypochlorite cell divided by an anionic membrane was examined. The results clearly show that it is possible to suppress cathodic reduction of hypochlorite and to achieve a higher degree of chloride to hypochlorite conversion, at relatively high current efficiencies, than in the case of an undivided cell, using seawater or untreated diluted brine electrolyte.
TL;DR: In this article, it was shown that adding 0.1 to 0.4% PGMs to chromium in sulphuric acid caused the alloy to self-passivate easily and also increased the corrosion resistance by several orders of magnitude.
Abstract: The truly remarkable corrosion resistance of alloys containing small amounts of noble metals relies on the principle that the high exchange-current density for the reduction of hydrogen can shift the corrosion potential of the alloy to a value in the passive region, causing it to passivate spontaneously. Research indicates that additions of 0.1 to 0.4% PGMs to chromium in sulphuric acid cause the alloy to self-passivate easily and also increased the corrosion resistance by several orders of magnitude. The effectiveness of the PGMs in promoting corrosion resistance was found to decrease in the order Pt>Pd>Ir>Ru>Os. An enrichment of PGMs at the surface of the alloys occurred during the period of active dissolution. The effect of cathodic additions in ferritic stainless steels became more enhanced with an increase in the chromium content of an alloy. Furthermore, if molybdenum and a PGM occur together in an alloy, a synergistic beneficial effect is exerted on the corrosion resistance. The effect of the cathodic modification of austenitic stainless steels is not as dramatic as for ferritic stainless steels. Little is known about the effect of PGMs on the corrosion behaviour of duplex stainless steels. Work on titanium-palladium alloys led to the development of a commercial titanium-palladium alloy containing 0.2% palladium, which is especially suited to reducing conditions. By contrast with the chromium and stainless-stell alloys, the addition of PGMs to titanium was found not to be detrimental to its corrosion resistance in highly oxidizing media. The surface alloying of materials with PGMs by various methods could prove to be a more cost-effective method than bulk alloying.
TL;DR: In this paper, the passivation behavior of α-brass (Cu∶Zn=67∶33) in alkaline solutions was studied using cyclic voltammetry and potentiostatic current transient measurements.
Abstract: The passivation behaviour of α-brass (Cu∶Zn=67∶33) in alkaline solutions was studied using cyclic voltammetry and potentiostatic current transient measurements. The recorded cyclic voltammograms exhibited the main features usually observed for pure copper and zinc, and one additional anodic peak on the reverse potential scan. The height, sharpness and location of the different peaks depended greatly on the alkali concentration and the scan rate. The results show that the formation of Cu2O and Cu(OH)2 films proceed under ohmic resistance control following a dissolution-precipitation mechanism. The effect of F−, Cl− and Br− ions on the passivity was also studied. The pitting potential was found to decrease with logarithm of halide ion concentration. The current transients in the absence and presence of halide ions were analysed. In the absence of pitting the current, after a few seconds, was found to increase linearly with the reciprocal of the square root of time while in the presence of pitting it was found to fit the Engell-Stolica equation.
TL;DR: In this paper, the electrocatalytic hydrogenation of benzene, aniline, and nitrobenzene at a Raney nickel powder cathode was investigated at a single phase electrolyte consisting of t-butanol, water, and a hydrotropic salt, either sodium or tetraethylammoniump-toluenesulphonate (TEATS).
Abstract: The electrocatalytic hydrogenation of benzene, aniline, and nitrobenzene was investigated at a Raney nickel powder cathode. The single phase electrolyte consisted of t-butanol, water, and a hydrotropic salt, either sodium or tetraethylammoniump-toluenesulphonate (TEATS). The hydrogenation of benzene was achieved only in the latter case; the only product detected was cyclohexane. The highest current efficiency (73%) was obtained at 50° C, 1.0m benzene, 2.5m TEATS, and at an apparent current density of 4.0 mA cm−2. Aniline was electrocatalytically hydrogenated to cyclohexylamine only in the presence of a quaternary ammonium ion supporting electrolyte (containing either Br− orp-toluenesulphonate anions), with product current efficiencies of ∼40%. When nitrobenzene was hydrogenated with a sodiump-toluenesulphonate supporting electrolyte, only nitro group reduction was observed. When the supporting electrolyte was TEATS, both nitro group reduction and aromatic ring hydrogenation occurred.
TL;DR: In this article, the electroplating of zinc-nickel alloys from a chloride bath containing two brighteners (a phenolic derivative and an unsaturated aromatic compound) and a levelling agent (an aromatic carboxylate) has been studied under different plating conditions.
Abstract: The electroplating of zinc-nickel alloys from a chloride bath containing two brighteners (a phenolic derivative and an unsaturated aromatic compound) and a levelling agent (an aromatic carboxylate) has been studied under different plating conditions. The composition and morphology of the alloys depended on the concentration of all the additives and also on the temperature. As a general effect, these additives smooth the deposit and refine the grain size. By means of scanning electron microscopy, it was possible to classify the deposit morphologies according to the type and concentration of the additives. The resistance of the alloys to corrosion was studied by means of a neutral salt-spray test.
TL;DR: In this article, the effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments, and it was shown that aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH.
Abstract: The effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments. The solution chemistry of aluminium, zinc, and iron in aqueous solution in the absence and in the presence of fluoride ions was studied with the construction of the Eh-pH diagrams for the Al−F−H2O, Zn−F−H2O and Fe−F−H2O systems at 25°C. In the presence of fluoride ions, aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH whereas zinc and iron can form soluble or insoluble metal-fluoride complex species only at relatively high fluoride concentration and at higher pH values. Experimental results show that in the presence of fluoride ions, the corrosion of pure aluminium in sulphuric acid is due to uniform dissolution and the reaction rate depends on the fluoride concentration. In zinc electrolyte containing fluoride ions, zinc deposits onto the pure aluminium substrate spontaneously and the amount of deposited zinc also depends on the fluoride concentration. On the other hand, the presence of iron in the Al−Fe alloy accelerates the corrosion of aluminium in H2SO4 and zinc electrolyte significantly and prevents the deposition of zinc on the aluminium surface. The effect of fluoride ions on zinc adherence to the aluminium is also discussed.