Anodic dissolution of aluminium in organic electrolytes containing perfluoroalkylsulfonyl imides

Electrochemical dissolution of aluminium has been investigated in various solutions composed of organic solvents and 1 m lithium bis(perfluoroalkylsulfonyl) imide salts. Potentials of the onset of transpassive dissolution and repassivation as well as dissolution currents have been measured for several systems by using voltammetric methods. Empirical correlation between the composition of the solvent and the dissolution current has been established for mixtures of ethylene carbonate and ethylmethyl carbonate. The effect of the perfluoroalkyl chain length on the dissolution rate has also been studied and the result has been elucidated with the help of considerations on the structure of the ions. Mechanistic information obtained from electrochemical impedance spectra revealed that at least two adsorbed intermediates have to be included in the dissolution mechanism. Conditions of application of lithium perfluoroalkylsulfonyl imides in lithium ion batteries are briefly discussed.     

Influence of some amino acids and vitamin C on the anodic dissolution of tin in sodium chloride solution

The safety of canned foodstuffs should be evaluated not only by recognition of functional foods but also by the presence of toxicants in the human diet. In this study, the anodic dissolution of tin in 3.5% NaCl solution with and without 25–100 mM glycine, serine, methionine, vitamin C and some of their binary mixtures was studied by means of potentiodynamic and impedance techniques. The corroded tin surface was examined by SEM. The results indicated that the passive behaviour of tin is greatly improved by the presence of 50–100 mM glycine and methionine while such improvement is achieved only at 100 mM serine. Both cysteine and vitamin C showed aggressive action. The influence of the glycine/methionine mixture was found to be similar to that of the individual components, whereas the presence of cysteine in the cysteine/methionine mixture annuled the inhibiting action of methionine. The impedance results revealed that the dissolution reaction of tin in NaCl solution with and without glycine, serine and methionine is controlled by the charge transfer process while in the presence of cysteine and vitamin C, the mixed charge transfer and diffusion control is dominant. A rough, bare tin surface was observed in the presence of cysteine and vitamin C while a clean surface covered by corrosion products, in some zones, was observed in NaCl solution containing methionine. © 2001 Society of Chemical Industry     

Initiation of copper dissolution in sodium chloride electrolytes

Initial stages of copper activation in chloride-ion containing neutral aqueous solution were studied. The results point that activation of copper passivity is initiated once the potential exceeds the breakdown value, occurring with well-defined incubation period, similar to that of other passive metals in chloride environments. The effect of applied potential and Cl⁻ ion concentration on the incubation period is presented. The results indicate that an incubation period for copper activation in chloride containing solutions can be associated with the formation of a two-dimensional CuCl layer on the metal surface. The incubation period is relatively long at negative potentials and it is decreases with a positive shift in the potential. At a certain potential, the incubation period is sharply decreased. The time-frame of incubation period is attributed to the formation rate of two-dimensional CuCl layer and its reduction rate. The formation of a stable salt film on the metal surface facilitates localized rapid dissolution of the copper.     

Zinc electrowinning from aqueous chloride electrolytes

Smooth, compact, dendrite-free zinc deposits can be electrowon from acid zinc chloride electrolyte using a diaphragm cell featuring catholyte agitation by air sparging. A correlation exists between the degree of zinc deposition polarization and the zinc deposit structure and orientation that can be used to evaluate the effectiveness of addition agents and, ultimately, to control deposit quality. The effect of impurities on the current efficiency for zinc deposition and on the morphology and orientation of 24h zinc deposits is discussed.     

Electrochemical dissolution and passivation of nickel powder randomly dispersed in a graphite + polypropylene matrix

Nickel powder (10% in weight) randomly dispersed in a graphite (40%) + polypropylene (50%) matrix was studied as a composite electrode in a sulphuric-sulphate acid medium by means of voltammetry and Electrochemical Impedance Spectroscopy (EIS). Under voltammetric conditions, this thermoplastic material shows an electrochemical behaviour similar to nickel metal. However, under EIS measurement conditions the electrodissolution behaviour of the nickel powder is partially limited by the diffusion of the anions in the electrolyte in order to electroneutralize the excess of electrogenerated positive charge. The low frequency range of the measured impedance spectra can be interpreted as a parallel arrangement of a capacitive and a Warburg impedance, instead of a CPE element initially considered in the fitting. Values for CPE exponents lower than 0.85 are interpreted as a competition between a capacitive/transport contribution to the overall impedance response.     

On two control parameters of the dynamics of the anodic dissolution of copper

An experimental study of the effect of SCN⁻ ion concentration and laser bombardment intensity on the anodic dissolution of copper into an aqueous NaCl electrolyte is reported. The laser was used to accelerate the dissolution process. The results are analyzed in terms of power spectra, fractional Brownian motion theory and confocal image processing. An interpretation of the dynamic phenomena via the theory of nonlinear dynamics is also suggested.     

An application of queuing theory to the dynamics of anodic dissolution

Queuing theory is applied to oscillatory phenomena encountered during anodic dissolution, with numerical illustration provided by a laboratory-scale copper dissolution process. The theory interprets oscillation as a two-phase process, where the first phase consists of ion arrival to the electrode and subsequent steps to form a solid deposit on it, and the second phase consists of the deposition process itself followed by partial dissolution of the deposit. The two phases correspond to the process of client-arrival and client-servicing in queuing theory. In particular, the M/M/1, the G/M/1 and the M/M/k queuing models are quantitatively compared in terms of queuing time and certain other queuing characteristics.     

化学镀Ni－Mo－P合金阳极溶解行为的XPS研究

利用ＸＰＳ等手段研究了化学镀Ｎｉ－Ｍｏ－Ｐ合金在Ｈ＿２ＳＯ＿４溶液中的阳极溶解行为。结果显示，稳定电位下阳极形成稳定致密的钝化膜，其主要成分为Ｎｉ（ＯＨ）＿２，其余为Ｎｉ（ＰＯ＿４）＿２、ＭｏＯ＿２及部分结合水。阳极电位正移，阳极表面膜厚度增加，结合水减少，在０．２Ｖ左右，阳极溶解电流剧增，局部腐蚀严重。此时，表面膜的主要成分为Ｎｉ＿３（ＰＯ＿４）＿２，其余为Ｎｉ（ＯＨ）＿２及ＭｏＯ＿２。合金在阳极溶解过程中出现磷（钼）在合金的富集。     

Effect of nitrite anions on the rate of iron dissolution in acid electrolytes

The effect of the concentration of nitrite ions, potential, pH and solution stirring on the dissolution rate of iron was studied. Nitrite ions were shown to accelerate active dissolution. The accelerating action of the oxidant depends on the ratio of the rates of electroreduction at the electrode surface and homogenous chemical reduction in the reaction layer adjacent to the electrode. A possible mechanism of oxidant action on the iron dissolution is considered. The electroreduction process is assumed to generate at the iron surface an activated complex accelerating metal dissolution.     

Electrochemical behaviour of the antimony electrode in sulphuric acid solutions—I. Corrosion processes and anodic dissolution of antimony

The corrosion processes at open circuit conditions and in the active dissolution region of antimony, at low anodic overpotentials, have been studied in sulphuric acid solutions. It was established that antimony dissolution at open circuit is coupled to oxygen reduction, which occurs via the hydrogen peroxide route. The rate of antimony dissolution was found to increase linearly with increasing acid concentration. Based on potentiodynamic, galvanodynamic and steady-state measurements as well as ac impedance data possible mechanisms for the corrosion processes at open circuit as well as for the dissolution of antimony in the active region are proposed and discussed.     

A study of the dynamics of anodic copper dissolution in a NaCl/KSCN electrolyte

The oscillatory behaviour of the anodic dissolution of copper into an aqueous NaCl solution containing a small amount of thiocyanate ions has been studied experimentally in the absence and in the presence of a magnetic field. The latter has an inhibiting effect on the oscillation and, under specific conditions, it can fully suppress it.     

Production of nanoparticles of copper compounds by anodic dissolution of copper in organic solvents

The anodic behaviour of copper was investigated in ethanol solution containing LiClO₄, LiCl electrolyte and water. The type of electrolyte and the water content influences the mechanism of the anodic process and the formation of anodic products. In LiClO₄ electrolyte the dissolution of copper is related to the oxidation of Cu(I) to Cu(II). In solutions of LiCl the etching of copper begins with the creation of soluble complexes of Cu(I) with chloride ions and solvent molecules. At potentials above 0.4 V the formation of alkoxides was observed in both solutions, characterized by a yellow tint. On the other hand, above 0.8 V (i.e. above the equilibrium potential of alcohol oxidation) copper dissolution is accompanied by the formation of a blue colloidal suspension of Cu (II) copper salt. Anodic etching of copper in solutions containing 3% H₂O at potentials higher than 0.4 V leads to the formation of colloidal suspension of copper oxide nanoparticles.     

An electrochemical study of the dissolution of gold in thiosulfate solutions Part I: Alkaline solutions

The anodic dissolution of gold in alkaline thiosulfate solutions has been studied by using a rotating gold disc. Experimental results have shown that the gold dissolves at measurable rates in thiosulfate solutions at potentials above 0.2 V. It has been confirmed that dissolution occurs in parallel with oxidation of thiosulfate with a dissolution current efficiency that varies with time and with the experimental conditions and which is generally in the range of 0.3 to 0.6. Although oxygen could be used as an oxidant for gold in the thiosulfate system, the rate of the cathodic reduction of oxygen in the relevant potential region is too slow for practical purposes. It was found that in the potential region investigated, thiosulfate ions undergo oxidative decomposition leaving a sulfur-like film on the surface of gold, which inhibits the rate of dissolution of gold and results in a low anodic current efficiency for the dissolution of gold. The factors (temperature, pH, thiosulfate concentration and ammonia) have been found to have positive effects on the kinetics of gold dissolution. The rates of gold dissolution in oxygenated alkaline thiosulfate solutions have been estimated to be much lower than in the copper–ammonia–thiosulfate and cyanide systems.     

An electrochemical study of the dissolution of gold in thiosulfate solutions. Part II. Effect of Copper

Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper–thiosulfate–oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions.     

Zinc barrel electroplating using low cyanide electrolytes

The influence of plating conditions on the cathode efficiency of zinc barrel electroplating and the quality of deposited layers for low cyanide electrolytes is analysed. The investigations are carried out using factorial design methodology. The first part of the study shows how electrolyte components, such as brightening agent, sodium carbonate concentration, sodium hydroxide concentration, sodium cyanide concentration and zinc metal content, influence cathode efficiency and the morphology and the texture of the zinc electrodeposits. A mathematical model that fits experimental data is suggested and the pseudo three-dimensional plot of yield as a function of electrolyte composition for three significant component mixtures, brightening agent, sodium cyanide concentration and zinc metal content, is represented. The second part of the study shows how varying six process parameters influences current efficiency and metal thickness distribution. For the range studied, efficiency is affected by workload volume, current density, perforation and part size, but not by rotation speed and quantity of charge.     

Neutralization of used Li batteries: Anodic dissolution of the iron–nickel alloy positive pins of Li–SOCl2 batteries in seawater

This paper reports a study of the neutralization of Li–SOCl₂ batteries. Immersion of these batteries in acidic seawater solutions leads to their complete discharge by short circuit, followed by corrosion of the positive pin (made of an Fe/Ni alloy). This corrosion process is desirable because it allows penetration of water into the battery, and hence, neutralization of the active mass of the batteries through their reaction with water. The most efficient corrosion of Fe/Ni electrodes is obtained in seawater containing both HCl and H₂SO₄ in a situation of no separation between the electrode compartments, due to the reaction of the H₂ liberated at the cathode with the surface films on the anode (Fe/Ni pin electrodes). This reaction prevents passivation of the positive pin. Indeed, used Li–SOCl₂ batteries whose insulating covers were removed, corroded much quicker than regular batteries because of the impact of H₂ evolved at the case (the negative pole of the battery) on the dissolution of the positive pin.     

Burning of a Cotton Fabric Impregnated by Synthetic Zinc Carbonate Hydroxide as a Flame Retardant

Zinc carbonate hydroxide [ZnCO₃·Zn(OH)₂] synthesized by means of the multiple-bath method was deposited onto a cotton fabric, and its uniformity was ensured by means of squeeze rolls. Prolonged burning was observed on treated specimens: 200.5 sec for 20.20% of ZnCO₃·Zn(OH)₂ added to 100 g of a dry fabric increased to 337.5 sec for a 45.39% addition. The ashes of the treated specimens were subjected to X-ray diffraction analysis, and the result was compared with data for zinc and zinc-oxide powders. The existence of zinc oxide was detected in the ashes, but no traces of the metallic zinc were discovered. Therefore, it can plausibly be assumed that a reduction-oxidation reaction occurs during the smoldering process.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 73–77, July–August, 2005.     

The anodic dissolution of 90% copper-10% nickel alloy in hydrochloric acid solutions

The anodic dissolution of the 90% copper-10% nickel alloy in hydrochloric acid solutions at the rotating disk was found to be controlled by both mass transfer and reaction in the apparent Tafel region. The kinetics of dissolution are similar to those of pure copper for the partial currents due to the dissolution of both the copper and nickel components from the alloy. A mechanism for the dissolution of the alloy is proposed. This mechanism describes the dissolution as being controlled by the dissolution of the copper from the alloy. In the limiting-current region a film of CuCl precipitates on the surface of the electrode. The reaction in the limiting-current region is controlled by mass transfer. A mechanism which describes the precipitation and dissolution of this film, and which describes the diffusion of the chloride to the surface of the electrode is proposed.     

Quantitation of the dissolution of battery-grade copper foils in lithium-ion battery electrolytes by flame atomic absorption spectroscopy

Atomic absorption spectroscopy (AAS) was shown to be an effective method to quantitatively evaluate the stability of battery-grade copper foils in lithium-ion battery electrolytes at open-circuit. The results showed that copper stability was different between “fresh” electrolyte and electrolytes that had been “aged” for 6 months. In the “fresh” electrolyte, the copper foils showed a small amount of dissolution (up to ∼50 ppm) during their storage for up to 20 weeks. In the “aged” electrolyte, a large amount of copper dissolution (up to several hundred ppm) was found. The study showed that the condition of the electrolytes was critical to the stability of the copper foils.     

Kinetics of the dissolution of silica in aqueous sodium hydroxide solutions at high pressure and temperature

The kinetic of the reaction of sand with aqueous NaOH corresponding to the ratio SiO₂/Na₂O = 2 was studied in a pressure vessel at 220°C and 2.7 MPa. Since the kinetic curves could not be obtained directly from the experimental data, a new method is proposed to plot the entire kinetic graph from experimental data. An analytical expression of the type α = A [1 -exp(-Bt)] describes the system perfectly. The constants A and B were calculated for a silica sample having a narrow granulometric distribution (range i.e. 300–315 μm). The value of A is found to be almost constant, between 0.95 to 0.99 and B ranges from 0.03 to 0.14 when [OH-] increases from 0.5 to 12.5 mol/L. The kinetic order with respect to OH^? is equal to 0.470 + 0.013 and the kinetic constant at 220°C is 3.933 × 10^?6 g/m².s.