Anodic Dissolution of Nickel from the Individual and NiZn Intermetallic Phases in Acidic Sulfate Solutions. II. NiZn Intermetallic Compound

Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former.     

A Refined Scheme of the Mechanism of Iron Anodic Dissolution in Acidic Sulfate Solutions

A refined scheme of iron anodic dissolution in acidic sulfate solution, in which Fe₀ is oxidized to Fe⁺ in stages, is proposed. The first stage consists in chemisorption of H₂O molecules with participation of SO₄ ^2– anions; the degree of the participation x 0.5 per a water molecule. This stage produces adsorbed OH groups (Fe(OH)_ads), which, as a result of their interaction with sulfate anions, form an adsorption complex Fe((OH)SO₄ ^2– _ads. The schemes of oxidation of Fe⁺ to Fe²⁺ do not differ from conventional ones. The scheme put forward agrees with the literature data on the kinetics of iron dissolution under steady-state conditions.     

The First-Stage Kinetics of the Iron Anodic Ionization in Acidic Sulfate Solutions

The hypothesis that water molecules are involved in the anodic dissolution of iron in acidic sulfate solutions is confirmed experimentally. The oxidation of Fe⁰ iron to Fe⁺ is shown to proceed in stages: at the first stage, the interaction between the metal and water molecules results in the formation of surface charge-transfer complexes, which then decompose to form the adsorbed OH groups. The charge transfer in the complexes is estimated to be about 0.5.     

Kinetic Regularities of Nickel Anodic Dissolution in Water–Alcohol Sodium Chloride Solutions

Nickel anodic dissolution in water–alcohol sodium chloride solutions is studied on a rotating disk electrode. It is found that the character of the limiting stage of nickel dissolution is determined by the essence of the alcohol. Under potentiostatic conditions, a spontaneous increase in the current (autocatalytic effect) is found, which depends on the solution composition.     

Reduction of Nickel by Hydrogen from Ammoniacal Nickel Sulfate Solutions

This paper is an account of a detailed examination of the reaction by which nickel can be precipitated from aqueous ammoniacal nickel sulfate solutions by hydrogen at elevated pressures and temperatures. The thermodynamics of the reactions are discussed and the behavior of ammonia is illustrated. A mechanism is proposed to account for the catalytic effect of ferrous salt additions, and the effect of variables on the autocatalytic nature of the reduction is described with particular reference to the dependence of the reaction rate on the available surface area of nickel metal.     

Anodic Dissolution of Copper-Zinc Alloys in Alkaline Solutions

Abstract

Potentiostatic anodic polarisation measurements on brasses (100–60 wt.-% Cu) in 0 ·150 N-NaOH are described and compared with those of the pure components. The inapplicability of current theories on anodic dissolution of homogeneous binary systems is discussed, and a possible mechanism for anodic dissolution is suggested. Dezincification of the brass surface before and during anodic polarisation is described.     

Separation and Precipitation of Nickel from Acidic Sulfate Leaching Solution of Molybdenum-Nickel Black Shale by Potassium Nickel Sulfate Hexahydrate Crystallization

Nickel was separated and precipitated with potassium nickel sulfate hexahydrate [K₂Ni(SO₄)₂·6H₂O] from acidic sulfate solution, a leach solution from molybdenum-nickel black shale. The effects of the potassium sulfate (K₂SO₄) concentration, crystallization temperature, solution pH, and crystallization time on nickel(II) recovery and iron(III) precipitation were investigated, revealing that nickel and iron were separated effectively. The optimum parameters were K₂SO₄ concentration of 200 g/L, crystallization temperature of 10°C, solution pH of 0.5, and crystallization time of 24 h. Under these conditions, 97.6% nickel(II) was recovered as K₂Ni(SO₄)₂·6H₂O crystals while only 2.0% of the total iron(III) was precipitated. After recrystallization, 98.4% pure K₂Ni(SO₄)₂·6H₂O crystals were obtained in the solids. The mother liquor was purified by hydrolysis-precipitation followed by cooling, and more than 99.0% K₂SO₄ could be crystallized. A process flowsheet was developed to separate iron(III) and nickel(II) from acidic-sulfate solution.     

Anodic Behavior of Hydrogenated Nickel in Sodium Hydroxide Solutions

The anodic behavior of hydrogenated nickel in sodium hydroxide solutions (0.01 to 1 N) is studied with the use of cyclic voltammetry, chronocoulometry, and chronoammetry. At the anodic dissolution of an -phase (Ni–0.03 at. % H), the ionization of hydrogen is limited by its diffusion in the solid phase. The diffusion coefficient of hydrogen D _H and the apparent thickness _H of the nickel layer depleted of hydrogen are calculated to be D _H = 1 × 10^–8 ± 2 × 10^–9 cm²/s and _H = 1.9 × 10^–4 cm. The D _H value is independent of the alkali concentration, while _H is independent of the duration and potential of hydrogenation. The cyclic voltammetry experiments have shown that the diffusion is unaffected by the possible formation of nickel oxides.     

Apparent Activation Energy of the Anodic Dissolution of Nickel in Sulfuric Acid Solutions in the Presence of Cl– and CNS– Ions

Apparent activation energies W of the anodic dissolution of nickel in 0.5 M H₂SO₄ are determined with the use of temperature-kinetic method at certain assumptions in a wide range of potential values E. The effect of the nature of anion-activator on the character of the W = f(E) dependence is revealed. The data obtained are interpreted in terms of the concept of hard and soft acids and bases.     

The Dissolution of a Copper Cathode in Acidic Chloride Solutions

The dissolution of cathodically polarized copper under various conditions is definitely measured. The process is most substantially affected by the concentration of dissolved oxygen, while the effect of hydrogen ions is small. Stirring the solution produces a noticeable effect at high cathodic potentials. On the surface of a copper electrode, two opposite processes proceed, namely, the ionization of copper and the deposition of copper ions. A technique for estimating the true rate of the anomalous copper dissolution when the deposition of the dissolution products is minimal is proposed. These dissolution rates of copper substantially exceed the values evaluated from the analysis of the working solution. The integral dissolution of copper is considered in terms of the chemical conjugation of the copper ionization and oxygen reduction. The hydrogen evolution is thought of as also probable.     

A Quantitative Description of the Anodic Dissolution of Nickel in Water–Organic Media1

The effect of aprotic solvent additives on the anodic behavior of nickel in aqueous sodium chloride solutions is studied. A three-parameter equation correlating the physicochemical properties of the medium (conductivity, polarity, and polarizability) with the electrochemical dissolution rate of the metal is formulated. A substantial role of conductivity agrees with the diffusion control of the processes under investigation.     

On Participation of Hydroxide Ions in the Anodic Dissolution of Metals in Aqueous Electrolyte Solutions

The increase in the anodic current at a fixed potential is formally explained by taking into account the shift of anodic partial curves with a change in pH, without invoking any concept of catalytic properties of hydroxide ions and their effect on the kinetics of any stage of the anodic process. By using the suggested thermodynamic approach, the experimental reaction orders of the anodic process in hydroxide ions are quantitatively explained.     

Dissolution of Nickel in Copper Residue Generated from Nickel Matte Refining

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Anodic Dissolution of Iron in the Solutions Simulating the Composition of Corrosive Exometabolites of Organotrophic Bacteria

Protection of Metals and Physical Chemistry of Surfaces - Abstract—Two Tafel regions with slopes of 0.06 and 0.09 V were observed on the dependences of the anodic dissolution of Fe in NaCl...     

磁场对铜在几种酸性溶液中阳极溶解的影响

研究了0～0.4T磁场对铜在中性和酸性含硫酸根溶液中阳极极化行为的影响.阳极极化曲线中的阳极电流峰和对应的电位随磁通量密度的增大而增大.增加溶液酸度会增加阳极极化曲线中电流密度-电位线性区的斜率、增大峰值电流密度,降低出现电流密度峰值的电位.外加磁场不影响中性溶液中阳极极化曲线中电流密度-电位线性区的斜率.磁场与溶液酸度对铜在高电位区的阳极溶解有协同加速作用.     

Apparent Activation Energy of the Anodic Dissolution of Nickel in Sulfuric Acid Solutions in the Presence of Cl– and CNS– Ions

Apparent activation energies W of the anodic dissolution of nickel in 0.5 M H₂SO₄ are determined with the use of temperature-kinetic method at certain assumptions in a wide range of potential values E. The effect of the nature of anion-activator on the character of the W = f(E) dependence is revealed. The data obtained are interpreted in terms of the concept of hard and soft acids and bases.     

A Quantitative Description of the Anodic Dissolution of Nickel in Water–Organic Media1

The effect of aprotic solvent additives on the anodic behavior of nickel in aqueous sodium chloride solutions is studied. A three-parameter equation correlating the physicochemical properties of the medium (conductivity, polarity, and polarizability) with the electrochemical dissolution rate of the metal is formulated. A substantial role of conductivity agrees with the diffusion control of the processes under investigation.     

Rate of Dissolution of Tin from Tinplate in Oxygen-free Citrate Solutions: I. Assessmentby polarisation measurements

Abstract

Polarisation measurements have been explored as a means of assessing the effect of coating variations and solution changes on the rate of dissolution of tin from tinplate. For comparison, dissolution rates were directly measured. Difficulties are created by the strong effects on the polarisation curves of traces of cathodically active material or of tin in solution. Corrosion currents derived from the intersection of extrapolated Tafel lines are larger than those indicated by direct measurements but provide an index for the performance of different tinplates. For this purpose and for comparison of solutions the method seems likely to be of more value as a research tool than as a basis for routine tests.     

The Rate-Determining Stage in the Anodic Dissolution of Metals

An experimental study has been made, using the potentiostat technique, of the limiting current densities of metal dissolution in electrolytic polishing solutions. The limiting current densities show the features expected for diffusion currents, and the effect of the addition of the metal dissolution product to the electrolyte indicates that it is the diffusion of this substance away from the anode which determines the overall rate of the electrode reaction. Electrolytic polishing does not occur until the limiting current density has been reached, and experiments with composite anodes show that the diffusion current densities at peaks in the surface are much higher than at cavities. These observations are interpreted by a simple diffusion layer treatment of the kinetics of the anode reaction, and their bearing upon the mechanism of electrolytic polishing is reviewed. Some practical recommendations for electrolytic polishing are made.