Sulfate Solutions Of pH Research Articles

硫酸塩浴からの変則型Fe-Ni合金電析の機構

The electrodeposition of Fe-Ni alloys was performed galvanostatically in the sulfate solutions of pH 1-3 at 40°C and the alloy deposition behavior was compared with that of Zn-iron-group metal alloys to investigate their codeposition mechanism. The deposition behavior of Fe-Ni alloy showed a typical feature of the anomalous codeposition, in which electrochemically less noble Fe deposits preferentially under most plating conditions. The anomalous codeposition behavior in Fe-Ni alloy deposition was evidently dependent on the pH buffer capacity of the solutions. This can be explained in terms of the preferential adsorption of FeOH on the deposition sites of more noble Ni due to the extremely smaller dissociation constant of FeOH+ than NiOH+ in the multi-step reduction process of hydrated iron-group metal ions.

Mechanism of Anomalous Type Electrodeposition of Fe-Ni Alloys from Sulfate Solutions

The electrodeposition of Fe-Ni alloys was performed galvanostatically in the sulfate solutions of pH 1–3 at 40 � C and the alloy deposition behavior was compared with that of Zn-iron-group metal alloys to investigate their codeposition mechanism. The deposition behavior of Fe-Ni alloy showed a typical feature of the anomalous codeposition, in which electrochemically less noble Fe deposits preferentially under most plating conditions. The anomalous codeposition behavior in Fe-Ni alloy deposition was evidently dependent on the pH buffer capacity of the solutions. This can be explained in terms of the preferential adsorption of FeOH on the deposition sites of more noble Ni due to the extremely smaller dissociation constant of FeOH þ than NiOH þ in the multi-step reduction process of hydrated iron-group metal ions.

Mechanism of the Anion Participation in Anodic Dissolution of Liquid and Polycrystalline Gallium in Acid Solutions

Unicharged anions of weak organic acids in sulfate solutions of pH 3–6 are shown to inhibit the dissolution of liquid and solid gallium in active and passive states. Dicharged anions make the dissolution of passive solid gallium rapidly accelerate and have virtually no effect on the dissolution of passive liquid gallium. Unicharged anions facilitate the oxygen atom formation on inactive surface sites. The gallium electroreflection measurements show that, regardless of the charge, weak-acid anions suppress variations in the free charge of gallium and “passivate” active dissolution without participation of oxygen.

Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

The passive state of Fe‐12% Cr and Fe‐25% Cr alloys in 1 M sulfate solutions of pH 0 and 5 was studied with a combination of electrochemical techniques: impedance spectroscopy, photoelectrochemistry, and dc resistance measurements by the contact electric resistance technique. The investigations were supported by studies on pure metal constituents (Fe, Cr) in the same solutions. As a result, the steady‐state passive film on the alloys (and on pure Cr) can be described as a thin, essentially insulating layer. Polarization of the steady‐state metal/anodic film/electrolyte system to negative and positive potentials away from the potential region corresponding to the highest electronic resistance was concluded to lead to the generation of lower or higher valency defects at the interfaces via solid‐state electrochemical reactions. These reactions result in a substantial increase of the conductivity in the first layers adjacent to either the metal/film or the film/electrolyte interface. At very negative (or very positive) potentials the film is transformed into a conductor allowing active (or transpassive) dissolution to take place. A quantitative physical model of the conduction mechanism on the basis of the surface charge approach is proposed and compared with experimental data. © 1999 The Electrochemical Society. All rights reserved.

The influence of sulfate ions on the surface enhanced raman spectra of passive films formed on iron

Surface enhanced Raman (SER) spectra were obtained from the passive films formed on iron in aqueous solutions of sulfate (pH 5 and pH 10) andborate + sulfate. The results indicate that the identities of the passive films are dependent on the pH of the solution, the identity of the anions present and the potential of iron. Either Fe(OH) 2, or a species similar to Fe(OH) 2 and which is produced by the oxidation of Fe(OH) 2, was present in all the films including those formed in the active region of the sulfate solution at pH 5. In the passive state additional species were present but could not always be unambiguously identified. The passive films formed in the sulfate solutions of pH 5 and pH 10 appeared to contain a mixture of Fe 3O 4 and γ-Fe 2O 3. In thesulfate + borate solution the passive film contained α-Fe 2O 3. The widths of the peaks in the SER spectra suggested that the constituents in the films were either microcrystalline or amorphous. In addition, in all solutions examined sulfate ions and, when present in the bulk solution, borate ions, appear to adsorb on the surface of the passive films. In the case of the films formed in the sulfate solution of pH 5, sulfate ions were covalently bonded in the films in a bidentate configuration.

Influence de l'oxygene et des ions chlorure sur le comportement electrochimique d'un alliage FeNi (36 % Ni) en milieu acide et neutre

An investigation of the behaviour of a FeNi alloy (64-36) was undertaken in sulfate solutions of pH from 1.7 to 9, and the effects of Cl − ions and dissolved oxygen were examined. In the absence of these two species, the alloy is in the active state in the whole pH range and only becomes passive in neutral solutions at high concentrations of oxygen. Pitting was found to occur only in acidic solutions in the presence of Cl − ions.

ChemInform Abstract: HYDROGEN EVOLUTION REACTION ON SMOOTH TUNGSTEN CARBIDE ELECTRODES

AbstractDas H‐Potential an einer rotierenden WC‐Elektrode (wobei sowohl nicht aktivierte als auch aktivierte Proben verwendet werden) in H2 gesättigten 0.5 M SOF‐Lösungen (pH 0.3 und 1.85′) wird im Temperaturbereich 30‐80°C untersucht.

Hydrogen evolution reaction on smooth tungsten carbide electrodes

The open-circuit potential in H 2-saturated electrolytes, and the kinetics of hydrogen reactions, in particular of hydrogen evolution reaction, on smooth, rotating disc tungsten carbide WC electrode have been investigated, in 0.5 M sulfate solutions of pH 0.3 and 1.85, in the temperature range 30 to 80°C. Anodically activated electrodes were used too. It was proved that values of the open-circuit potential in the near vicinity of reversible hydrogen electrode potential can be observed, under condition of high purity, and of tight mounting of the sample in the electrode holder. Two Tafel regions have been observed for hydrogen evolution reaction, both the Tafel slopes having no systematic variation with temperature. In the lower overpotential region the experimental charge transfer coefficient attained the value of 1, when the temperature was increased up to 80°C. It was suggested that the process approached the barrierless form when the temperature was increased. The mechanism of hydrogen reactions on WC was discussed. It was suggested that the rate of the process is possibly determined by the rates of its two steps simultaneously. The role of pH on the activation process of WC was emphasized, and implications of the hydrogen evolution reaction parameters on the mechanism of this process were pointed out.

The Thermodynamics and Electrode Kinetic Behavior of Nickel in Acid Solution in the Temperature Range 25° to 300°C

The electrode kinetic behavior of nickel was studied by potentiokinetic, potentiostatic, and potential decay techniques in sulfate solutions of pH 1.3, 3.4, and 6.3 adjusted to constant 0.1N ionic strength by additions. The active‐passive transition characteristic of the room temperature behavior of nickel was found to be absent at temperatures above 100°C. However, at temperatures above 250°C, indications of oxide formation were found although there was little contribution to passivity therefrom. In addition, the temperature stability of passive films and these oxides seems to be pH dependent. Theoretical potential‐pH diagrams were also constructed for the nickel‐water systems for the temperature range used in these experiments.

Surface Studies on Passive Iron

Surfaces of zone‐refined iron in sulfate solutions of pH between 1 and 15 have been studied by measurement of electrode capacity and by chronopotentiometry. Capacities were measured as a function of potentiostatically controlled average electrode potential by a recently developed pulse technique. The capacity curves thus obtained were approximately plateaus over potential regions in which oxygen or hydrogen evolution occurred at >10 µa cm−2. In intermediate potential regions the curves had shallow minima as low as 4 µfarad cm−2 near the potential region of oxygen evolution and peaks with maxima as great as 165 µfarad cm−2 near the potential region of hydrogen evolution. The capacity values depended on the history of the potential variations applied to the electrodes. Chronopotentiometry indicated the presence of at least two sorts of reducible surface material under most of the experimental conditions. Results are interpreted to indicate the presence of a surface material with properties which depend on the electrode potential and solution environment during its formation and which are significantly different from those of any known crystalline, stoichiometric iron oxide. Such properties of the material of a passive iron surface may be reasonably explained by a previously presented hypothesis of a surface material formation sequence initiated by the adsorption of solution species.

An ion-exchange method for the separation of thorium from rare earths, and its application to monazite analysis

Thorium is adsorbed on a strongly basic akionexchange resin, Amberlite IRA-400 (sulfate form), from a sulfate solution of pH about 2.0. Under these conditions, tervalent cerium and other rare earths are adsorbed to only a slight extent. An ion-exchange method has been developed for the separation of thorium from these elements. The method has also been applied to the determination of thorium and rare earths in monazite concentrates. (auth)