Dependence Of Current Efficiency Research Articles

ПРЕДЕЛЬНО-КВАЗИСТАЦИОНАРНАЯ МОДЕЛЬ ЭЛЕКТРОХИМИЧЕСКОГО ФОРМООБРАЗОВАНИЯ

The paper is focused on modeling of electrochemical machining in quasistationary approximation. The modeling is based on the use of Faraday’s and Ohm’s laws. The dependence of current efficiency on the current density in the form of a step function is used when solving this problem. The model enables us to study the configuration of a machining area, obtained in case of extreme high localization of a solution process. For this function there is a possibility in case of a non-steady process to divide sections of the machining area into zones with different conditions (presence and lack of solution). As the solution in case of such machining happens at a constant value of intensity module, there is a possibility to simulate the change of machining time by embedding of an electrochemical machining electrode into the edge of a workpiece. The evidence from practice shows that the accuracy of approximation of the non-steady process by quasistationary has three and more significant digits. Meanwhile, the computing time decreases by 100 and more times. The problem of shaping while machining by the machining electrode in the shape of a plate with the isolated top surface is solved. The methods of the complex variable theory have been used to solve the problems on the assumption about constancy of electrolytic conduction. The Joukowski and Schwarz-Christoffel transformations are applied to construct conformal mapping. The accurate solution on the problem in quadratures is obtained. The study on non-steady processes using a quasistationary model makes it possible to get information about a shape of the machining area at the beginning, continuation and the end of the machining process. In particular, it’s found out that near the section of the machining start there is a solution like outflow from the board, well-known in hydrodynamics. It allows examining properties of a shape that is formed at the edge of the machining area.

Effect of Current Efficiency on Electrochemical Micromachining by Moving Electrode

In this work, the effect of current efficiency on the electrochemical micromachining by moving electrode is studied theoretically. The Laplace equation for the electric potential and the equation of workpiece surface evolution are used as the mathematical model of the process. A new scheme of solution of free boundary problem for steady-state electrochemical micromachining is proposed. According to the scheme, the initial approximation of the workpiece surface is prescribed. In the course of modeling, the workpiece surface moves in the normal direction at a rate proportional to the discrepancy of the steady-state condition. The effect of various dependences of current efficiency on the local current density is analyzed. As a result of simulation, the dependences of the shape and sizes of machined surface on the current efficiency and the machining parameters are obtained.

Indirect Electrochemical Reduction of Indigo on Carbon Felt: Process Optimization and Reaction Mechanism

A carbon felt was used as the cathode material for the indirect electrochemical reduction of indigo in alkaline aqueous solution employing iron-triethanolamine (Fe-TEA) complex as a redox mediator. Surface structure and specific surface area of the carbon felt electrode and its electrochemical performance toward the reduction of indigo were investigated by SEM, BET, and cyclic voltammetry, respectively. Moreover, an optimization of different operating conditions for the reduction of indigo was performed with an H-cell. In particular, the dependence of current efficiency (CE) on electrolysis time was chosen to analyze the indirect electrochemical reduction mechanism of indigo. The results showed that the carbon felt, having a high specific surface area of approximately 7289 cm2·g–1, is an excellent electrode material for the indirect electrochemical reduction of indigo and that a moderate current density, temperature, and concentration of indigo has the most beneficial effects on the reduction process.

Electrodeposition of nanocrystalline chromium-carbon alloys from electrolyte based on trivalent chromium sulfate using pulsed current

The effect of the parameters of pulsed electrolysis on the current efficiency, nanocrystal size, composition, hardness, friction coefficient, and wear resistance of nanocrystalline Cr-C coatings obtained from electrolyte based on Cr(III) sulfate containing carbamide and formic acid is studied. It is shown that coatings contain ∼9 wt % of carbon; the current density and pulse ratio produce practically no effect on their composition. It is found that a maximum appears on the dependence of current efficiency on pulse ratio in the case of the pulse ratio of ∼1.05–1.1. Thereby, current efficiency greatly exceeds the value implemented in the steady-state current mode. It is shown that, if the microhardness of Cr-C deposits obtained at constant current is close to 850–900 HV, the microhardness may increase to ∼1200−300 HV when pulsed electrolysis is used in certain modes. It is found that application of pulsed electrolysis allows a significant decrease in the friction coefficient of chromium-carbon coating (steel counterbody) both under the dry friction conditions and in the case of boundary lubrication and also results in an increase in the deposit wear resistance.

Numerical simulation of the electrodeionization (EDI) process accounting for water dissociation

The electrodeionization process (EDI) is usually operated at overlimiting current density, and is thus characterized by water dissociation and concentration polarization. We attempt to study the useful and harmful effects of water dissociation on the EDI process. A numerical steady state model was established to simulate the process of EDI, accounting for the effects of water dissociation. The differences in concentration polarization of membranes were investigated to study the effects of water dissociation on cation and anion membranes. Protons produced by water dissociation caused the resin to transform into the H-form. The H-form resin, which has high conductivity and high transport number, depletes protons in the interstitial solution. This explains the experimentally detected phenomenon that at high current densities, the pH value of the effluency of the dilute compartment (DC) stops decreasing when current increases. We suggest that the useful role of water dissociation in EDI is due to the H-form resin bringing more salt cations of the interstitial solution into the resin phase, thus producing a high conductivity channel for the electro-migration of the salt cations. This mechanism avoids the decrease in salt ion conductivity brought about by concentration polarization. The disadvantageous effect of concentration polarization on the transportation of salt ions in interstitial solution is thus lessened. An intermediate point between the useful and harmful effects of water dissociation was determined by the dependence of current efficiency and removal rate for both cations and anions as a function of current density.

Kinetics of electrodeposition of Ni-Sn alloy deposits from an acid chloride bath

Total and partial polarization curves were determined for the deposition of tin and nickel separately as well as for their codeposition from acidic chloride baths. Using a rotating disc electrode system a detailed study of Ni2+, Sn2+ and H+ reduction processes was made, and the results were compared with similar studies on the deposition of such alloys from the same electrolyte with fluoride addition. It was found that for chloride baths the alloy is deposited with a higher polarization than that for the deposition of each metal separately, which is the reverse of the case of deposition from electrolytes containing fluoride ion additions. Furthermore, for coreduction there is a decrease in the hydrogen discharge overvoltage; the rate of hydrogen reduction considerably exceeds the discharge rate of other alloy components, and the hydrogen reduction reaction is diffusion controlled. The tin reduction reaction (for both separate deposition and codeposition) was found to be diffusion controlled, while for nickel reduction in both cases the reaction kinetics are mixed with the activation kinetics dominant. The dependences of current efficiency and of percentage content of tin in the alloy on current density were also investigated. The investigations showed that, although there exists a considerable difference in the electrocrystallization process of Ni-Sn plate from chloride baths and from baths with F- additions, it is possible to choose electrolysis conditions which will allow plates with good properties to be obtained from the bath which contains chloride only.

Electrodialysis using ion‐exchange membranes. I. Factors limiting the degree of desalting

AbstractThe behaviour of potassium chloride solutions in a continuously operated electrodialysis cell using ion‐exchange membranes is described. The cell contained 25 desalting compartments and 25 concentrating compartments each 1.58 mm. thick. The membranes were supported by perforated separators carrying grooves for the passage of liquid, and turbulent flow was induced by forced recirculation. The dependence of current efficiency on the ion concentration in the desalting compartments was assessed and the effect of a number of design factors was investigated. Theoretical expressions have been derived for the current efficiency of the desalting process.