A. D. Davydov

Natural-convective instability of electrochemical systems: A review

Basic theoretical and experimental results of research into natural-convective instability of electrochemical systems are considered.

Breakdown of valve metal passivity induced by aggressive anions

As an example of the anodic behavior of niobium in bromide solutions, an effect of the following factors on the process of breakdown of valve metal passivity is shown: the adsorption of aggressive anions and their incorporation into the anodic oxide film; the solution composition including the concentration of aggressive ions and the presence of foreign substances; the solvent essence; and defects of the oxide film. A physical model of the breakdown process is also proposed.

Measurements of platinum electrode potential in blood and blood plasma and serum

The method of electrochemical pretreatment of platinum electrode with the goal of standardizing the initial state of electrode surface and its open-circuit potential (OCP) in the blood and other biological media is proposed. The platinum electrode potential is measured in 0.14 M Na2SO4 aqueous solution, in the blood and blood plasma and serum. By the examples of OCP measured in the blood serum of patients with acute poisoning, acute cerebral pathology and patients treated by the method of hyperbaric oxygenation, it was found that the values of blood serum OCP were different for studied pathological states and healthy people.

Simulation of ion transfer under conditions of natural convection by the finite difference method

Abstract The finite difference method of calculation of non-steady-state ion transfer in electrochemical systems under the conditions of natural convection is elaborated. The method is based on the mathematical model involving the continuity equations for electrolyte species, the condition of electroneutrality, and the Navier–Stokes equations for a viscous incompressible liquid with the corresponding initial and boundary conditions. A scheme of decoupling is proposed, which provides successive calculation of the field of hydrodynamic velocities (a stream function), the distribution of electric potential, and the distribution of electrolyte species concentrations subject to the condition of electroneutrality. To enhance the efficiency of the method at large Schmidt numbers, the distribution of electrolyte species concentrations was calculated by the implicit difference scheme. The results of computational experiments are reported.

Electrochemical noise diagnostics: Analysis of algorithm of orthogonal expansions

The algorithm of orthogonal expansions is applied to the problem of extraction of diagnostic information from random noise. It is shown that the spectral analysis of electrochemical noise can be performed by a unified algorithm regardless of the type of orthogonal expansion used. A multi-channel indicator of color of electrochemical noise can be constructed on the basis of the orthogonal expansions. It is concluded that the algorithm of orthogonal expansions is an advantageous tool for noise monitoring and noise diagnostics of practically important electrochemical devices, including the devices of electrochemical energetics and systems of protection against corrosion.

Development of pitting corrosion of stainless steel 403 in sodium chloride solutions

Pitting corrosion of stainless steel 403 in the NaCl solutions is studied. It is shown that the experimental results obtained under the potentiostatic conditions do not provide sufficient information on the behavior of steel under the conditions of free corrosion. The corrosion experiments take long time, their results exhibit poor reproducibility; however, they are necessary for obtaining reliable data on the corrosion behavior of steel. The development of corrosion process is reflected in the variation of corrosion potential with time. The effect of concentration and temperature of NaCl solutions on the development of pitting corrosion is studied. The peculiarities of the distribution of pits over the test specimen surface are revealed. In 1 M NaCl solution at 20°C, few pits arise. Some of them repassivate; some pits grow, initially, in diameter and depth and, then, almost only in depth. The examples of through pit formation on the specimens 4 mm thick are presented.

Finite difference method of simulation of non-steady-state ion transfer in electrochemical systems with allowance for migration

Finite difference methods of the second order of accuracy are elaborated for numerical calculation of non-steady-state ion transfer, which is caused by diffusion, migration, and convection in the unidimensional electrochemical systems. The methods of decoupling a set of coupled continuity equations of the electrolyte species are proposed, which ensures that the discrete equations are consistent with the initial differential equations and the electroneutrality condition is rigorously met. The methods of approximation of the boundary conditions of the second order temporal and spatial accuracy and the method of decoupling the transfer equations in the boundary nodes are elaborated. The explicit, fully implicit, and semi-implicit finite difference schemes are elaborated. For semi-implicit schemes, two versions of difference equation closure are proposed, which assure the unambiguity of determination of the distribution of electrical potential. Comparison analysis of the accuracy of elaborated finite difference methods of calculation of non-steady-state ion transfer is performed.

Theoretical study of the effect of electrochemical cell inclination on the limiting diffusion current

The effect of inclination of electrochemical cell with plane-parallel electrodes in the gravitational field on the limiting current of electrochemical reaction is theoretically analyzed by the example of iodine � /iodide system. The quantitative dependences of the limiting current on the angle a between the electrodes and the horizontal are obtained. It is shown that this effect is associated with the variation in the distributions of solution concentration and hydrodynamic velocity with a . It is found that the ratio between the electrode’s length and the interelectrode distance is of great importance. # 2002 Elsevier Science Ltd. All rights reserved.

Numerical Modeling of Non-Steady-State Ion Transfer in Electrochemical Systems with Allowance for Migration

Numerical methods that are used for modeling non-steady-state ion transfer in electrochemical systems and account for the diffusion, migration, convection, and homogeneous chemical reactions are analyzed. It is shown that the violation of the electroneutrality condition (ENC) in the process of numerical solution is due to the difference equations being inconsistent with the initial differential equations. Difference schemes for numerical calculation of transfer processes, which make it possible to split a set of coupled equations, are designed and conditions for their stability are determined. The explicit difference scheme is self-consistent, i.e. it ensures that ENC is rigorously met. In the implicit difference scheme, ENC is probably violated when splitting the set of equations. To restore electroneutrality of the medium, it is proposed to use a physically substantiated analytical relation for the space charge relaxation under the action of a strong electric field.

Template electrodeposition of metals. Review

The works devoted to the electrodeposition of metals, alloys, and semiconductors onto the substrates through the templates of various non-conducting materials with pores of various shapes and sizes are reviewed. The composite materials, nanowires, metal foams, and the parts with nanostructured surface obtained by this method are promising materials for the electrocatalysis, electroanalysis of media, development of various sensors, modern miniature magnetic memory devices, optoelectronics, power sources, etc.