Theory of generalized variables in electrochemical kinetics: Simulation of the slow discharge theory equations

It is shown that theory of similarity and analysis of dimensionalities (theory of generalized variables) is applicable for a kinetic analysis of a simple electrochemical reaction described by equations of the slow discharge theory. The corresponding dimensionless complexes are derived and quantitative interrelation between them is analyzed.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 116–120.Original Russian Text Copyright © 2005 by Protsenko, Danilov.     

Evaluation of reinforcement corrosion rate in concrete structures by electrochemical noise measurements

Experimental results on the polarization resistance estimation in a three-electrode setup that consists of two carbon steel electrodes and the silver reference electrode are presented. The corrosion rate varies with the conditions changing inside the concrete structure due to its irregular wetting in an aqueous solution of NaCl. The change of polarization resistance of a single steel electrode can be identified by voltage and current electrochemical noise measurements. The observed change does not exceed the factor of a few times of the originally recognized value. The newly proposed method of electrochemical noise analysis for monitoring of swift corrosion rate changes is presented in detail. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 611–616. The text was submitted by the authors in English.     

Sources of electrochemical noise in corroding systems

The electrochemical noise method is reasonably well established as a technique that can estimate corrosion rate through the electrochemical noise resistance or impedance. A more interesting potential application is the identification of the nature of the corrosion process. In this paper, a number of corrosion types are examined, and it is concluded that the majority constitute a form of shot noise, possibly with a superimposed baseline current. Methods by which parameters describing the shot noise process can be estimated from the measured data are presented. It appears to be feasible to extract the charge in the shot noise events, and their frequency, providing all of the anodic or cathodic current, is associated with these events. However, the analysis requires a number of assumptions that are not always valid, and these are discussed. Finally, some alternative methods that have been used to identify the type of corrosion are briefly discussed. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 557–566. The text was submitted by the author in English.     

Polymer matrix of polyethylene porous films functionalized by electrical discharge plasma

The polyethylene porous films were treated by dielectric surface barrier discharge (DSBD) plasma at atmospheric pressure in oxygen (O₂) or nitrogen (N₂), and by radio-frequency discharge (RFD) plasma in air at reduced pressure 46 Pa. The surface energy of films was carried out by direct measurements of contact angles of six testing liquids. The strength of adhesive joints in the system modified polyethylene porous films - polyacrylate was measured by peeling of the joints under the angle of 90°. The significant increase of the surface energy and its polar component of polyethylene porous films modified by all types of plasma were observed. The higher strengths of adhesive joints were found for modification of polyethylene porous films by radio-frequency discharge plasma in comparison with modification of the films by barrier discharge plasma.     

Theory of the shot noise in electrochemical bridge contacts

Correlation functions of the current and the noise power for a redox-group-containing electrochemical tunnel contact are calculated under the assumption on a shot character of the electron tunneling. Weak and strong interaction between the redox group and electrodes is considered. Overvoltage dependence of the Fano factor at different bias-potentials is found. The conditions of passing of the calculated dependences into the Schottky law are formulated.     

Dynamics of lithium electrode passivation in aprotic organic electrolytes,studied by electrochemical noise method

Lithium electrode passivation is studied in different organic electrolytes, namely, 1 M LiClO₄ in 1,3-dioxolane, 1 M LiN(CF₃SO₂)₂ in 1,3-dioxolane, 1 M LiPF₆ in an ethylene carbonate-diethyl carbonate mixture, 1 M LiPF₆ in an ethylene carbonate-dimethyl carbonate mixture, using the electrochemical noise method. The dynamics of passive film formation on the lithium surface in the mentioned electrolytes that differ in their corrosivity towards lithium is followed.     

Electrochemical noise generated during the stress corrosion cracking of sensitized alloy 690

Electrochemical noise in current has been used to monitor the stress corrosion cracking (SCC) susceptibility of alloy 690 sensitized at 700 °C during 48 h in sodium thiosulfate at 90 °C. At 48 h of aging, the specimen failed by SCC and the corrosion current pulses had high intensity and low frequency, and were associated with the nucleation and propagation of stress corrosion cracks during slow strain rate tests. When the alloy was immune to SCC, the observed corrosion current pulses had a much higher frequency and lower intensity, indicating either uniform corrosion or passivation. The type of transients observed do not indicate the mechanism responsible for the observed embrittlement, but only the cracking initiation or propagation process.     

Sub-millivolt amplitude potential oscillations observed in the noise of hydrogen evolution on Ag and Cu microelectrodes

A strange effect was observed while using the method of quasi-simultaneous determination of electrochemical voltage noise and impedance to obtain information on the kinetics of the hydrogen evolution reaction on Ag and Cu microelectrodes. Beyond a certain polarizing current density we found microvolt-amplitude potential oscillations on both electrodes with a frequency in the 5 Hz–5 kHz range. The oscillations were observed in every single experiment with Ag and Cu, while no oscillatory behavior was observed during the control experiments with the Pt microelectrode. The presence of the oscillations indicates that the mechanism of hydrogen evolution is more complex compared to the original assumption.      

Decomposition of an organophosphorus material in a silent electrical discharge

An organophosphorus compound, C₇H₁₆FO₂P, was reacted with air in a silent ac discharge. This paper discusses the observed fragmentation and products of the reaction using Gas Chromatography-Mass Spectrometry.     

Experimental correlation between metallographic evaluation and electrochemical noise in intergranular corrosion tests of aluminium alloys

In the present work, the correlation between the metallographic evaluation and electrochemical noise (EN) in intergranular corrosion (IGC) tests of aluminium alloy 2024‐T3 has been analysed. For this purpose, the influence of temperature and hydrogen peroxide concentration on the IGC attack has been studied. Similar IGC was observed between 20 and 40 °C, showing a low dependence with temperature (at least in this range). Hydrogen peroxide was seen to have a strong effect, leading to IGC activation when raising its concentration. The results of the detailed metallographic evaluation of the samples after the tests were analysed together with the EN measured during the tests. The averaged noise resistance was inversely proportional to the depths of the attacks, whereas the average of the parameter so‐called ‘Statistical Noise Power’ was directly related to the IGC degree. The metallographic evaluation and the EN showed a reasonable experimental correlation. Copyright © 2012 John Wiley & Sons, Ltd.     

On the fluctuation representation of the slow discharge equation

By using the Crookes’ fluctuation expressions, general fluctuation representation of antisymmetric part of the current-voltage characteristic of slow discharge is obtained. The obtained result is compared with the slow discharge current-voltage characteristic corresponding to the Bochkov-Kuzovlev-Jarzynski’s fluctuation expression. It is demonstrated that in terms of the Bochkov-Kuzovlev-Jarzynski-Crookes theory there exist two quite dissimilar versions of the fluctuation representation of antisymmetric part of the current-voltage characteristic of slow discharge. The contradictory character of the Bochkov-Kuzovlev-Jarzynski-Crookes theory points to topicality of further development of the elementary act fluctuation theory.     

Electrochemical noise of a lithium electrode in organic electrolytes: A study by a correlation function method

Fluctuations of the potential of a lithium electrode in conditions of galvanostatic polarization in aprotic organic electrolytes are studied by a method of correlation functions. Computer-aided removal of heavy interference in the form of slow variation of the electrode potential proved to be possible to perform with use made of fifth-power polynomials. The time coordinate of the first zero in the correlation function weakly depends on the electrolyte type and lies within the limits 1.5–3 s. At the same time, the electrolyte type affects the dispersion of the electrode potential fluctuations in a substantial manner. In so doing, lithium systems that feature a high cycling efficiency possess a lower level of noise.     

Tuning of electron transport through molecular bridge systems: A study of shot noise

We study electron transport characteristics through a single phenalenyl molecule attached with two nonsuperconducting electrodes by the use of Green's function technique. Parametric calculations are given based on the tight‐binding model to characterize the electron transport through such molecular bridge system. It is observed that the electron transport properties are significantly influenced by (a) the interference effect and (b) the molecule‐to‐electrodes coupling strength. In this context we also describe the noise power of the current fluctuations that provides an important information about the electron correlation, which is obtained by calculating the Fano factor (F). The knowledge of this current fluctuations gives a key idea for fabrication of efficient molecular devices. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Contribution to electrical discharge electron beam system for flue gas cleaning method

Many authors have investigated simultaneous reduction of SO₂ and NO_x from flue gas stack emission by electron beam-induced plasma process. Because of high costs, this technology has been applied in only a few countries (Japan, China and Poland) until now. Small countries, consumers of cheap combustibles, produce a great deal of atmospheric pollutants SO₂ and NO_x, For this reason there is a great interest in the implementation of cheaper technologies with a similar impact as electron beam processing. This paper presents a series of experimental data for SO₂ and NO_x removal by electron beams, electric discharge and ozone in different processing variants of flue gas.     

On plasma composition of a pulsed discharge in electrolyte

The equilibrium plasma composition for a system containing H, O, N, Na, and Cu is determined for the temperature range between 5000–20,000 K. This corresponds to the pulsed discharge plasma in electrolyte with energy dissipation which is near threshold. For computing the plasma composition of the system based on the minimization of free energy, the method of steepest descent was used. The plasma composition was calculated for different electrolyte contents, conductivity, and various external pressures.     

Photocatalytic activity of ZrO2 nanoparticles prepared by electrical arc discharge method in water

ZrO₂ nanoparticles were synthesized through arc discharge of zirconium electrodes in deionized (DI) water. X-ray diffraction (XRD) analysis of the as prepared nanoparticles indicates formation a mixture of nanocrystalline ZrO₂ monoclinic and tetragonal phase structures. Transmission electron microscopy (TEM) images illustrate spherical ZrO₂ nanoparticles with 7–30 nm diameter range, which were formed during the discharge process with 10 A arc current. The average particle size was found to increase with the increasing arc current. X-ray photoelectron spectroscopy (XPS) analysis confirms formation of ZrO₂ at the surface of the nanoparticles. Surface area of the sample prepared at 10 A arc current, measured by BET analysis, was 44 m²/g. Photodegradation of Rhodamine B (Rh. B) shows that the prepared samples at lower currents have a higher photocatalytic activity due to larger surface area and smaller particle size.     

Confirmed assignments of isomeric dimethylbenzyl radicals generated by corona discharge

The controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By employing corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of 1,2,4-trimethylbenzene. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion, we revised previous assignments of the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. Spectroscopic data of electronic transition and vibrational mode frequencies in the ground electronic state of each isomer were accurately determined by comparing them with those obtained by an ab initio calculation and with the known vibrational data of 1,2,4-trimethylbenzene.     

The efficacy of heating low-pressure H2 in a microwave discharge

The relative ease with which a low-pressure hydrogen stream may be heated in an electrical discharge suggests that such a system be considered in current efforts to develop thrusters for spacecraft orbit raising purposes. In this work a detailed model of a microwave discharge in flowing, low-pressure hydrogen is used to interpret and clarify experimental measurements of atom concentration, electron energy, and electron density. The radially averaged, constant-pressure model accurately reproduces the experimental data and also calculated the rates of a number of gas-heating and wall-heating processes as well as rates of energy deposition into coolant and working fluid streams. The calculated gas-heating rates indicate that the gas heating is due primarily to the thermalization of the energetic atoms produced by dissociation of H₂ via excitation of theb ³∑ _u ⁺ state. The calculations also indicate that the energy flux to the quartz tube is significantly influenced by Lyman and Werner band radiation and by heterogeneous atomic recombination processes and, to a much lesser degree, by electron-ion recombination processes. The fraction of power input which is ultimately transferred to the gas stream is a decreasing function of the power input and varies from 0.24 to 0.12.     

滑动弧放电等离子体分解甲醇制氢

对常温常压下滑动弧放电等离子体直接分解甲醇进行了研究,探讨了载气流量、甲醇浓度、电极间距、输入电压和气化室温度等实验参数的影响。结果表明,不同操作条件导致甲醇转化率由51%升高到81.7%,氢气和一氧化碳的选择性之比基本保持一个固定值。除了氢气和一氧化碳,产物中还检测到了少量的甲烷和C₂不饱和烃以及痕量二氧化碳。不同于传统的甲醇热分解机理,提出了滑动弧放电等离子体甲醇分解的制氢路径。     

Steel surface processing by a continuous optical discharge plasma

The influence of a continuous optical discharge (COD) plasma generated in flowing argon and argon-nitrogen mixture on alloy and carbon steel surfaces has been investigated. Changes in the structure, element composition, and microhardness of steel surface layers under the action of a COD plasma and laser beam were observed. In the presence of a COD plasma the microhardness distribution in hardened zone reaches its maximum at the metal surface and is different from that measured for samples processed by laser beam only.