摘要： The kinetics of electrochemical processes under the conditions of a slow chemical reaction in solution is analyzed in a general form, which admits a change in their limiting stages. The main feature of polarization curves for the electrochemical processes is the existence of two Tafel portions with slopes corresponding to a slow homogeneous chemical reaction (lower portion) and a preceding faster electrochemical stage (upper portion with a higher slope).

关键词： liquid vertical bar liquid interfaces   Gibbs energy of transfer   graphite electrode   ion transfer  

摘要： Droplets of polar and nonpolar aprotic solvents containing dissolved electroactive species can be easily attached to paraffin-impregnated graphite electrodes. When the electrode with the attached droplet is introduced into an aqueous electrolyte solution, the electrochemical reactions of the dissolved species can be elegantly studied. Provided thr droplet does not contain a dissolved electrolyte, the electrochemical reaction will be confined to the very edge of the three-phase junction droplet I graphite I aqueous electrolyte. When a neutral species is oxidised, two pathways are possible: the oxidised species can remain in the droplet and anions will be transferred from the aqueous solution to the organic solvent, or the oxidised species may leave the droplet and enter the aqueous solution. Depending on the nature of the dissolved species, the nature of the organic solvent, the presence or absence of appropriate anions and cations in the two Liquid phases, very different reaction pathways are possible. The new approach allows studies of ion transfer between immiscible solvents to be performed with a three-electrode potentiostat. Electrochemical determinations of the Gibbs energy of ion transfer between aqueous and nonpolar nonaqueous liquids are possible, whereas conventional ion transfer studies require the presence of a dissociated electrolyte in the organic phase. The new method considerably widens the spectrum of accessible ions. (C) 2000 Elsevier Science S.A. All rights reserved.

关键词： electrochemical membrane process   simultaneous recovery   copper   citrate   NTA   EDTA  

摘要： An electrochemical membrane process was used to treat complexed Cu-II solutions of citric acid, nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA). An equimolar solution of Cu-II and complexing agent was focused. The iridium oxide (IrO2/Ti) and Pt (Pt/Ti) coated on titanium were used as anode and cathode, respectively. The cation exchange membrane Neosepta CM-1 was adopted. Experiments were carried out at different current densities (18.5-139 A/m(2)), initial catholyte pH and Cu-II concentrations (0.01-0.08 M), and initial anolyte NaNO3 concentrations (0.001-0.2 M). An economically feasible current efficiency and recovery percentages of metals and complexing agents could be achieved if the concentration of the complexed Cu-II was sufficiently high. (C) 1999 Elsevier Science Ltd. All rights reserved.

关键词： new developments   electrochemical etching (ECE)   polycarbonate (PC) detectors   chambers   ECE procedures   photoneutrons   ethylene diamine   background reduction   alpha spectrometry   image processing  

摘要： Some highlights of new developments made in our laboratory at the Atomic Energy Organization of Iran on chemical and electrochemical etching (ECE) of polymer track detectors like polycarbonate (PC) are presented. They include introduction of new ECE chamber systems and methods for production of ECE signs and symbols, and a new versatile ECE chamber (VECE) system for multi-purpose, multi-size, and/or multi-shape detector processing;determination of photoneutron doses in and around high-energy X-ray beams of a 20 MV medical accelerator;verification of the Smythe and Mason equations for ECE of tracks in polymers;ECE of alpha and recoil tracks in PC using PMW, PEW and PEMW etchants;introduction of a novel method using ethylene diamine for treatment of PC detectors with its applications, for example in precision removal of surface layers of PC (e.g, bulk removal rates of about 0.04, 0.15, 0.36, 0.66, and 1.33 mm min(-1) for 60%, 65%, 70%, 75% and 80% ethylene diamine solution (v/v) in water respectively, with no effects on its transparency), and in significant reduction of background track density of PC detectors, in alpha energy discrimination and alpha spectrometry;and development of an image processing system for track counting and measurements;etc. Some main results are reviewed and discussed.

关键词： 电气化建设   整体推进   吉水县   农村初级电气化建设   橡胶坝   机组安装   电网建设   小水电上网   水电局   中心变电站  

关键词： 铁路电气化   事业   铁路现代化   电气化铁道   电力机车   电动机车  

摘要： 铁道部部长傅志寰在全路广大干部职工高举邓小平理论伟大旗帜，认真贯彻党的十五大精神，掀起跨世纪铁路建设新高潮之际，我们迎来了我国第一台电力机车诞生４０周年。这４０年是我国电气化铁路迅速发展，各项技术装备水平全面提高的４０年，也是我国电力机车工业从无到有...

关键词： voltammetry   interface   platinum   oxygen ion conductor   oxygen electrode   gas phase  

摘要： Electrochemical processes occurring at the interface Pt/BICUVOX.10 were investigated by cyclic voltammetry and potentiostatic current-potential curves, taken under steady-state conditions, in different mixtures of nitrogen and oxygen at temperatures between 300 and 600 degrees C. Similar experiments were carried out for comparison at the Pt/YSZ interface. Point or paste electrodes were used. The equilibrium of the oxygen electrode is not established below 500 degrees C at both interfaces any more. Reasons for this behavior are presented. It is concluded on the basis of a comparison of the shape of voltammograms at different interfaces that BICUVOX.10 is reduced and oxidised electrochemically. Simultaneously a reoxidation of the solid elctrolyte by O-2 from the gas phase occurs. At temperatures below 500 degrees C the reoxidation is not fast enough to avoid a hysteresis at cathodic currents of the voltammograms. At higher temperatures and larger partial pressures of O-2 the hysteresis disappears. (C) 1997 Elsevier Science Ltd.

关键词： interface   ionic conductivity   stabilized zirconia   cyclic voltammetry  

摘要： Electrochemical processes occurring at the interface platinum\yttria-stabilized zirconia were investigated by cyclic voltammetry and potentiostatic current-potential curves, taken under steady-state conditions, in different mixtures of oxygen and nitrogen at temperatures between 300 and 600 degrees C. Point or paste electrodes were used. The exchange current of the rate-determining step of the oxygen reduction becomes very small below 500 degrees C. Therefore, the equilibrium of the oxygen electrode is no longer established. A layer of chemisorbed oxygen atoms is formed anodically on the contact surface of the point electrode, not by the dissociation of O-2 at the three-phase boundary. The shape of the cyclic voltammograms is discussed. (C) 1997 Elsevier Science S.A.

关键词： electrolytes   photoluminescence   electrochemical electrodes   anodised layers   semiconductor device testing  

摘要： Photoluminescence (PL) with short N-2-laser pulses is a plied for in situ monitoring of electrochemical processes at the (100) p-Si/aqueous NH4F electrolyte interface during anodic oxidation followed by electrochemical hydrogenation at low cathodic potential. The anodic oxidation is carried out in a potential regime where electropolishing with current oscillations occurs. The etch rate of the anodic oxide, which is characterized by the reciprocal oscillation period(10) is changed by the composition of the fluoride solution. At the minimum of the current oscillations the PL intensity increases with decreasing etch rate and anticorrelates with the oxidation rate, which is monitored by the current. The hydrogenation of the Si surface is characterized by the anodic current transient. The PL intensity increases strongly during the decay of this transient.

关键词： luminescence   photochemistry   redox chemistry   self-assembly   self-complexation   template syntheses  

摘要： Photochemical control of a self-assembled supramolecular 1:1 pseudorotaxane (formed between a tetracationic cyclophane, namely the tetrachloride salt of cyclobis(paraquat-p-phenylene), and 1,5-bis[2-(2-(2-hydroxy)ethoxy)ethoxy]naphthalene) has been achieved in aqueous solution, The photochemical one-electron reduction of the cyclophane to the radical trication weakens the noncovalent bonding interactions between the cyclophane and the naphthalene guest-pi-pi interactions between the pi-electron-rich and pi-electron-poor aromatic systems, and hydrogen-bonding interactions between the acidic alpha-bipyridinium hydrogen atoms of the cyclophane and the polyether oxygen atoms of the naphthalene derivative-sufficiently to allow the guest to dethread from the cavity;the process can be monitored by the appearance of naphthalene fluorescence. The radical tricationic cyclophane can be oxidized back to the tetracation in the dark by allowing oxygen gas into the system. This reversible process is marked by the disappearance of naphthalene fluorescence as the molecule is recomplexed by the tetracationic cyclophane. This supramolecular system can be chemically modified such that the pi-electron-rich unit, either a naphthalene derivative or a hydroquinone ring, and the tetracationic cyclophane are covalently linked, We have demonstrated that the pi-electron-rich residue in this system is totally ''self-complexed'' by the cyclophane to which it is covalently attached. Additionally, the self-complexation can be switched ''off'' and ''ion'' by electrochemical two-electron reductions and oxidations, respectively, of the tetracationic cyclophane component, Thus, we have achieved the construction of two switches at the nanoscale level, one driven by photons and the other by electrons.