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Metals in Passive State1 Yu. A. Popov Karpov Institute of Physical Chemistry, ul. Vorontsovo Pole 10, Moscow, 103064 Russia Received November 17, 2003 Abstract — A theoretical model [1–4] of the passive state of metals is discussed. This model considers hopping migration of ionic components in the passive layer (PL) lattice, which delivers reactants to take part in interphase processes at PL boundaries with metal and electrolyte, thus binding the latter kinetically and structurally, and defines the dependence of lattice point defectiveness on the potential. The defectiveness results in the transpassivity transition, i.e., the finiteness of the passivity range. A theoretical model of passivity should involve (predict) the transpassivity transition. This serves as a criterion of its consistence. Nonlinear equations of hopping migration in a strong electric field that violates the Ohm law are generalized. Their solution provides a more precise expression for PL point defectiveness and its dependences on the anodic potential, current density, and other parameters. An expression for transpassivity potential that was shown to linearly depend on the defec-tiveness is derived. A model describing formation of new PL elementary oxide cells at PL–metal interface, i.e., the “processing” of metal to give passivating oxide is generalized. This process compensates the electrochemical dissolution of PL at the solution boundary. The process of PL origination is also considered, namely, its crystallization in the prepassive range by the mechanism of two-dimensional nucleation of oxide.
15/12/2008 | 1240 Посещения | Печать
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Protective Coatings of High-Melting Compounds of IV VIA Group Metals Plated from Ionic Melts (Review) V. V. Malyshev National Ukrainian University of Technology “Kiev Polytechnical Institute,”
Prosp. Pobedy 37/4, Kiev-56, 03056 Ukraine e-mail: mailto:
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Received October 1, 2001; in final form, April 5, 2004 Abstract — Brief historical review of the high-temperature electrochemical syntheses (HES) of protective coatings from ionic melts is given. The modern state of the branch and the problems met by the HES in producing high-melting compounds of IV–VIA group metals from ionic melts are considered.
15/12/2008 | 1234 Посещения | Печать
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The Classification System of ISO 9223 Standard and the Dose Response Functions Assessing the Corrosivity of Outdoor Atmospheres A. A. Mikhailov*, J. Tidblad**, and V. Kucera** * Institute of Physical Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia ** Swedish Corrosion Institute, Roslagsvagen 101,
hus 25, SE-104 05 Stockholm, Sweden Received June 9, 2003 Abstract — The ISO 9223 Standard “Corrosion of Metals and Alloys–Corrosivity of Atmosphere–Classifica-tion” which is now in force was based on the data obtained mainly in thetemperate climate of Europe and North America. At present, it is being revised by using data from new programs of atmospheric tests carried out in cold, temperate, subtropical, and tropical climates. The paper tackles problems of assessing the atmospheric corrosivity from the environmental parameters. A model and dose–response functions characterising the corrosivity of the outdoor atmospheres are described. Suggestible ways of possibly improving the standard with the use of the functions derived are considered.
15/12/2008 | 1207 Посещения | Печать
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Electrodeposition of a Cu Cd Alloy in the Presence of Surfactant Mixtures from Several Reaction Series S. P. Shpan’ko, V. P. Grigor’ev, and O. V. Dymnikova Rostov State University, ul. Zorge 7, Rostov-on-Don, 344090 Russia Received November 26, 2003 Abstract — The effects of one- to four-component mixtures of organic compounds from four reaction series on the currents and potentials of the electrodeposition of a Cu–Cd alloy were studied. The revealed correlation between the deposition parameters of compositionally different alloys and their constituents, on one hand, and the total polarity of substituents in surfactant molecules, on the other hand, was interpreted in terms of the Linear Gibbs Energy Relation.
15/12/2008 | 1151 Посещения | Печать
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Corrosion-Electrochemical Behavior of Nickel Monosilicide in Alkaline Electrolyte A. B. Shein and I. L. Sergeeva Perm State University, ul. Bukireva 15, Perm, 614990 Russia e-mail:
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Received April 28, 2003 Abstract — Corrosion-electrochemical behavior of compact and powder electrodes of nickel monosilicide (NiSi) and pure Ni and Si in 0.1–5.0 M NaOH solutions is studied by using steady-state and cyclic voltammetry. The main regularities of NiSi anodic dissolution are revealed. It is shown that, in spite of the fact that Si solubility increases with an increase in the pH value, nickel monosilicide exhibits a high anodic resistance due to the protective properties of surface Ni(OH)2 . At high anodic potentials, Ni(OH)2  NiOOH reversible conversion takes place.
15/12/2008 | 1146 Посещения | Печать
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Anodic Dissolution of Cobalt Silicides in Alkaline Electrolytes A. B. Shein and I. L. Sergeeva Perm State University, ul. Bukireva 15, Perm, 614990 Russia Received December 16, 2003 Abstract — Anodic dissolution of cobalt silicides Co2Si, CiSi, CoSi2, CoSi2–Si (eutectic alloy), and also individual Co and Si in 0.1–5.0 N NaOH solutions is studied by using cyclic voltammetry (CVA). In alkaline electrolyte, despite the increasing activity of silicon, the electrode is passivated due to the formation of protective films of cobalt oxides and hydroxides. The anodic stability of cobalt increases with a decrease in metal content.
15/12/2008 | 1107 Посещения | Печать
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Estimating Corrosion Current and Tafel Constants from the Curvature of Voltammetric Curves Near the Free-Corrosion Potential V. S. Beleevskii*, K. A. Konev*, V. V. Novosadov**, and V. Yu. Vasil’ev** * DOAO ORGENERGOGAS Enterprise for Organization and Operation
of Power-Mechanical Equipment in Gas Industry e-mail:
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** Moscow State Institute of Steel and Alloys (Engineering University),
Leninskii pr. 4, Moscow, 119991 Russia Received October 24, 2003 Abstract — Application of calculating the electrochemical corrosion parameters from direct polarization measurements near the free-corrosion potential is discussed. The reliability of indirectly determining corrosion currents and Tafel coefficients is estimated. The error is determined as a geometric sum of the effects taking into account the root-mean-square deviations of measured currents and polarization.
15/12/2008 | 1167 Посещения | Печать
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A Geometrical Model of a Glass Enamel Coating. Part 1. Calculation of the Open Surface Fraction of Enameled Metal N. T. Shardakov and V. Ya. Kudyakov Institute of High-Temperature Electrochemistry, Ural Division, Russian Academy of Sciences,
ul. S. Kovalevskoi 20, Yekaterinburg, 620219 Russia Received May 14, 2003 Abstract — A geometrical model of glass–enamel coating (GEC) is proposed. Gas bubbles are chosen as the basic elements of its macrostructure, and the fundamental principles of the model are formulated. A model equation correlating the fraction of the open metal surface with the dissolution depth of enamel and GEC parameters is derived. Partial equations are derived according to various laws of the bubble size distributionsuch as invariance of the size, equal probability of any size, and normal, or lognormal distribution of bubbles over the size. It is shown that the open surface fraction always increases with the concentration of bubbles and contact angle, whereas its dependence on the GEC thickness and the statistical characteristics of the totality of bubbles has a more complex character.
15/12/2008 | 1105 Посещения | Печать
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The Effect of Thermal Preoxidation on the Pitting Susceptibility of Steel X18 H10T T. Yu. Zimina, O. G. Tselykh, and E. K. Oshe Institute of Physical Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia e-mail:
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Received August 27, 2003 Abstract — The effect of thermal preoxidation of a  18 10 stainless steel in air at temperatures of 100 to 775°C on its susceptibility to pitting is studied. It is shown that the pitting potential of steel depends on the number of defects in the preformed surface thermooxides. Oxidation at 100–300°C forming rhombohedral oxides of  -(Fe,Cr)2O3 type with a small deviation from stoichiometry decreases the pitting susceptibility. Oxidation at higher temperature impairs the corrosion resistance of steel.
15/12/2008 | 1126 Посещения | Печать
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Fe
Ni Bronze in Chloride Electrolyte1 
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9-4-4-1 castbronze in 0.5 N NaCl + 0.01 N HCl was studied. X-ray diffraction analysis revealed that the Fe3Al and 
1-phases present at the surface of the initial bronze become predominantly etched during the early period of anodic dissolution at E = –0.12 V (NHE). According to electrochemical and analytical data, the above phases dissolve at this potential most rapidly. The x-ray diffraction data agree well with the results obtained by atomic absorption analysis of the solution.