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31.
On the Local Inner Corrosion of Oil and Gas Pipelines in the West-Siberian Fields and Its Prevention A. A. Gonik GUP Institute of Problems of Energy-Resources Transportation,
pr. Oktyabrya 144/3, Ufa, 450055 Russia e-mail:
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Received November 23, 2004 Abstract — The sources of corrosion grooving of inner surface of pipes in the West-Siberian oil and gas pipelines is analyzed. A possible way of preventing this local corrosion is to hydraulically increase the aggregative stability of the pumped-through emulsion. For this purpose, stratal water should be actively stirred in lower segments of the pipelines.
23/09/2008 | 836 Посещения | Печать
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32.
Development or Stagnation of the Theory of Metal Passivity Yu. V. Alekseev Karpov Institute of Physical Chemistry, ul. Vorontsovo Pole 10, Moscow, 103064 Russia e-mail:
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Received August 17, 2004 Abstract — Methods and approaches of physicochemical modeling, as well as the adequacy of the mathematical apparatus used for constructing two variants of the theory of a passively dissolved metal state are compared. Their essential differences are noticed only as a background, while their contents are discussed chiefly in view of their applicability to solving the problem formulated. The first approach presented in the works of Yu.A.Popov and coworkers declares the adherence to the theory of K. Fetter based on the hypothesis about the equilibrium oxygen exchange between the oxide and solution. The second approach developed in the kinetic–electrostatic model of Ya.M. Kolotyrkin and Yu.V. Alekseev rejects this hypothesis and assumes that of all the processes in the domain between the metal and solution are equally important. For disproving our concept, the opponents suggest a “developed Fetter’s model.” The results obtained in this approach and their adequacy are the main object of this investigation.
23/09/2008 | 853 Посещения | Печать
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33.
Factors Influencing the Long-term Corrosion of Bronze Artefacts in Soil1 A. G. Nord, E. Mattsson, and K. Tronner National Heritage Board, P.O. Box 5405, SE-11484 Stockholm, Sweden e-mail:
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Received January 5, 2005 Abstract — The investigation was undertaken to determine the main factors causing deterioration of bronze objects in soil by studying artefacts from archaeological excavations in progress. Objects that had been buried for 300–3000 years were examined. The composition of the metal, corrosion products, and surrounding soil was determined by chemical analysis. The possible effect of polluting sources and the environment in general was also taken into account. In total, 82 variables were coded, and their effects were statistically evaluated by multivariate analysis. Acidic soil, large deposits of sulfur pollutants in relation to the critical load, the presence of soot and soluble salt, and conditions giving access to water and air were found to accelerate the deterioration. A major part of the corrosion is likely to have occurred during the latest century. The results are of importance for the understanding and estimation of long-term corrosion of bronze objects in soil. Key words: bronze corrosion, long-term corrosion, environment, soil acidity, multivariate analysis.
23/09/2008 | 1193 Посещения | Печать
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34.
Marine Corrosion and Protection of Aluminum Alloys According to Their Composition and Structure V. S. Sinyavskii and V. D. Kalinin All-Russian Institute of Light-Weight Alloys (OAO), ul. Gorbunova 2, Moscow, 121596 Russia e-mail:
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Received August 19, 2004 Abstract — Based on long-term tests of aluminum alloys in seawater of various climatic zones from the Arctic to the tropics, the peculiarities of their corrosion behavior are revealed. In contrast to other alloys, hydrogen sulfide has a beneficial effect on their corrosion resistance due to the passivation. However, deep in the Black Sea, the alloys, which are susceptible to structural types of corrosion, were subjected to strong exfoliation corrosion, because hydrogen sulfide excluded fouling with microorganisms that inhibits exfoliation corrosion. Alloys of the Al–Mg system exhibit the highest corrosion resistance in seawater. Alloy of an    61 type ( ul= 340 MPa, 0.2 = 180–210 MPa,  = 11–15%) has shown a good performance. Alloying with scandium and ther-momechanical treatment make possible further simultaneous improvement of mechanical properties and corrosion resistance. It is shown that crevice corrosion is more typical of corrosion-resistant low aluminum alloys possessing lower free-corrosion and pitting potentials compared to high alloys, which are susceptible to structural types of corrosion, in particular, exfoliation corrosion. The methods of the aluminum alloys protection against marine corrosion are considered. It is shown that, in contrast to carbon steels, the anodic–cathodic protection is used for aluminum alloys.
23/09/2008 | 1278 Посещения | Печать
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35.
Solid-Phase Diffusion at a Potentiostatic Dissolution of Silver Alloyed with Gold O. A. Kozaderov, O. V. Sazhneva, O. V. Koroleva, and A. V. Vvedenskii Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia e-mail:
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Received August 17, 2004 Abstract — In an acidic nitrate solution containing no less than 10–4 mol/l Ag+, potentiostatic anodic dissolution of silver from its alloy with gold (up to 35 at. %) already in about 10 s is limited by the solid-phase mutual diffusion of the components. A number of diffusion-kinetic dissolution models taking into account contribu-tions from the liquid-phase mass transfer, segregation in the surface layer, microroughness of the surface, shift of the alloy–solution interface, as well as the relaxation of nonequilibrium vacancies into a transient dissolution current are considered. The diffusivities and mutual diffusivities of the components, concentrations of nonequilibrium vacancies, and thickness of the diffusion zone estimated in terms of these models are compared. The effect of the overpotential and alloy composition is discussed. The main source of nonequilibrium monovacancies in the amount 14 orders as high as the equilibrium one is found to be the dissolution of silver. The efficiency of the sinks, among which the formation of bivacancies seemingly dominates, is not high, which predetermines the slowness of relaxation processes in the solid-phase diffusion zone.
23/09/2008 | 1314 Посещения | Печать
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36.
The Effect of Sodium Thiocyanate on the Corrosion Dissolution Rate of Silver in Thiosemicarbazide Solutions L. F. Kozin and B. I. Danil’tsev Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Akad. Palladina, 32/34, Kiev-142, 03680 Ukraine e-mail:
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Received February 18, 2003 Abstract — The effect of thiocyanate on the corrosion dissolution rate of silver in thiosemicarbazide (TSC) ammonium–chloride–bromide solutions was studied by using gravimetry and rotating disc electrode technique. The corrosion dissolution of silver was shown to be preceded by the formation of dithiosemicarbazide molecules due to the oxidation with iron (III) ions. The “second ligand” phenomenon is discussed, which consists in an increase in the corrosion dissolution rate of silver upon adding sodium thiocyanate (STC) to a TSC solution because of the decrease in the adsorption layer thickness. A synergism was discovered in the case of the corrosion dissolution of silver in a solution containing both thiosemicarbazide and sodium thiocyanate. The composition of the adsorption layer formed on a silver electrode and involving silver, sulfur (AgHS and Ag2S), as well as carbon, nitrogen, and oxygen forming the base of adsorption layers, was investigated by means of Auger spectrometry. The kinetic parameters (rate constants and reaction orders) were determined and a mechanism of the corrosion dissolution of silver in TSC, STC, and TSC + STC solutions is proposed.
23/09/2008 | 1239 Посещения | Печать
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37.
The Mechanism of the Cobalt Anodic Ionization in Chloride Solution F. D. Manilevich, L. F. Kozin, A. K. Bogdanova, and B. I. Danil’tsev Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Palladina 32/34, Kiev, 03680 Ukraine e-mail:
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Received March 18, 2004 Abstract — The mechanism of the cobalt anodic ionization in 2.5 M CoCl2 solution (pH 3.5   0.2, t = 15–60°C) is studied with the use of rotating disk electrode and rotating ring–disk electrode methods. The experimental data showed that the ionization proceeds by stages, of which the first is an intermediate CoAads species formation (A is Cl– or OH–), in which the cobalt oxidation state is 1+. Further CoAads transformation involves rapid parallel reactions of the Co+ ions electrochemical oxidation or disproportionation. An oxidation current wave was revealed at the platinum ring electrode for the species formed during the cobalt anodic ionization at the disk electrode. Judging by the wave potential, these species can be either finely dispersed elemental cobalt or the intermediate Co+ ions.
23/09/2008 | 1253 Посещения | Печать
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38.
Electropolishing of Silver in Water Organic Solutions of Potassium Thiocyanate A. V. Balmasov*, E. V. Koroleva*, and S. A. Lilin** * Ivanovo State University of Chemistry and Technology,
pr. F. Engel’sa 7, Ivanovo, 153000 Russia ** Institute of Chemistry of Solutions, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia Received August 19, 2004 Abstract — The anodic behavior of silver in aqueous and water–glycerol solutions of potassium thiocyanate is studied on motionless and rotating-disk electrode. The appearance of the limiting current is explained. Optimal solution compositions and conditions for the process (which ensure metal polishing) are suggested.
23/09/2008 | 1265 Посещения | Печать
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39.
Corrosion of Hydrides of Nickel and Cu30Ni Alloy in Oxygen Containing Solutions G. N. Markos’yan, D. S. Sirota, and A. P. Pchel’nikov Karpov Institute of Physical Chemistry State Scientific Center of the Russian Federation,
ul. Vorontsovo Pole 10, Moscow, 103064 Russia e-mail:
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Received July 27, 2004 Abstract — Corrosion behavior of nickel hydride is studied in alkaline, neutral, and weakly acidic oxygen-containing solutions by compensating oxygen consumed in corrosion and spectrophotometric analysis of solution for nickel. It is shown that in the course of nickel hydride corrosion in alkaline solutions, oxygen is consumed solely in its interaction with hydrogen formed at hydride decomposition, while nickel remains at the surface. It is concluded that, in a pH range from 7 to 14, hydrogen oxidation is limited by its solid-phase diffusion, whereas the rate of nickel hydride decomposition is pH-independent. The difference in the corrosion behavior of the original alloy and its hydride is attributed to the fact that the original alloy evolves copper ions, whereas the hydride evolves hydrogen.
23/09/2008 | 1258 Посещения | Печать
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40.
Electrochemical Estimation of Developed Roughness of Galvanic Nickel CoatingsA. N. Podobaev*, S. S. Kruglikov**, P. Becker***, and M. Mattiesen*** * Karpov Institute of Physical Chemistry, State Scientific Center of the Russian Federation
ul. Vorontsovo Pole 10, Moscow, 103064 Russia e-mail:
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** Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125190 Russia *** Tyco Electronics Corp., Menlo Park, California, USA Received April 2, 2004 Abstract — The roughness of nickel coatings with highly developed surface (constituted from dendrites) can be estimated by measuring their differential capacitance under cathodic polarization in weakly acid sulfate solution. For the same purpose, using diffusion- or kinetics-controlled electrochemical reactions yields underestimates.
23/09/2008 | 1227 Посещения | Печать
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