Atomic-topographic model of the electrochemical dissolution of a solid metal taking into account the effect of point lattice defects

A topokinetic model of a dissolving solid metal containing point defects, that is, either admixture atoms of a substantially more lowly or highly corrosion-resistant metal or the crystal lattice vacancies, is proposed. The model takes into account the mutual consistency of the atomic relief and the dissolution rate. Similarly to a defect-free crystal, the steady-state dissolution rate is determined by the elementary acts of transferring the base atoms to solution from step kinks whose amount substantially depends on the concentration of the point defects. Original Russian Text ? Yu. V. Alekseev, G.Yu. Alekseev, I.Yu. Alekseev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 479–487.     

Passivating film as a structured solid solution of the alloy oxide particles. The structuring effects (Ordering and Stratifying)

The investigations deal with the passivating films that can be modeled as a solid solution of the alloy oxides. Models of unstructured (regular) solutions enable one to explain the dependence of the dissolution rate of a Fe-Cr alloy at a chromium concentration higher than 0.2 atomic parts. Irregular solution models, which take into account the alloy structuring due to the interactions between its components is applicable to the compositions below a chromium content of 0.2. The physical effects predicted by the model are studied, namely the higher dissolution rate of the alloy compared to the dissolution rate of the most active component, the different alloying mechanisms at the different kinds of interactions between the components, as well as the kinetic metastability and its role in the initiation of pitting by some admixtures. Original Russian Text ? Yu.V. Alekseev, I.Yu. Alekseev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 4, pp. 346–359.     

2D Atomic-Topological Model of the Dissolution Kinetics of a Metallic Crystal: Typical Atomic Relief Positions and Fragments

The atomic-topological kinetics problem of the self-consistency between the dissolution kinetics and the atomic relief of the dissolving boundary is solved for an imaginary two-dimensional crystal in two ways: (i) in terms of the model of atomic positions determined by the number of the nearest neighbors and (ii) in terms of the typical atomic relief structures (steps, kinks, etc.). To a sufficient accuracy, the results provided by these two models coincide. The approaches developed are aimed at solving the problem of the dissolution of an actual three-dimensional crystal.__________Translated from Zashchita Metallov, Vol. 41, No. 3, 2005, pp. 244–257.Original Russian Text Copyright © 2005 by G. Alekseev, Yu. Alekseev, Bityurin.     

Statistical aspect of the independence principle of heterogeneous reactions taking into account the surface state

The independence principle of electrode reactions is shown to be no more than a particular example of the theoretical-probabilistic regularities determined by the statistical nature of a large scope of systems studied by the chemical kinetics. It does not exclude but explains the possible mutual effect of different reactions on each other. In the case of a mass exchange between a structured solid and a solution or a gas, the independence principle should be formulated in terms of the superficial atom positions determined by the number of close neighbors. Original Russian Text ? Yu. V. Alekseev, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 339–347.     

Development or Stagnation of the Theory of Metal Passivity

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. __________ Translated from Zashchita Metallov, Vol. 41, No. 5, 2005, pp. 528–543. Original Russian Text Copyright ? 2005 by Alekseev.     

Determining the integral dissolution rate of two-phase alloys in cryolite-alumina melts

Electron microscopy and x-ray diffraction analysis are used in studying Cu-Fe and Ni-Fe-Al alloys upon their anodic polarization in a cryolite-alumina melt, thus, clarifying the regularities of their dissolution and the formation of oxide coatings. Based on the results obtained, a technique of determining the integral corrosion rate of the alloys is proposed. Original Russian Text ? A.Yu. Filatov, E.V. Antipov, M.I. Borzenko, S.Yu. Vasil’ev, V.M. Denisov, V.V. Ivanov, S.M. Kazakov, Z.V. Kuz’minova, V.K. Laurinavichyute, V.V. Lunin, D.A. Simakov, V.I. Shtanov, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 664–668.     

The effect of atomic hydrogen on the anodic dissolution of iron in a sulfate electrolyte studied with impedance spectroscopy

Impedance spectra of an iron membrane electrode are recorded in a range of the active metal dissolution potentials in an acidic sulfate solution. The rate constants of the elementary adsorption stages of iron dissolution are found to decrease with an increase in the amount of atomic hydrogen. This results in a decrease in the metal surface coverage with intermediate particles of the anodic process. Original Russian Text ? M.A. Maleeva, A.A. Rybkina, A.I. Marshakov, V.V. Elkin, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 587–595.     

Model concepts on the mechanism of microarc oxidation of metal materials and the control over this process

Based on a critical analysis of literature data, new model concepts on the mechanism of microarc oxidation (MAO) are developed. The correctness of these model concepts is confirmed by experimental results on the average growth rate of oxide-ceramic coatings for different duration of the MAO process on AД31, MA2-1, and MЛ-5 alloys, the morphology of the surface structure of coatings of different thickness, the comparative electrical strength of dielectric coatings, which is assessed during self-quenching of the MAO process and in air. Equivalent electric circuits developed describe this process and are experimentally shown to be the “tool” which allows controlling MAO of aluminum and magnesium alloys. Original Russian Text ? A.G. Rakoch, V.V. Khokhlov, V.A. Bautin, N.A. Lebedeva, Yu.V. Magurova, I.V. Bardin, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 2, pp. 173–184.     

Anodic dissolution of ferrite phases from iron-carbon ferrite-cementite alloys with different forms of cementite

Methods of electrochemical analysis, metallography and mathematical statistics are applied to calculate the ferrite anodic dissolution rate from both the independent structural constituent and the subconstituent in lamellar or granular pearlite. The higher dissolution rate of the former compared to the latter is caused by the structure peculiarities. Original Russian Text ? S.N. Saltykov, N.V. Tarasova, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 5, pp. 542–547.     

Relaxation processes and kinetics of the thermal oxidation of Ni-Mo-B alloys obtained by chemical catalytic reduction

Kinetics of the high-temperature oxidation of Ni-Mo-B alloys containing 11 wt. % Mo (obtained by means of chemical catalytic reduction with the use of dimethylamine borane) is investigated. A strong dependence between the oxidation rate and the sublimation of volatile compounds on the prehistory of deposits is disclosed. Freshly obtained deposits exhibit an anomalous short-term weight loss caused by the “explosive” character of the removal of water vapors, evolved as a result of the reduction of molybdenum and boron oxides with hydrogen at heightened temperatures. Preliminarily heating the specimens in a vacuum decreases the intensity of or completely eliminates the anomalous phenomenon. When oxidizing the coatings in air at 600°C, two processes take place, namely, the oxidation of the coating components (a growth of the oxide layer) and the sublimation of volatile compounds. Original Russian Text ? V.A. Arslambekov, A.B. Drovosekov, M.V. Ivanov, V.M. Krutskikh, E.N. Lubnin, B.F. Lyakhov Yu.M. Polukarov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 1, pp. 13–20.     

The effect of phosphonates on the corrosion of carbon steel in heat-supply water

The effect of phosphonates used in Russian heat-power engineering on the corrosion of carbon steel in deaerated delivery water at 90°C is studied. It is shown that introduction of phosphonates reduces the susceptibility of steel to local corrosion. A zinc complex of hydroxyethylidenediphosphonic acid (OEDP-zinc) is the most effective inhibitor of the anodic reaction. Original Russian Text ? Yu. V. Balaban-Irmenin, A.M. Rubashov, N.G Fokina, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 2, pp. 146–149.     

Zinc-and aluminum-based protective coatings obtained in a fluidized bed

Sherardizing and zinc-aluminizing Ct3 steel in a fluidized bed are considered. Microhardness, microbrittleness, porosity, and corrosion resistance of zinc coatings are analyzed. Original Russian Text ? Yu.A. Balandin, A.S. Kolpakov, E.V. Zharkov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 379–382.     

Dissolution mechanism and partial electrode processes at infralow frequency AC polarization of brasses in chloride media. I. α-brass Cu20Zn

Being typical of a steady-state anodic polarization, the uniform dissolution of α-brass Cu20Zn is retained for the anodic half-period in the pulsed mode (f = 0.17 Hz). At such an ac polarization, the dissolution is alternated with the copper deposition in the cathodic half-periods to form a loose fine-grain deposit at the electrode. Under severe hydrodynamic conditions, no copper deposit is formed. With an increase in the current in the cathodic half-periods, the pH of a near-electrode solution layer increases, thus changing the anodic processes. Namely, the oxidation of brass components to soluble chloride complexes gives place to the formation of poorly soluble products. Original Russian Text ? I.K. Marshakov, O.Yu. Kuksina, V.Yu. Kondrashin, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 128–134.     

Video in-situ observation of the free corrosion of an Al-1Sn sacrificial alloy in sodium sulfate

Some peculiarities of the Al-1Sn alloy corrosion in sodium sulfate solution were investigated by applying video-observation in-situ. As a result of the free corrosion the inclusions of almost pure tin were revealed and identified with the use of a scanning electron microscope. The hydrogen evolution occurs just at the inclusions. Original Russian Text ? A.V. Goncharov, Yu.Ya. Andreev, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 5, pp. 548–550.     

New corrosion-resistant electrodes: Synthetic diamond and diamond-based materials. The semiconductor and structure aspects—a review

Specific features of electrode behavior of synthetic diamond and diamond-based materials (in particular, diamond-nondiamond carbon nanocomposites, nanocrystalline diamond, and diamond-like carbon) are reviewed. Effects of the crystal structure and semiconductor nature of diamond on its electrochemical properties are discussed. Original Russian Text ? Yu.V. Pleskov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 2, pp. 115–131.     

Phase nanotomography in the superficial layers

A method of phase nanotomography and spectral multiplexing for a nondestructive monitoring of the nanoscale disturbance of refractive index distribution across the nonuniform near-electrode layer at a metal/solution interface is analyzed. It is shown that the amplitude Fourier-spectroscopy of reflection from the nonuniform near-electrode layer with a weak (nanoscale) disturbance of the complex refractive index profile, and weak optical parameters dispersion makes one realize the multiplex principle of measuring and reconstructing the refractive index (and hence, the concentration) distribution across the near-electrode solution layer by using either interference pattern or additional Fourier-transform. Combining the multiplex reconstruction of a three-dimensional profile of the dissolved-products layer and the standard Fourier-spectroscopy allows in situ controlling both the metal dissolution intensity at any point of its surface and the metal dissolution product composition over each section of the near-electrode layer. Original Russian Text ? V.A. Kotenev, D.N. Tyrin, A.Yu. Tsivadze, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 5, pp. 490–497.     

The aftereffect of cyclic loading on the corrosion of aluminum-based alloys

Effects of bench loading and stresses on the corrosion resistance of д16AT alloy are studied. Complicated effect of the stress intensity and the cyclic loading on the surface morphology and pit concentration is demonstrated. Harmonic character of the loading dependence of the change of corrosion resistance is due to segregation effects. Original Russian Text ? V.Yu. Vasil’ev, V.S. Shapkin, N.V. Barulenkova, M.V. Antonova, and E.N. Antonova, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 227–232.     

The effect of anionic composition of electrolytes on the anodic dissolution of iron-family metals

The anodic dissolution rate of the iron-family metals is analyzed depending on the anionic composition of aqueous electrolyte solutions. Investigation of the process in a broad range of potential values (including the limiting current range) in solutions with the controlled content of cations and anions enables us to discover the diffusion limitations at a stage of anion supply to the electrode-electrolyte interface and show the importance of processes in the electrolyte layer near the electrode. During the anodic process, anions, which are present in the solution, act not only as counterions balancing for change balancing of the positive metal ions formed at the interface, but also as depolarizers of the anodic process. Upon the formation (or at the moment of appearance), metal ions interact with the anions to form ion pairs that may exist and move independently. The supply of “free” anions to the electrode surface controls the process rate in the limiting current range. Original Russian Text ? D.A. Tkalenko, Yu.P. Vishnevskaya, M.V. Byk, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 4, pp. 445–448.     

Determining the partial currents of silver ionization, its oxide formation, and chemical dissolution by multicycle chronoammetry with an RRDE

A multicycle chronoammetry with a rotating disc electrode with a ring (RRDE) enables one to experimentally discriminate between the partial currents of the substrate metal ionization, anodic formation of the oxide, and chemical dissolution of the oxide in the summary polarization current of the disc. The technique is approved by an example of Ag|Ag₂O|OH⁻(H₂O) system. In a range of relatively small anodic potentials of the Ag disc (0.48 to 0.51 V), the active dissolution of silver at the open surface sites and via pores in the surface film dominates; the phase formation current and, accordingly, the current efficiency of the process rapidly drop. At the potentials of the voltammogram maximum (0.52 to 0.53 V) when the silver active dissolution current is suppressed, the phase formation currents prevail and substantially exceed the chemical dissolution rate of the oxide. The thickness of an Ag₂O film rapidly increases under these conditions, and the current efficiency of the oxide formation is close to 100% for the whole polarization period. The rate constant of the chemical dissolution of an Ag(I) oxide is practically independent of the anodic phase-formation potential, but slightly depends on the oxide film thickness, reflecting changes in the film structure and, possibly, in its composition, from AgOH to Ag₂O. Original Russian Text ? D.A. Kudryashov, S.N. Grushevskaya, A.V. Vvedenskii, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 3, pp. 321–330.