Showing papers in "Protection of Metals in 2006"
TL;DR: In this article, new model concepts on the mechanism of microarc oxidation (MAO) are developed based on a critical analysis of literature data, and 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
Abstract: 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.
64 citations
TL;DR: In this article, the surface of a carbonyl iron powder was chemically modified with functional triethoxysilanes and ethyl n-alkylphosphonates, and the grafted layers were examined by x-ray photoelectron spectroscopy and conductivity measurements.
Abstract: The surface of a carbonyl iron powder was chemically modified with functional triethoxysilanes and ethyl n-alkylphosphonates. The grafted layers were examined by x-ray photoelectron spectroscopy and conductivity measurements.
27 citations
TL;DR: In this paper, a polymeric additive of the nonionogenic type N1 (3 × 106 g/mol) is proposed, which favors the deposition of chromium coatings that have good adhesion to the surface, do not crack and have a thickness of several tens micrometers.
Abstract: The effect of certain water-soluble synthetic polymers on the current efficiency, the kinetics of partial cathodic reactions, and certain properties of coatings at the chrome plating from sulfate-formate baths based on Cr(III) salts is studied. A polymeric additive of the nonionogenic type N1 (3 × 106 g/mol) is proposed, which favors the deposition of chromium coatings that have good adhesion to the surface, do not crack, and have a thickness of several tens micrometers. It is found that the polymers have an accelerating effect on the aggregation of the particles of the chromium-hydroxide sol formed in the near-electrode layer, which, apparently, improves the deposit quality and enhances the current efficiency. It is shown that the resulting amorphous-crystalline chromium deposits are sufficiently hard and exhibit good protectiven ability at the anodic dissolution in aggressive media.
21 citations
TL;DR: In this article, the metal potentials with the polarization curves recorded in soil electrolytes at pH values typical of the near-electrode soil layer were used to predict the character and rate of the corrosion process.
Abstract: Electrochemical equipment, which enables one to study the processes of underground corrosion under conditions of differential aeration of soils, with no limitation of the experiment duration at a fixed position of the interface boundary and controlled moisture content, is developed. The character and rate of the corrosion process can be predicted by comparing the metal potentials with the polarization curves recorded in soil electrolytes at pH values typical of the near-electrode soil layer. The usage of solely gravimetric technique in studying the above corrosion processes may provide wrong results.
19 citations
TL;DR: In this paper, the effect of the corrosion product layer on the surface potential and capacitance of the zinc surface was studied, and the spatial separation of the cathodic and anodic reactions was noticed in the profiles of the electrode potential and chemical composition of corrosion products (infrared microscopy).
Abstract: Scanning vibrating capacitor (Kelvin probe) and electrochemical impedance spectroscopy are used in electrochemical monitoring of the atmospheric corrosion of zinc. The effect of the corrosion product layer on the surface potential and capacitance is studied. Upon the local application of NaCl, the spatial separation of the cathodic and anodic reactions was noticed in the profiles of the electrode potential and chemical composition of the corrosion products (infrared microscopy). The effect of corrosion inhibitors and activators on the electrochemical atmospheric corrosion of zinc is studied.
17 citations
TL;DR: In this paper, the electrolyte and parameters of highvoltage anodic-cathodic process, which enable one to apply rather thick (to 340 μm) oxide coatings to titanium alloys, are selected.
Abstract: The electrolyte and parameters of high-voltage anodic-cathodic process, which enable one to apply rather thick (to 340 μm) oxide coatings to titanium alloys, are selected. Characteristics of the coating formation on aluminum and titanium alloys are compared. It is found that, on the titanium alloys, the stage of microarc discharges occurs only at relatively high anodic and cathodic components of the current density. The voltage chronograms and oscillograms also have pronounced specific features.
14 citations
14 citations
TL;DR: In this article, the effect of hydrofluoric acid on the cathodic reduction of molybdate ions is studied and it is shown that the mechanism of this process is determined by the acid concentration.
Abstract: The effect of hydrofluoric acid on the cathodic reduction of molybdate ions is studied. It is shown that the mechanism of this process is determined by the acid concentration: in a concentration range below 25 g/l the intermediate products of molybdate-ion reduction, namely, black or colored deposits containing molybdenum with the average valence of 3.6–4 are formed on the cathode. For the concentration above 50 g/l, molybdate ions are completely reduced and form at the cathode dense light metallic coatings with a thickness of 3–5 μm and good adhesion to the substrate. The addition of hydrofluoric acid prevents polymerization of molybdate ions.
13 citations
TL;DR: In this article, specific features of electrode behavior of synthetic diamond and diamond-based materials (in particular, diamond-nondiamond carbon nanocomposites, nanocrystalline diamond, and diamondlike carbon) are reviewed.
Abstract: 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.
12 citations
TL;DR: In this paper, the effect of phosphonates used in Russian heat power engineering on the corrosion of carbon steel in deaerated delivery water at 90°C was studied, and it was shown that the introduction of a zinc complex of hydroxyethylidenediphosphonic acid (OEDP-zinc) is the most effective inhibitor of the anodic reaction.
Abstract: 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.
11 citations
TL;DR: In this article, the effects of commercial corrosion inhibitors (VNPP-2V, KI-1, and IKU) in fluids used for acid treatments of oil wells were studied by gravimetric and electrochemical measurements.
Abstract: Protective effects of some commercial corrosion inhibitors (VNPP-2V, KI-1, and IKU) in fluids used for acid treatments of oil wells were studied by gravimetric and electrochemical measurements. The inhibitors were tested in the presence of Fe3+ ions and in “aged” inhibited fluids.
TL;DR: In this article, the composition of yellow bronze coatings deposited from acidic sulfate solutions added with polyether laprol and the electrodeposition conditions are studied by voltammetry and XPS.
Abstract: The composition of yellow bronze coatings deposited from acidic sulfate solutions added with polyether laprol and the electrodeposition conditions are studied by voltammetry and XPS. It is found that halides in rather low (micromolar) concentrations affect significantly the partial electrodeposition processes. Chlorides increases cathodic polarization, widen the current window of the yellow bronze electrodeposition, and favor the increase in tin content of the coatings. Bromides narrow the current window, lower the tin content in the coatings, and hinder the yellow bronze surface oxidation. Iodides inhibit the copper electroreduction markedly, which makes the yellow bronze deposition practically impossible.
TL;DR: In this paper, the microhardness of chromium-graphite composite coatings is investigated in Cr(III)-baths modified with disperse phases of CeO2, Cr2O3, graphite, and ultradisperse diamond.
Abstract: Chromium electroplates from Cr(III)-baths modified with disperse phases of CeO2, Cr2O3, graphite, and ultradisperse diamond are studied. Mechanical properties of the composite coatings are investigated. The Cr2O3-particles present in the bath are found to cause the destruction of the coatings already during the plating. When modifying with CeO2-particles, good coatings with enhanced microhardness can be obtained at their concentration in the bath of no more than 15 g/l. The deposition rate in such cases exceeds that in the blank baths. The optimum range of the CeO2-particle concentration, allowing to obtain the maximal microhardness, is 5–8 g/l. The self-lubricating chromium-graphite composite coatings can be deposited at a graphite concentration in the bath of up to 4 g/l. The microhardness of the chromium coatings is most strongly affected by ultradisperse diamond particles that increase the microhardness by a factor of 1.4; they also decrease the coatings’ brittleness. When the ultradisperse diamond concentration in the solution is as high as 30 g/l, the diamond content in the composite coating reaches its limiting value of 12–14 vol % (or 6.4–7.2 wt %). The optimum ultradisperse diamond concentration was found to be 17 g/l in the baths and 10.5 vol % (or 5.6 wt %) in the composite coating. At these concentrations, the coatings with the maximum microhardness and lowest brittleness are obtained.
TL;DR: The microhardness and structure of composite chromium coatings modified by dispersed CeO2 and ultradispersed diamond (UDD), as well as the granulometric UDD distribution were investigated as discussed by the authors.
Abstract: The microhardness and structure of composite chromium coatings modified by dispersed CeO2 and ultradispersed diamond (UDD), as well as the granulometric UDD distribution (both in the coatings and the bath) were investigated The presence of the particles in the coatings reduced the number of microcracks and enhanced the microhardness Passing from the chromium to the composite coatings makes the microhardness measured on the microsections and the specimen surface converge Despite the uniform distribution of the particles in the coatings, nonuniform distribution of their sizes is satisfactorily described by a lognormal distribution function A selective deposition of nano-size particles (with the most probable radius of UDD particles of 204 nm) was found out, although dynamic aggregates found in the solution have the most probable radius of 4530 nm This is possibly associated with their disaggregation near the electrode and the inclusion of the finer particles into the coating
TL;DR: In this paper, a trained neural network uniquely determines the characteristic potentials of corrosion system (the free-corrosion, passivation, and repassivation potentials) from the data on the chemical composition of corrosive medium and, based on these potentials, predicts the type of corrosion: active dissolution, passivity, or passivity with probable pitting.
Abstract: The method of neural-network analysis of experimental data is applied to the corrosion system for the first time. The neural-network simulation enables one to predict adequately the response of steel 3-chloride-containing solution system to the external effects: the variations in the pH value and in the concentration of chloride ions. Trained neural network uniquely determines the characteristic potentials of corrosion system (the free-corrosion, passivation, and repassivation potentials) from the data on the chemical composition of corrosive medium and, based on these potentials, predicts the type of corrosion: active dissolution, passivity, or passivity with probable pitting.
TL;DR: In this paper, the corrosion and electrochemical behavior of carbon steels in standard 05% chloride electrolytes acidified with CH3COOH and saturated with H2S was studied.
Abstract: The corrosion and electrochemical behavior of carbon steels in standard 05% chloride electrolytes acidified with CH3COOH and saturated with H2S was studied The possibility of protecting steels with quaternary ammonium salts (QASs) obtained by reactions of secondary and tertiary amines with benzyl chloride was investigated It was found that the protective properties of QASs depend on their chemical structures and can be expressed, to a first approximation, in terms of the Linear Gibbs Energy Relation with the use of the hydrophobic f constants and Taft σ*-constants of the substituents The presence of hydrophobic and electron-accepting substituents was found to enhance the protective properties of the inhibitors
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this paper, the authors applied boron diffusion coatings to die steels, as well as the microhardness, microbrittleness and wear resistance of the steels with the coatings.
Abstract: Applying boron, boron-copper, and boron-nickel diffusion coatings to die steels, as well as the microhardness, microbrittleness and wear resistance of the steels with the coatings are considered.
TL;DR: In this article, the effect of electric discharges on the surface structure of oxide plazma-electrolitic structures at anodically polarized aluminum alloys has been investigated.
Abstract: Changes in the temperature and concentration of the aqueous tetraborate electrolyte, particularly, its transition from true to supersaturated solution range affect the voltage at the electrodes, the elemental and phase composition and surface structure of oxide layers formed at anodically polarized aluminum alloys under the effect of electric discharges. The results are of interest as regards controlling the characteristics of oxide plazma-electrolitic structures at valve metals.
TL;DR: In this paper, a functional dependence of the calculated adiabatic ionization potentials of the clusters on the number of water molecules in them is derived, which provides a theoretical estimate of the photoionization threshold of ice.
Abstract: The possibilities of modern quantum chemical calculations in estimating the physicochemical characteristics of condensed phase specimens, when an increase in the number of particles does not lead to principal changes in the electronic structure, are demonstrated by an example of water, which is the most important solvent in actual corrosion-electrochemical processes. Stationary quantum chemical calculations of (H2O) n water clusters comprising up to 12 molecules and their cations showed that ionization induces the formation of OH and H3O+ fragments. Based on the analysis of the electron density distribution in the systems, a functional dependence of the calculated adiabatic ionization potentials of the clusters on the number of water molecules in them is derived. Extrapolation of this dependence to n → ∞ provides a theoretical estimate of the photoionization threshold of ice.
TL;DR: In this article, the electrochemical dissolution of freshly formed surface (FFS) of iron and nickel are similar as a whole, but exhibit a number of distinctions, such as a mean fraction of transferred charge in the complex of nickel (0.8) is significantly higher than that of iron(0.5).
Abstract: Regularities of the electrochemical dissolution of freshly formed surface (FFS) of iron and nickel are similar as a whole, but exhibit a number of distinctions. At an oxidation stage Me0-Me+, a water molecule chemisorbs to form a surface complex with charge transfer; however, a mean fraction of transferred charge in the complex of nickel (0.8) is significantly higher than that of iron (0.5). In weakly acid sulfate solutions (pH 1.7–3.2), the iron FFS dissolution is predominantly inhibited by hydrogen atoms formed by the discharge of hydroxonium ions and adsorbed at the dissolution centers. On nickel at pH > 2.7, the inhibition is caused by the formation of adsorbed oxygen corresponding to more positive potentials in a range of active nickel dissolution.
TL;DR: In this article, the effects of 2-substituted 5(6)-nitrobenzoimidazoles on the dissolution of copper and zinc in phosphate electrolytes were studied.
Abstract: Effects of the concentration and chemical structures of 2-substituted 5(6)-nitrobenzoimidazoles (5(6)-NO2-2-R-BIs) on the dissolution of copper and zinc in phosphate electrolytes were studied. Introduction of the nitro group into benzoimidazole derivatives was found to make them more effective for copper but less effective for zinc; this is due to an increased degree of dissociation of the nitro derivatives and the possibility of ionic bonding in their complexes. The protective effects of 5(6)-NO2-2-R-BIs on copper and zinc depend on their chemical structures and are accurately described by the equation log γ = α ± ρσ1. The sign and magnitude of ρ indicate that electron-withdrawing substituents in 5(6)-NO2-2-R-BIs enhance the protection of copper, while electron-donating ones enhance the protection of zinc; this is due to different abilities of these metals to form σ-and π-bonds in their complexes.
TL;DR: In this article, the authors focus on the formation of thin protective layers at metals, which could be successfully used for corrosion control, and restrict their consideration to conversion coatings (CCs) with a thickness ≤ 5 μm.
Abstract: The formation of thin protective layers at metals, which could be successfully used for corrosion control, has long been the focus of attention for physical chemists. Those layers are formed either during the adsorption of corrosion inhibitors (CTs) or in reactions of the cations of the metal to be protected with some components of the medium. The latter case involves not only nanosized layers formed by CIs but also thick conversion (oxide, phosphate, etc.) coatings. Let us restrict our consideration to conversion coatings (CCs) with a thickness δ of ≤5 μm. Apparently, it is methods designed to form thin and ultrathin protective layers that will be in the best demand by the technologies of the XXI century. We will consider only a few important problems that physical chemists face with when studying the possibilities of the protection of metals from corrosion.
TL;DR: In this paper, the role of the cementite phase in the passivation of iron-carbon alloys containing a pearlitic constituent is investigated, as well as the possibility of the passive layer breakdown at the boundary between the ferritic and cementite phases.
Abstract: Anodic dissolution and passivation of iron-carbon alloys containing a pearlitic constituent are investigated. The role of the cementite phase in the passivation, as well as the possibility of the passive layer breakdown at the boundary between the ferritic and cementite phases, is shown.
TL;DR: In this paper, the Gibbs surface energy of Ni-Cr alloys is taken into account, and the adsorption of an alloy component with the smaller surface energy, namely, nickel, at the alloy-oxide film interface boundary shifts the dynamic equilibrium between the alloy and oxide-film components toward the formation of NiO.
Abstract: In calculations, not only the Gibbs formation energy of nickel and chromium oxides and thermodynamic activities of the alloy components, but also the Gibbs surface energy of a Ni-Cr alloy is taken into account. The method is based on the adsorption model of the alloy oxidation, according to which the adsorption of an alloy component with the smaller surface energy, namely, nickel, at the alloy-oxide film interface boundary shifts the dynamic equilibrium between the alloy and oxide-film components toward the formation of NiO. For the oxidation of Ni-Cr alloys, which are solid solutions with an fcc lattice, at 1123 to 1473 K, concentration boundaries of the chromium content in the alloy are calculated for the case of the prevailing formation of Cr2O3 oxide, which determines the high heat resistance of Ni-Cr alloys.
TL;DR: Bismuth electrodeposition from baths containing bismuth nitrate, trilon B (disodium ethylenediaminetetraacetate Na2H2Edta), and sulfosalicylic acid H3SSA was studied with various ratios of bath components.
Abstract: Bismuth electrodeposition from baths containing bismuth nitrate, trilon B (disodium ethylenediaminetetraacetate Na2H2Edta), and sulfosalicylic acid H3SSA was studied with various ratios of the bath components. Adding H3SSA to the bath made the deposit become semibright and its current efficiency enhance.
TL;DR: In this article, a correlation between the polar properties of substituents R in an additive molecule and the nature of adsorbed and reduced species was found and analyzed, and it was demonstrated that an increase in the electron-donating and electron-withdrawing properties of R stimulates complexation between the metal and the additive in the surface layer, which makes the adsored layer more permeable and accelerates the electroreduction of metal ions.
Abstract: A correlation between the polar properties of substituents R in an additive molecule (with benzohydrazide derivatives as examples) and the nature of adsorbed and reduced species was found and analyzed. It was demonstrated that an increase in the electron-donating and electron-withdrawing properties of R stimulates complexation between the metal and the additive in the surface layer, which makes the adsorbed layer more permeable and accelerates the electroreduction of metal ions.
TL;DR: Amorphous phosphating of aluminum and its alloys AДH, Д1, and Д16 is studied in this paper, where it is found that uniform coatings are deposited at pH 4.5 at a temperature of 50°C from the solution containing MoO 4, V 2− promoting ions.
Abstract: Amorphous phosphating of aluminum and its alloys AДH, Д1, and Д16 is studied. It is found that uniform coatings are deposited at pH 4.5 at a temperature of 50°C from the solution containing MoO
4
2−
promoting ions. By using the x-ray photoelectron spectroscopy, it is shown that phosphates of aluminum and Mo(IV, V) are the predominant components of phosphate coating. By the “thin layer” method, it is found that, in the near-surface layer, alkalization of solution takes place depending on the initial pH value. The dependence pHdep = pHin ± 0.3 is linear. Phosphate coatings, which are deposited in the solution pretreated with magnetic field (MF), differ in their properties from the coatings obtained by the conventional procedure. MF can increase or decrease the corrosion resistance of phosphate coating depending on the aluminum alloy.
TL;DR: In this paper, the properties of the P-E applied structures formed under power-drop conditions are studied as functions of the potassium hexafluorozirconate bath temperature (20-70°C) and initial voltage (300-500 V).
Abstract: Some data on zirconium-containing layers plasma-electrochemically (P-E) applied to A7 aluminum alloy (obtained by using x-ray spectral and diffraction analyses, electron microscopy, as well as measuring their thickness and visible light reflection) are discussed. The properties of the P-E applied structures formed under power-drop conditions are studied as functions of the potassium hexafluorozirconate bath temperature (20–70°C) and initial voltage (300–500 V).