D. B. Vershok

Features of formation of magnetite coatings on low-carbon steel in hot nitrate solutions

The process of anticorrosion magnetite coating (MC) formation on low-carbon steel is studied in alkali-free nitrate converting media at the temperatures of 70–98°C reduced as compared to those used (130–145°C) in standard technologies of steel bluing: formation of such coatings in alkaline nitrate solutions. Alongside with the conventional corrosion-electrochemical methods of analysis of the formed MCs, the regularities of the MC surface reliefs were studied using the method of atomic force microscopy combined with the technique of flicker-noise spectroscopy (FNS) for processing digitized images and obtaining the parameters of the MC surface structure in different nanometer ranges. It was shown that it is necessary to introduce additives of metal nitrates with a low cation radius into the ammonium nitrate converting solution to obtain MCs with a high corrosion stability at the first stage of MC formation and the final stage must consist in the further “passivation” of MCs: MC treatment by aqueous solutions based on nontoxic carboxylates. According to the FNS analysis of the surface structure of the formed MCs, a significant decrease of the FNS “point” factor, an indicator of MC corrosion instability, occurred during the final treatment. On this basis, one could characterize quantitatively the results of accelerated corrosion tests: no steel corrosion occurred on the thus formed coatings for 42 days under standard severe conditions: 100% relative humidity and daily “showering”. The performed study reveals fundamental possibilities for solving the problems of standardization of the anticorrosion coating surface based on the analysis of their surface profile in the nanometer range.

Impedance of Magnetite-Coated Steel Electrodes

Steel electrodes coated with magnetite of different defectiveness are studied by the electrochemical impedance method. In a borate buffer, the impedance is adequately described by an equivalent circuit for a passive steel electrode. The magnetite coating defectiveness can be evaluated from the frequency peak shift in a Bode diagram.

Superhydrophobization of low-carbon steel with conversion coatings

Hydrophobization of a surface by fluorosilanes is proposed for protection of low-carbon steel with conversion coatings from atmospheric corrosion. The effect of the heterogeneity of conversion coatings on their hydrophobicity is shown. Employment of superhydrophobization processing increases the angle of wet- ting of the surface by a water droplet up to 160° and significantly enhances the anticorrosion properties of such a composite coating.

On the formation of magnetite coatings on low-carbon steel in ammonium nitrate solution

Initial stages of the formation of magnetite coating (MC) on low-carbon steel in ammonium nitrate solution at a temperature of 98°C is studied by atomic force microscopy. Analyzing the results obtained by flicker-noise spectroscopy allows the degree of continuity and structuring of MC to be estimated. It is shown that the formation of magnetite nuclei in the course of direct electrochemical reaction may take place in the first minutes of oxidation; continuous coating is formed in 10–15 min.

Parameterization of the Magnetite Coating Surfaces on Low-Carbon Steel with the Use of Atomic Force Microscopy Data

The atomic force microscopy (AFM) technique is used to obtain information on the dynamic behavior of the magnetite coating (MC) formed on a steel 3 (St3) sample by chemical oxidation in a solution of ammonium nitrate. Digitized AFM data are the sets of profiles of chaotic roughness obtained via a sensing probe scanning over the surface fragment under study. The flicker noise spectroscopy (FNS) technique is used to analyze AFM images and to select parameters adapted to MC state characterization at the initial stages of formation. The FNS parameters introduced to characterize coating surfaces are calculated from spatial power spectra and transient structure functions. These parameters are considered to be the correlation lengths for different-type irregularities (jumps and spikes). Additionally, dimensionless parameters are introduced to characterize the loss of correlation in a series of irregularities when spatial intervals are substantially less than the correlation lengths. The performed FNS parameterization enabled us to obtain information on the state of the initial surface of St3 samples and to reveal the structural features intrinsic to the surface of MCs formed after different periods of oxidation. This information determines correlations between the elements of the MC structure and characterizes the properties of its microirregularities arising at different stages of coating formation.

Two-step oxidation of steel in nitrate solutions

The possibility of increasing the thickness of a magnetite coating (MC) and its heterogeneity due to successive oxidation of low-carbon steel in two bathes based on ammonium nitrate solutions has been shown. Results are shown of a comparative corrosion test of steel with an MC obtained during single- or two-step oxidation in nitrate solutions, with further passivation by the IFKhAN-39U composition, which show the advantages of oxidation in two bathes.

The influence of zinc cations on steel oxidation in nitrate solutions

AbstractThe influence of zinc nitrate additives on the protective properties of the magnetite coating (MC) obtained by the oxidation of low-carbon steel in the nitrate solution at temperatures of 96–98°C has been studied by physical, electrochemical, and corrosion methods. It has been shown that, under these conditions, iron zinc spinel ZnFeO4, which is introduced into an MC, can be formed. Low concentrations (

IMPROVEMENT OF THE PROTECTIVE PROPERTIES OF MAGNETITE COATINGS BY METAL PHOSPHONATES

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