A. I. Marshakov

Interpretation of the Impedance Comprising Negative Capacitance and Constant Phase Elements on Iron Electrode in Weakly Acidic Media

The negative low-frequency capacitance that appears in interpretations of impedance of the iron electrode in weakly acidic solutions is shown to arise in the case of interaction of two consecutive nonequilibrium flows that constitute a two-stage anodic faradaic process of intermediate adsorption in the prepassivation potential range. The low-frequency capacitance is negative throughout a potential range where the logarithm of rate constant vs. potential (logk vs. E) dependence has the higher slope for the limiting stage. The low-frequency capacitance becomes positive at higher anodic potentials and for the other limiting stage.

Iron hydrogenation under atmospheric corrosion. Studies using a scanning vibrating microscope

A scanning vibrating capacitor (SVC, Kelvin probe) is used to study hydrogenation of iron and steel under the conditions of atmospheric corrosion. It is shown that hydrogen that forms in the course of corrosion or under cathodic polarization diffuses through the membrane and interacts with its opposite side, causing a decrease in the surface Volta potential. It is proposed that atomic hydrogen reduces Fe3+ ions in the passive film. It is shown that the SVC technique is informative for registration of local regions of hydrogenated metal at very low hydrogen flow into steel.

Effect of corrosion medium composition on rate of crack growth in X70 pipeline steel

The growth rates of corrosion cracks in X70 pipeline steel are determined in weakly acidic (pH 5.5) buffer solution with additives of a number of compounds that are a part of the soil electrolyte or are steel corrosion inhibitors. It is shown that the effect of components of electrolyte on the rate of crack growth agrees fairly well with their stimulating or inhibiting effect on the anodic dissolution of iron. The rates of hydrogen permeation into steel are measured and the effect of hydrogen absorbed by the metal on the anodic process in the studied corrosion media is considered.

Effect of Atomic Hydrogen on the Anodic Dissolution of Iron in a Weakly Acidic Sulfate Electrolyte

Using a membrane electrode, atomic hydrogen is shown to decelerate the dissolution of iron in sulfate and sulfate-citrate electrolytes (pH 5.5) in a potential range of the active metal dissolution and accelerates the process at the prepassivation potentials. Impedance spectra of iron at a controlled degree of surface coverage with hydrogen atoms are recorded. Rate constants of elementary stages of the anodic process are calculated and the reaction scheme of the iron dissolution in sulfate environments is made more accurate.

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.

Effect of cathodic polarization on the corrosion cracking rate in pipe steels

Cathodic polarization can both inhibit and promote the growth of corrosion cracks in pipe steels. The promoting effect indicates that corrosion cracking follows the mechanism of hydrogen embrittlement. The critical current of hydrogen penetration across a steel membrane can serve as a criterion for the risk of embrittlement. Critical currents of hydrogen penetration for 14Γ2CAΦ and X70 steels were determined.

The effect of atomic hydrogen on the kinetics of iron passivation in neutral solutions

Current-time dependences are recorded on iron in borate buffer (pH 7.4 and 6.7) and its mixture with NS4 solution (pH 6.7) at the potentials of passivity, active-passive transition, and prepassivation of iron. Hydrogenation of the metal is found to accelerate the dissolution of iron in steady passive state, produce no effect on the growth of a barrier layer, and prevent the formation of a primary passivating film. Atomic hydrogen decelerates the active dissolution of iron, which determines the anodic current at the initial stage of the metal passivation.

The effect of sorbed hydrogen on the kinetics of active dissolution of iron

The effect of hydrogen adsorbed or absorbed by iron (0.009% C) on the iron dissolution is studied on a bipolar electrode-membrane in 0.5 M SO42− solutions (pH 1.30) by cyclic potential pulses. Expressions that allow one to calculate the hydrogen coverage on the iron surface (θ) as a function of the potential variation in a cyclic stepwise manner and also the hydrogen concentration in the near-surface metal layer (C) as a function of variations in the intensity of the diffusion flow of hydrogen atoms in the membrane are given. The method of cyclic potential pulses together with the analysis of solutions for metal ions shows that the iron dissolution rate substantially decreases as θ increases. A bipolar electrode-membrane allowed the determination of the C intervals corresponding to the inhibition of iron dissolution (at C < Cc ≈ 3 × 10−8 g-at/cm3), the activating effect of hydrogen absorbed by the metal on the anodic process (for C > Cc), and the metal destruction (for C ≫ Cc). The absorbed hydrogen is assumed to accelerate the ionization of iron due to the formation of new dissolution sites as a result of plastic deformations of the metal. Thus, the effects of two forms of sorbed hydrogen on the iron dissolution are separated.

The Effect of Sorbed Hydrogen on the Dissolution of Iron in a Thiocyanate-Containing Sulfuric Acid

With the cycling of potential step, the dissolution rate of iron is shown to decrease with an increase in the degree of its surface coverage with hydrogen atoms. With a bipolar electrode (a membrane), an increase in the concentration of hydrogen in the metal phase was found to decelerate the anodic dissolution of iron in a base sulfate electrolyte and accelerate it in the presence of thiocyanate ions. The latter phenomenon indicates the possibility of activating the ionization of iron with the hydrogen dissolved in it. The rate constants of individual stages of the cathodic evolution of hydrogen are calculated.

Comparative estimation of long-term predictions of corrosion losses for carbon steel and zinc using various models for the Russian territory

ABSTRACT Based on the results of 1-year tests at 12 sites in the Far Eastern region of Russia, priority dose–response functions (DRFs) that provide the best match with experimental data on corrosion losses for carbon steel and zinc have been selected. Long-term (up to 50 years) predictions of corrosion losses of these metals in the continental territory of Russia have been given. A comparative estimation of the mass loss predictions by priority DRFs and the power–linear model has also been given.