L. E. Tsygankova

Interrelation between Kinetics of the Hydrogen Ion Reduction on Iron and the Hydrogen Diffusion Flux into Carbon Steel in Acidic Solutions

Kinetic parameters of discharge of hydrogen ions, which depend on the nature of the slow stage in the Volmer–Tafel and Volmer–Heyrovský mechanisms, are obtained theoretically for commensurate rates of successive reactions on energetically-uniform and evenly-nonuniform surfaces. The results are compared with similar experimental parameters for the Armco iron in the system C2H4(OH)2–H2O + HCl. Upon adding 2–10 wt % H2O into C2H4(OH)2, the slow discharge stage gives way to the Tafel reaction if the hydrogen ion adsorption obeys the Temkin isotherm. Upon going to purely aqueous solutions, the discharge process becomes the limiting stage again. A change in the hydrogen diffusion flux through a steel membrane from these mixed solvents does not correlate with the nature of the stage that controls the cathodic reduction of hydrogen ions.

Effect of Sodium Hydroarsenate on the Kinetics of Reduction of Hydrogen Ions at Iron and on the Hydrogen Diffusion through a Steel Membrane from Aqueous and Ethylene Glycol Solutions of Hydrochloric Acid

Effect of arsenic compounds H3AsO4, H2AsO4–, and HAsO42– on the hydrogen overvoltage, the slow stage of discharge of hydronium ions on the Armco iron, and the hydrogen diffusion through a steel membrane from aqueous and ethylene glycol solutions of hydrochloric acid with a constant ionic strength of unity is considered.

A Study of Hydrogen Accumulation in Multiwall Carbon Nanotubes by Electrochemical Techniques

Accumulation of electrolytic hydrogen in alkaline medium (5 M KOH) by multiwall carbon nanotubes (MWCNTs) 20–60 nm in inner diameter and 2 μm in length obtained by catalytic pyrolysis of propane/butane mixture has been studied by means of the electrochemical diffusion technique, cyclic voltammetry, and impedance spectroscopy. MWCNTs were applied on a steel membrane and were encapsulated by a 10-nm electrolytic nickel layer. Cyclic voltammograms were recorded in the range of potentials from −1.2 to +0.2 V and contained a current peak in the cathode region corresponding to hydrogen absorption by nanotubes at −0.9 V and current peak in the anode region corresponding to oxidation of absorbed hydrogen at −0.6 V. Hydrogen storage capacity of MWCNTs varies from 4.6 to 6.5% depending on the amount of nanotubes according to electrochemical diffusion data. The electrochemical impedance data correlate with the results of the above methods.

Kinetics and nature of the slow stage of cathodic hydrogen evolution on iron in aqueous and water-ethylene-glycol solutions of HCl in the presence of o-fluorophenylbiguanidine

The influence of the concentration of o-fluorophenylbiguanidine (FF) (0.5–40 mM) on the kinetics of hydrogen evolution on iron in aqueous and ethylene glycol (10 wt % H2O) solutions with an electrolyte x M HCl + (1 − x) M LiCl was studied. In aqueous media, the introduction of increasing concentrations of FF led to a transition from one slow stage to other stages in a series: slow discharge → slow recombination → slow lateral diffusion → slow discharge. In ethylene glycol media, the series is formally the same, but there is no initial slow discharge and hydrogen evolution (HER) in supporting solutions is limited by chemical recombination, which shifts to slow lateral diffusion already in the presence of 0.1 mM FF. In aqueous solutions, this change in the nature of the rate-limiting stage requires a 50-fold increase in the FF concentration. Finally, at a certain FF concentration, HER occurs under the conditions of slow discharge.

Effect of Cathodic Polarization of a Steel Membrane and the Acidity of Alcohol Solutions of Hydrochloric Acid on the Balance between Rates of the Reaction of Evolution of Hydrogen and Its Solid-Phase Diffusion

The effect of cathodic polarization of the entrance side of a steel membrane and the concentration of hydrochloric acid (0.99–0.01 M) on the balance between rates of the reaction of evolution of hydrogen and its diffusion through steel (ρ) is studied in hydrochloric-acid solutions of ethanol and ethylene glycol with a constant ionic strength equal to unity. It is demonstrated that ρ lowers down with a shift of the potential of the polarization side of the membrane in the negative direction and increases with diminishing concentration of hydrochloric acid. The results are interpreted with allowance made for the surface coverage by two forms of adsorbed hydrogen, namely, a raised form and a subsurface form.

Effects of pH and a hydrogenation stimulator on rate constants of cathodic evolution of hydrogen and its diffusion into steel in acid sulfate solutions

From steady-state and non-steady-state polarization measurements, kinetics parameters for the hydrogen evolution reaction at carbon steel in acid sulfate solutions in the absence and in the presence of KCNS are calculated. Based on the results obtained by an electrochemical diffusion method and using the Iyer-Pickering-Zamanzadeh analysis, apparent rate constants for the principal stages of the hydrogen evolution reaction are calculated.

Effect of Anodic Polarization on the Hydrogen Diffusion through a Steel Membrane in Ethylene Glycol Solutions

Diffusion of hydrogen through a steel membrane from ethylene glycol solutions of HCl containing 0.1–10 wt % H2O is studied. The effect of the nature of discharging proton, hydrogen ion concentration, and anodic polarization on the process is considered. Kinetic parameters of cathodic reduction of proton donors on the Armco iron under similar experimental conditions are obtained.

Accumulation of Electrolytic Hydrogen by Carbon Nanotubes

The accumulation of electrolytic hydrogen synthesized in a 5 M KOH solution by double- and triple-walled carbon nanotubes (CNTs) deposited on a steel membrane and encapsulated by an electrolytic iron layer of the thickness of 10 nm was studied. CNTs were synthesized by catalytic pyrolysis of methane and are characterized by an inner diameter of 2–4 nm, a length of up to 10 μm and more, and a specific surface area of 600–800 m2 g–1. The studies were performed by electrochemical diffusion, cyclic voltamperometry, and electrochemical-impedance spectroscopy. It has been shown that the hydrogen-storage capacity in CNTs varies in the range of 4–25% depending on the content of nanotubes in the composite.

ESTIMATION OF THE SELECTIVITY OF THE ACTIVE CENTERS OF SORBENTS DURING SORPTION OF ECOTOXICANTS FROM MULTICOMPONENT SOLUTIONS

A method for assessing the selectivity of active centers upon sorption of sorbates from multicomponent solutions containing three or more pollutants is proposed. The method is based on comparison of the values of specific sorbent capacity for each of the sorbates when they are extracted from single-pollutant (one pollutant) and multipollutant (all contaminants simultaneously) solutions. Both stationary and flowing solutions to be studied contained close and significantly different initial concentrations of eco-pollutants. At the first stage, stationary solutions contained a single pollutant (then all three at the same time) at a given equal (close) initial concentration, the sorbent mass in them being fixed strictly. At a given moment of time ф i, the capacity of the sorbent Qi for each sorbate is estimated. Then the same experiment is carried out with the solutions containing all three pollutants simultaneously. If Qi ( ф i = const) does not depend on the presence of other pollutants, then the selectivity of the active centers of the sorbent takes place. If it decreases with the introduction of other pollutants, the selectivity is absent. At the second stage, the same experiment is carried out in the flow solutions, and at the third stage at the concentration of one the sorbate (10 – 100 times) lower than that of others (flow media). In all cases, the value Qi of each i-th sorbate is also estimated and the same theoretical analysis is carried out. Results of sorption of metal cations (Me (II)) (iron group) on glauconite at practically identical their initial concentrations and Ni (II) from media with high (more than 100-fold) content of hardness cations (Ca (II) and Mg (II)) are presented as an example. The high selectivity of the active sorbent centers is shown.

Universalism of Hydrogen Sulfide and Carbon Dioxide Corrosion Inhibitors in Conditions of Oil Production and Processing

Qualitative criteria for the universalism of hydrogen sulfide and carbon dioxide corrosion inhibitors and their quantitative indices for the corrosion of carbon steel are proposed. They include the maximum value of the total corrosion rate in the presence of H2S and CO2 and with simultaneous limitation of the concentration of the inhibitors themselves. The criteria define a minimum reduction in hydrogenation of steel, suppression of hydrogen diffusion into the metal, contain requirements for the bactericidal ability of inhibitors by limiting the number of cells of sulfate-reducing bacteria and producing hydrogen sulfide, and the requirements for their biodegradability. It is shown that a number of domestic inhibitors of hydrogen sulfide and carbon dioxide corrosion of the new generation of the INKORGAZ series fully satisfy the proposed criteria for universalism.