Investigations of the hydrogen evolution kinetics and hydrogen absorption by iron electrodes during cathodic polarization

The kinetics of the electrochemical reduction of hydrogen ions or water molecules on iron electrodes have been investigated using the electropermeation technique. The variation of permeation current density and cathodic potential with constant cathodic current density has been measured in various solutions, without or with promoters. The hydrogen activity on the cathodic side of the iron membranes was calculated from the H-permeation current. The exchange current densities of the three partial reactions of the cathodic hydrogen evolution were calculated from the obtained experimental data. In 0.1N H₂SO₄ without added promoters the chemical Tafel recombination predominates up to high cathodic current densities whereas in 0.1N NaOH or nearly neutral solutions without added promoters the electrochemical Heyrovsky recombination predominates already at comparatively low cathodic current densities. This is mainly due to the different exchange, current densities of the electrochemical recombination reaction with hydrogen ions or with water molecules. The promoter used enhances the hydrogenation of iron by inhibiting the recombination reactions stronger than the Volmer reaction.     

The hydrogen evolution reaction on iron corroded in dilute and very dilute solutions of sulfuric acid

Permeation transients for hydrogen, generated by corrosion of iron in dilute solutions of sulfuric acid, were recorded with an improved electrochemical permeation apparatus.The mechanism of the hydrogen evolution reactions is coupled discharge hydrogen recombination for all methods of hydrogen generation, low current anodic polarization, cathodic polarization and corrosion.The experimental hydrogen transient was compared with that predicted theoretically.It is concluded that electrochemical hydrogen permeation is a sensitive tool for investigating processes on metal surfaces which are of engineering importance.     

On the participation of hydrogen sulfide in the cathodic reaction on iron

The immediate cathodic reduction of H₂S molecules on iron is substantiated by the use of voltammetric curves. Phase films of iron sulfide and hydroxide are formed on iron upon reaching the limiting current of hydrogen ions.     

Chemische und elektrochemische Reaktionen von Eisensulfid und Mangansulfid in sauren und neutralen Lösungen

Chemical and electrochemical reactions of iron sulfide and manganese sulfide in acid and neutral solutions The reactions which occur upon corrosion of massive iron sulfide and manganese specimens in perchloric acid and in neutral sodium chloride solution were elucidated by measurements of current-potential curves and by coulometric and analytical investigations on the processes. In acids the sulfides are dissolved by prevailing chemical reaction under evolution of H₂S. Upon applying anodic overpotentials electrochemical reactions occur simultaneously, however, with such low velocity that the contribution to corrosion of the sulfides is insignificant. Upon applying cathodic overpotentials some hydrogen discharge is observed on iron sulfide but not on manganese sulfide. In 3% sodium chloride solution both sulfides corrode very slowly upon anodic polarization, forming elementary sulfur according to MeS = Me²⁺ + S + 2e^? (Me = Fe or Mn). At high anodic potentials additional oxidation reactions occur in which three-valent iron and tetravalent manganese ions as well as sulfite and sulfate ions are formed. Iron sulfide and manganese sulfide inclusions can he isolated from steels only by electrochemical dissolution in neutral or weakly basic electrolytes, the potential during electrolysis must not be more positive than the corrosion potential of the sulfides.     

Probing into the effects of a magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate based on the fundamental electrochemistry kinetics

The effects of an applied magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate have been investigated by electrochemical measurements. Open circuit potentials, cathodic and anodic polarisation curves, values of polarisation resistance were measured in the presence or absence of a 0.4 T horizontal magnetic field (HMF). A potentiostatic polarisation plus magnetic field perturbation technique was used to study the effect of the magnetic field on open circuit corrosion. Cathodic reaction rates at open circuit potentials for iron in sulphuric acid solutions containing dichromate ions are controlled by both the electron-transfer process and the diffusion process. A magnetic field made the open circuit potential move in the positive direction, and changes of the open circuit potentials due to the magnetic field increase with increasing dichromate concentration. When iron was potentiostatically polarised at open circuit potentials in the absence of a magnetic field, a cathodic current was observed after a magnetic field was imposed. Such cathodic currents induced by the magnetic field increases with increasing dichromate concentration. The positive shifts of open circuit potential, the decrease of polarisation resistance, and the occurrence of cathodic currents induced by the magnetic field are caused by the accelerating effect of magnetic field on the cathodic diffusion process. Measured current densities showed lower, equal, or higher values in the presence of the magnetic field than those in the absence of a magnetic field at certain anodic potentials. This effect of the magnetic field is related to the contribution of the cathodic and anodic reactions to the measured current and the types of rate-determining steps for each reaction at certain potentials. The applied magnetic field significantly decreased the polarisation resistance. The experimental results in this paper are formulated based on the fundamental electrochemistry kinetics after introducing a coefficient term of the magnetic field effect on the mass transfer process of reactive ions.     

Study of the electrochemical permeation of hydrogen in iron

Hydrogen permeation through iron membranes of different thicknesses was studied by the electrochemical permeation technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C.The measured build-up and decay permeation current transient had been examined.The experimental results revealed that the diffusion apparently increases with decreasing membrane thickness. This result suggests that the hydrogen transport through membrane was mainly governed by hydrogen trapping at the trap sites present at the grain boundaries.The influence of the passive layer on the hydrogen permeation and its influence on the evaluation of diffusion and trapping characteristics were discussed.     

Determining true rate constants of hydrogen evolution and solid-phase diffusion at adsorption of inhibitor

The adsorption of benzalkonium chloride on a surface of St3 steel in 0.1 N HCl + 0.9 N KCl and 0.9 N HCl + 0.1 N KCl solutions is studied using impedance spectroscopy. Taking into account the surface coverage of the electrode with the inhibitor, the true rate constants of the main stages of the cathodic hydrogen evolution and solid-phase diffusion of hydrogen, as well as the surface coverage with hydrogen in the solutions studied, are calculated.     

Effect of residual stresses on hydrogen permeation in iron

The effect of residual stresses on electrochemical permeation in iron membrane was investigated. Four thermal and mechanical treatments were chosen to obtain different surface states in relation to the residual stresses.Residual stresses were determined by X-ray diffraction (XRD) using the Macherauch and Müller method. The results were completed by the microhardness measurements. For all iron membranes, compressive residual stresses were obtained.Electrochemical permeation experiments using a Devanathan and Stachurski cell were employed to determine the hydrogen permeation behaviour of the various iron membranes. The latter was charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C. The experimental results revealed that hydrogen permeation rate increases with increasing residual stresses introduced in iron membranes.     

The hydrogen permeation investigation of API X56 steel in sea mud

It was found that the corrosion rate of steel in the sea mud with sulfate‐reducing bacteria (SRB) could be as high as 10 times of that in the sea mud without SRB. And the hydrogen permeation reaction would occur when metals were corroded. So it is necessary to investigate the effect of living SRB on hydrogen permeation in the sea mud. Cathodic potential was often added to metals in order to protect them. But hydrogen permeation could be affected by the cathodic potential. So it is also necessary to study the effect of cathodic potential on hydrogen permeation. In this paper, the hydrogen permeation actions of API X56 steel in the sea mud with and without SRB at corrosion and cathodic potential were studied with an improved Devanathan‐Stachurski's electrolytic cell. Experimental results showed that during the growth of SRB, the current density curve of hydrogen permeation was accordant with the growth curve of SRB. But the hydrogen permeation current density of API X56 steel hardly changed in the sterilized sea mud. Compared with the hydrogen permeation current density of API X56 steel in the sterilized sea mud, the hydrogen permeation of API X56 steel in the sea mud could be accelerated by living SRB. Experimental results also showed that the hydrogen permeation current density increased rapidly when the cathodic potential was added to the three‐electrode system of the cathodic cell, and then the hydrogen permeation current density could obtain a stable value slowly. So the cathodic potential added to the cathodic cell could accelerate hydrogen permeation.     

Elektrochemische Untersuchungen zum kathodischen Korrosionsschutz mit Unterbrecherpotentiostaten

Electrochemical investigations into cathodic corrosion protection using an interruption-potentiostat Stationary and instationary electrochemical investigations were carried out on iron in the cathodic and on platinum coated titanium in the anodic region for further developments on the field of the potentiostatic cathodic corrosion protection. Using the results obtained an interruption-potentiostat was developed, which allows to avoid the normally used reference-electrode at the potentiostatic cathodic protection. This becomes possible by using this interruption-potentiostat and an inert anode, whereby the flowing current is interrupted periodically for a short time. In the cut off time the anode, which is normally used as counter electrode, is now after a delay of about 30 μs the reference electrode to measure the existing potential E_ist of the iron which has to be protected. This potential will be compared to the potential E_soll adjusted at the potentiostat and the difference E_ist – E_soll is used for the regulation of the protection current flowing during the switch on time. The investigations carried out for some time with such an interruption-potentiostat show that iron can be protected cathodically in this way without the undesired generation of hydrogen.     

Inhibitory effects of manganeous,cadmium and zinc ions on hydrogen evolution reaction and corrosion of iron in sulphuric acid solutions

The presence of metal ions (Cd²⁺, Mn²⁺, Zn²⁺), more electronegative than the cathodic potential for the hydrogen evolution reaction on iron in a 0.25M H₂SO₄ solution, inhibits the hydrogen evolution reaction and corrosion of iron. This effect has been explained as the under-potential deposition of the adatoms of these metals on iron.     

In situ monitoring the effects of a magnetic field on the open-circuit corrosion states of iron in acidic and neutral solutions

The effects of a 0.4 T horizontal magnetic field (HMF) on the open-circuit corrosion states of iron in static aqueous solutions are studied by in situ monitoring the responses of two electrochemical parameters to the applied magnetic field, i.e. the open-circuit potential (OCP) and the current under potentiostatic polarization. The applied magnetic field makes the OCP shift in the noble direction. Withdrawing the magnetic field causes a negative shift of the OCP in acidic solutions, but it does not cause any significant change of OCP in neutral solutions. Imposing a magnetic field induces a cathodic current for iron that was previously potentiostatically polarized at the OCP without magnetic field. Withdrawing the magnetic field induces an anodic current for iron that was previously potentiostatically polarized at the OCP with the magnetic field. The magnetic field effect is more significant in the acid solutions than in the salt solutions. The magnetic field effects on the oxygen reduction and on the activation-controlled iron dissolution reaction are found to be insignificant. The magnetic field effect on the hydrogen reduction reaction on iron in acidic solutions is demonstrated. Results show the possibility that a magnetic field would affect the hydrogen evolution by enhancing the electron-transfer process that has been categorized in the classical electrochemistry kinetics to be the rate-determining process. The memory effect of the magnetic field on the electrochemical reaction is identified and discussed.     

Measurement of steady-state hydrogen electrode reactions on Alloys 600 and 690 tubes

The steady-state polarization measurements for HER and HOR were carried out in order to obtain the effects of hydrogen pressure, solution pH, and temperature on the current densities of Alloys 600 and 690, respectively. Optimization was performed to obtain the electrokinetic parameters of HER and HOR on Alloys 600 and 690 such as forward and reverse transfer coefficients and equilibrium corrosion densities. From the optimization process, the activation energies, E_ac, of both hydrogen reactions on the surfaces of the Alloys 600 and 690 tubes were obtained as 30.5 kJ/mole on the surface of Alloy 600 tube and 35.6 kJ/mole on Alloy 690 tube. Furthermore, the equilibrium exchange current densities of hydrogen electrode reaction, i₀(H₂), on the surface of the Alloys 600 and 690, respectively, were proposed as functions of hydrogen pressure, solution pH, and temperatures.     

Mild steel corrosion modelling in presence of hydrogen sulphide in aqueous solutions

Abstract

Corrosion of mild steel in aqueous solutions containing hydrogen sulphide was modelled under the condition that an iron sulphide film was formed on the steel surface. In the present model, the iron sulphide forms on the steel surface as a result of a solid state reaction between iron and hydrogen sulphide which has several steps. First a very thin film of iron sulphide nucleates on the steel surface. Then, due to further growth of the initial thin layer, a more porous layer of iron sulphide forms on the initial film. In the present model, it is assumed that mass transfer through the thin iron sulphide layer (i.e. adjacent to the steel substrate) controls the corrosion rate of steel in H₂S aqueous solutions, and as a result electrochemical reactions were not considered. The model was verified against the published experimental data and effects of some parameters such as hydrogen sulphide partial pressure were investigated. The results show that increase in partial pressure of hydrogen sulphide leads to an increase in the corrosion rate of mild steel at the primary stages of the reaction, but as a consequence of formation of iron sulphide scales on the steel surface, it drops with respect to time.     

A study on cobalt electrodeposition onto a carbon steel electrode

Abstract

The electrodeposition of cobalt on to a carbon steel working electrode was studied through the comparison between theoretical and experimental polarisation curves. The former was obtained using the Butler–Volmer equation with electrochemical parameters, such as Tafel slope values, exchange current densities, cathodic limit current densities and equilibrium potential values. The following results were obtained: the anodic region refers to the iron oxidation with a Tafel slope of about 0·055 V decade^?1, which is near the theoretical value (0·059 V decade^?1); the experimental cathodic region represents the cobalt and hydrogen ion reduction; the limiting current density (?1 × 10^?3 to ?1 × 10^?2 A cm^?2) obtained was near the calculated value, ?3·7 × 10^?3 A cm^?2.     

The influence of ion implantation on the corrosion behaviour of iron in acid solution

The influence of ion implantation on the aqueous corrosion of pure iron in IN H₂SO₄ was studied. The iron was bombarded with 5 × 10¹⁵–10¹⁷ ions.cm^?2 of Ne, Ar, Cu, Pb and Au. The current density-potential curves of the implanted samples were measured and compared with that of untreated pure iron. Ne⁺ and Cu⁺ bombardments lead to a slightly higher corrosion rate in comparison with untreated iron. Pb⁺ depressed the corrosion rate by orders of magnitude, Au⁺ enhanced it by a factor of more than ten. The effect is attributed to a reduction or an increase of the activity of the electrode surface with respect to the cathodic hydrogen evolution reaction, i.e. the ion implantation influences strongly the exchange current density of the hydrogen evolution reaction. A marked influence of the implantation on the anodic behaviour of the corroding metal could also be observed.     

Corrosion and Electrochemical Behavior of Titanium in aqueous sulfidic solutions

This paper summarizes the results of an investigation of the corrosion and electrochemical behavior, including cathodic hydrogen absorption, of titanium in acidic and alkaline sulfidic solutions. The effect of chloride and cyanide ions on the corrosion behaviour of titanium in sulfidic solutions was also studied. Titanium in acidic and alkaline sulfidic solutions exhibits a stable passive corrosion potential and negligible corrosion. Chloride and cyanide ions do not affect the corrosion behavior of titanium in sulfidic solutions. Cyanide ions under conditions of cathodic polarization tend to promote activation of titanium. Cathodic polarization at temperatures higher than 72 °C promotes hydrogen uptake in titanium and formation of titanium hydride. The rate of hydrogen uptake increases with decreasing pH and increasing temperature. Cyanide ions tend to promote the rate of hydrogen uptake, whereas chloride ions have essentially no effect.     

The effect of absorbed hydrogen on the corrosion behavior of sintered NdFeB magnet

The absorption of hydrogen by NdFeB magnet has been investigated by using the electrochemical charging technique at constant cathodic current density I_c ranging from 0 to 4 mA/cm². Open circuit potential measurements (OCP) and polarization curves were carried out to study the corrosion behavior of the charged NdFeB magnet in 0.01 mol/L NaCl solution. The results showed that hydrogen had a strong influence on the corrosion of NdFeB magnet. The open circuit potential became gradually negative due to the hydrogen incorporation into the NdFeB magnet. The corrosion resistance was reduced gradually with the increasing cathodic current density I_c. The surface structure and the morphology of the charged NdFeB magnet were examined by XRD and SEM. The results revealed that the effect of the absorbed hydrogen focused mostly on accelerating the exfoliation corrosion of Nd₂Fe₁₄B matrix grain.     

Korrosion von unlegiertem Stahl in sauerstoffreier Kohlensäurelösung

Corrosion of unalloyed steel in oxygen-free carbonic acid solution The investigation into the influence of dissolved carbon dioxide on the anodic partial reaction of iron dissolution in 0.5 M sodium sulfate solution has revealed, in agreement with data published in literature,

• 1 ) that the transfer of acid molecules to the cathode is the step controlling the rate of cathodic hydrogen evolution in oxygen-free solutions of little dissociated weak acids. The cathodic limiting current density is, consequently, a direct function of acid concentration and not of the pH value as in the case of strong acids.
• 2 ) that the anodic dissolution of iron in sulfate solution is catalyzed by carbonic acid which gives rise to a change of the dissolution mechanism, although this change is not reflected by a change of the cathodic protection potential (?0.85 V_CU/_CuSo4) which, consequently aplies to waters rich in carbonic acid, too.

     

Inhibition of the anodic dissolution of iron in alkaline solution by metal complex ions

The possible inhibiting effects of GaO₃^3?, GeO₃^2?, CrO₃^2?, and MoO₄^2? ions on anodic and cathodic reactions on iron in 5 M KOH were studied. It was shown that a concentration of these ions of 10^?3 M inhibits the anodic iron dissolution reaction 2–3 times, while no effect on the hydrogen evolution reaction was observed. The effect was explained by the underpotential deposition of adatoms of the metal complexing ions on the iron electrode.