Hydrogen evolution reaction on spheroidal graphite cast iron with different pearlite areas in sulphuric acid solutions

The rate equation of hydrogen evolution reaction of spheroidal graphite cast iron with different pearlite area has been studied in sulphuric acid solutions at 298 K. The cathodic Tafel slope of ?0·130 V/decade and the reaction order with respect to the activity of hydrogen ion of 1 are obtained by linear potential sweep technique. The rate equation of hydrogen evolution reaction does not depend on the area of pearlite. There is no difference in hydrogen evolution reaction mechanisms between pure iron and spheroidal graphite cast iron.     

Structural effects of organic compounds as corrosion inhibitors for hydrogen entry into iron in sulphuric acid

Effects of propynol, methyl-propynyl ether, N,N-dimethylpropynylamine and trimethylpropynyl ammonium cation on hydrogen entry into iron and corrosion were investigated by weight loss tests and electrochemical measurements in de-aerated 1 N sulphuric acid. Trimethylpropynyl ammonium cation gave the best inhibition for hydrogen entry. It is proposed that the inhibition of hydrogen entry by acetylenic compounds is essential to lower the π electron density by the introduction of a strong electron attracting group adjacent to the triple bond, resulting in the enhancement of adsorption by back-donation.     

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.     

Potentiostatic studies of the corrosion of grey cast iron in sulphuric acid and sodium hydroxide solutions

A potentiostatic investigation of the corrosion behaviour of two grey cast iron specimens has been performed in 2.5 M H₂SO₄ and 1.0 M NaOH solutions in the temperature range from 303 to 333 K. A similar determination was also made with both specimens in 5.0 M solutions of both HCl and HNO₃ at 303 K. The rates of corrosion at various temperatures (T) for the equilibrium, active and passive states were obtained from the corresponding values of the current densities (i) at such temperatures. Activation energies (E) of the corrosion process in each state were derived. The influence of certain sulphur and nitrogen containing compounds as inhibitors for acid or alkali corrosion of cast iron samples was also investigated at 303 K. The greatest corrosion protection was achieved with both types of cast iron in H₂SO₄ solution containing thiourea, while this substance showed only a limited protective effect in NaOH solution.     

The corrosion behaviour and hydrogen evolution reaction of Fe in non-aqueous formic acid

The corrosion of Fe in de-oxygenated non-aqueous formic acid was studied by the impedance method. It was confirmed that the cathodic reaction is a hydrogen evolution reaction (h.e.r.) and that formaldehyde is not formed. The rate-determining step (r.d.s.) of the h.e.r. is the formation of adsorbed hydrogen. The presence of adsorbed hydrogen was confirmed by the appearance of the low frequency capacitive arc obtained in the cathodic Tafel region of the impedance diagram. The inductive arc regarded as being due to the anodic dissolution of Fe was seen in the potential range between E_corr and cathodic Tafel region.     

Effect of high gradient magnetic fields on the anodic behaviour and localized corrosion of iron in sulphuric acid solutions

The influence of high gradient magnetic fields on the anodic dissolution of iron in sulphuric acid solutions and the localization of the corrosion attack is investigated by means of potentiodynamic and potentiostatic polarization experiments and subsequent surface profile analysis. A localization of the material loss is observed in every potential region of the anodic Fe dissolution except from the passive region. The impact of the magnetic field on the anodic current density and the localization of the corrosion attack are explained by the action of the Lorentz force and the magnetic field gradient force.     

Schiff bases of ethylenediamine as corrosion inhibitors of zinc in sulphuric acid

The work described here deals with the performance of ethylenediamine N,N^′-dibenzylidene, ethylenediamine N,N^′-di(p-methoxybenzylidene), ethylenediamine N,N^′-disalicylidene as corrosion inhibitors for zinc in sulphuric acid. The effect of various parameters on the efficiency of these inhibitors has been studied. Ethylenediamine N,N^′-di(p-methoxybenzylidene) and ethylenediamine N,N^′-disalicylidene give 99% protection under a variety of conditions. Activation energies in the presence and absence of inhibitors have been calculated. It appears that an efficient inhibitor is characterized by a relatively greater decrease in free energy of adsorption, relatively lower entropy of adsorption and relatively lower heat of adsorption. Galvanostatic polarisation studies indicate that these are basically cathodic inhibitors. Cathodic protection in the presence of these inhibitors has been studied. With an efficient inhibitor, cathodic protection is achieved at potentials much less negative than that required for plain acid. The difference between protective potential and corrosion potential appears to be less for an effective inhibitor. Mechanism of the action of inhibitors has been provided.     

Kinetics of hydrogen evolution reaction on iron and its diffusion through membrane from ethylene glycol solutions

The article discusses the effect of guanidine concentration on the rate of hydrogen evolution reaction (HER) on iron in ethylene glycol-water (0.1 and 50 wt. % H₂O, respectively) solutions of HCl with constant ionic strength. In an ethylene glycol environment, guanidine does not vary the rate of HER and the essence of the delayed stage, but rather increases the hydrogen diffusion rate through steel membrane. In the environment with binary solvent, containing 50 wt. % C₂H₄(OH)₂ and electrolyte of the same composition, the discharge rate of (NH₂)₂CNH₂⁺ ions determines the first stage of HER, the second stage occurs by the Tafel reaction. An increase in the initial concentration of guanidine stimulates HER and slightly varies the hydrogen diffusion flow into metal.     

Influence of 1,2-diaminoethane on the mechanism of aluminium corrosion in sulphuric acid solutions

The influence of 1,2-diaminoethane (DAE) on aluminium corrosion in H₂SO₄ solutions (pH 3) was investigated. In pure H₂SO₄, rapid uniform corrosion is followed by inhibition due to the formation of stable Al-sulphate binuclear bidentate metal bound surface complexes via a ligand exchange mechanism with two neighbouring sites. Metastable pitting is also observed. DAE acts as a strong corrosion inhibitor for both uniform and localised corrosion, due to the formation of Al-DAE monodentate hydrogen-bond surface complexes either by direct adsorption of the protonated molecule on Al-OH sites or via a ligand exchange mechanism with the proton of an site.     

Effect of Chloride Ions on the corrosion behaviour of iron-nickel alloys in sulphuric acid solutions

The effect of chloride ions on the corrosion behaviour of binary iron-nickel alloys in sulphuric acid solutions has been investigated using polarization resistance and potentiodynamic polarization measurements. A moderate inhibition effect of the chloride ions on the corrosion of these alloys has been found, which depends on the pH of the medium, as well as on the composition and the structure of the alloys investigated. It has been shown that the action of the chloride ions on the partial corrosion reactions is reflected by an inhibition of the cathodic hydrogen evolution reaction and by an activation of the anodic metal dissolution reaction, the first effect being stronger. Using atomic absorption analysis it has been established that no preferentional dissolution of the alloy components in the presence and in the absence of chloride ions occurs during the corrosion of the iron-nickel alloys.     

Tryptamine as a green iron corrosion inhibitor in 0.5 M deaerated sulphuric acid

The inhibition effects of tryptamine (TA) on the corrosion behaviour of ARMCO iron in 0.5 M deaerated H₂SO₄ (in the 25-55 °C temperature range) was studied in both short and long time tests (1, 24 and 72 h) by means of potentiodynamic curves (PCM) and electrochemical impedance spectroscopy (EIS). TA was found to be an effective ARMCO iron inhibitor, even at 55 °C and 72 h, but only at 10 mM. At this concentration the inhibition percentages (IP%), calculated by PCM and EIS, ranged from 90% to 99% and did not diminish over time and as the temperature increased. TA adsorption followed Bockris-Swinkels’ isotherm (x=1). The thermodynamic data indicated that, in the more concentrated solutions, TA also chemisorbed on the iron surface.     

Copper electrodeposition from cuprous chloride solutions containing lead, zinc or iron ions

Cuprous chloride hydrochloric acid solutions were electrolysed in a two compartments cell without agitation for copper extraction. It is found that the current density affects the colour and the size of copper deposits. During electrodeposition of copper from cuprous solution in the presence of various concentrations of lead, zinc or iron ions at different current densities, it is observed that lead isIn all experiments, the current efficiency for the copper codeposited with copper by increasing current density.deposition reaction fluctuates between 88.50% and 95.50%。     

Effect of molybdate ions as corrosion inhibitors of iron in neutral aqueous solutions

Abstract

The effect of molybdate ions on the corrosion of Fe in neutral solutions was investigated by electrochemical measurements (dc polarisation and impedance spectroscopy) together with gravimetric determinations. Studies were conducted in solutions containing sodium hydrogen/sodium sulphate salts with molybdate concentrations ranging between 10^?4 and 10^?2M at pH 8 and 9. Mass loss measurements indicated that about 10^?3M of molybdate was necessary in order to inhibit completely the corrosion of Fe at room temperature. The potentiodynamic polarisation and electrochemical impedance studies gave indications about the mechanism of action of the MoO^2?₄ ion. They also showed that the inhibiting effect of the oxyanion is increased in the presence of dissolved oxygen. Spontaneous passivation of the corroding Fe electrode could happen only in the presence of dissolved oxygen at concentrations greater than 10^?4M. However, passivity was also obtained under potentiodynamic polarisation conditions in deaerated solutions. The effect of the oxygen was attributed to displacement of the corrosion potential into the region of selfpassivation of the steel. Finally, the results indicated that the corrosion inhibition of Fe in neutral solutions by molybdate ions was largely insensitive to pH over the range from 8 to 9.     

The effect of sorbed hydrogen on the corrosion potential of iron in acidic sulfate solutions

By using a bipolar electrode, i.e., a membrane, it is shown that hydrogen absorbed by a metal does not virtually affect the cathodic evolution of hydrogen. The change in the iron corrosion potential is determined by the effect of sorbed hydrogen on the anodic process.Translated from Zashchita Metallov, Vol. 41, No. 1, 2005, pp. 52–55.Original Russian Text Copyright © 2005 by Nenasheva, Marshakov.     

Synergistic influence of iodide ions on the inhibition of corrosion of C-steel in sulphuric acid by some aliphatic amines

The synergistic influence caused by iodide ions on the inhibition of corrosion of C-steel in 1 M H₂SO₄ in the presence of some aliphatic amines has been studied using weight loss, potentiodynamic polarization, linear polarization and a.c. impedance techniques. Aliphatic amines used inhibit the corrosion of C-steel and the inhibition efficiency increases by increasing the concentration of the additives and also by addition of iodide ions. The adsorption of these compounds is found to obey Frumkin’s adsorption isotherm. The increase in surface coverage in the presence of iodide ions indicates that iodide ions enhance the adsorption of these aliphatic amines on the metal surface. Defines and evaluates synergism parameter (S_θ). Values of the parameter which are more than unity indicate the fact that the enhanced inhibition efficiency in the presence of iodide ions is only due to synergism and there is a definite contribution from the inhibitors molecules, which are adsorbed by coulombic interaction on the metal surface, where iodide ions are already adsorbed and thus reduces the corrosion rate.     

Inhibition of iron corrosion in acid solutions by Cefatrexyl: Behaviour near and at the corrosion potential

The corrosion inhibition of iron in HCl, HClO₄, H₂SO₄ and H₃PO₄ solutions (1M for each) by cefatrexyl has been studied by polarization resistance (R_p) and electrochemical impedance spectroscopy (EIS) at the corrosion potential. The results obtained at 30 °C revealed that cefatrexyl acts as a weak inhibitor in HCl solution while it shows excellent inhibition performance in the remaining acids. Adsorption of cefatrexyl in HCl solution obeys Langmuir’s isotherm with a very low value of the free energy of adsorption (physisorption) while its adsorption in the other acids follows Temkin’s isotherm with very high negative values of (chemisorption). Data obtained from EIS measurements were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The calculated values of the apparent activation energy (E_a) and the pre-exponential factor (λ) indicate that cefatrexyl blocks nearly the whole active centers of iron surface in H₃PO₄ solution even at elevated temperatures. The inhibition mechanism of cefatrexyl was discussed.     

Dissolution of Ti wires in sulphuric acid and hydrochloric acid solutions

Ti wire electrodes were immersed in acidic solutions containing H₂SO₄ and HCl of various concentrations at 353 K to evaluate corrosion rate by measurement of electric resistance change (resistometry). Addition of hydrochloric acid to sulphuric acid solution promoted depassivation of Ti. After depassivation, the immersion potential dropped to the hydrogen evolution potential and a hydride layer was formed on the surface. The hydride layer dissolved continuously in the acidic solution. SEM observation showed that Ti wires dissolved almost uniformly in the early stage and that the dissolution then trace became irregular due to nonuniform growth of the hydride layer. Dissolution rate of a Ti wire was estimated almost accurately by resistometry.     

Inhibition effects of LAB and LABS on iron corrosion in chlorine solutions at different temperatures

In this study, the corrosion of iron is studied using gravimetric and potentiodynamic polarization method at different temperatures and at pH 9 level in 0.1 M NaCl solutions containing different concentrations of linear alkyl benzene (LAB) and linear alkyl benzene sulphonate (LABS). Potentiodynamic polarization experiments show that corrosion rate in presence and absence of LAB and LABS increases with increasing temperature from 303 to 338 K. The corresponding activation energies are determined. Moreover, the protective film formation on metal surface is investigated by means of FTIR. It has been concluded from the results that LABS is more effective in preventing iron corrosion than LAB.