Search results

Cyclic voltametry and potentiodynamic single sweep techniques are used to study the electrochemical behaviour of lead in Na₂CO₃ solutions containing various concentrations of ClO₄^‐ as aggressive anion. The effects of different concentrations, in terms of destruction of passivity and initiation of pitting corrosion, were monitored with reference to the change in integrated anodic charge. It was found that Δq_a (taken as a measure of the extent of pitting) varies linearly with log C_ClO4‐. The pitting corrosion potential, E_pitting, varies with log C_ClO4‐ according to sigmoidal curves. These curves are explained on the basis of formation of passive, active and continuously propagating pits. Additions of aliphatic amines shift the pitting corrosion potential, E_pitting, into the noble (positive) direction, indicating the inhibition action of the added amines on the pitting attack. E_pitting varies with the logarithm of the inhibitor concentration according to: E_pitting = a + b log C_inh. The inhibition of pitting corrosion by the aliphatic amines is assumed to be due to either competitive adsorption between the CO₃^2– with ClO₄^‐ anions, and/or the chemisorption of the amine on the metal with the formation of a metal‐nitrogen coordination bond. The efficiency of these compounds as pitting corrosion inhibitors increases with the increase in the chain length of the alkyl group.

The cathodic polarization of Ni in hydrochloric acid solutions has been investigated using the galvanostatic technique. The rate of hydrogen evolution reaction was found to depend on the concentration and pH of the solution. The reaction order with respect to hydrogen ion was found to be one. The rise of temperature enhances the rate of hydrogen evolution reaction. The activation energy, \triangleH*, for such process was found to be 10kcal. mol^‐1. The effect of aniline and some of its derivatives (o‐, m‐ and p‐anisidine) on the cathodic polarization of nickel in 1M HCl solution was also studied. These compounds were found to inhibit the rate of hydrogen evolution reaction without affect on its mechanism. The inhibition efficiency depended on the concentration and type of the inhibitor. The inhibition efficiency ranged between 73 and 92 per cent at the highest concentration (10^‐2M), and ranged between 24 and 60 per cent at the lowest concentration (10^‐4M). This corresponded to surface coverage of the metal by the inhibitor. The degrees of surface coverage, θ, were calculated and found to increase with the inhibitor concentration. The results show also that, the inhibitors were adsorbed on the nickel surface according to Langmuir adsorption isotherm.

To investigate the capability of a series of nitrogen‐based heterocyclic organic compounds in inhibiting corrosion of iron in HCl and elucidate the dominant active form of the applied compounds during the adsorption process to explore the mechanism of their action.

The tested compounds were pyrimidine containing compounds, which were selected, based on molecular structure considerations. Gravimetric method has been applied with various electrochemical techniques (polarisation resistance, polarisation curves and electrochemical impedance spectroscopy) to investigate inhibition efficiency and mechanism.

The inhibiting action of the investigated pyrimidine containing compounds depends primarily on their concentration and molecular structure. These compounds act as mixed type inhibitors and function via adsorption on the surface, which follows Frumkin adsorption isotherm. The inhibition by the tested pyrimidine derivatives could be attributed to their chemisorption on the metal surface forming donor/acceptor type of bond between the inhibitor molecules and the vacant d orbitals of the surface iron atoms. Contribution from electrostatic adsorption, via interaction between the protonated form of the inhibitor and the charged metal surface, is also possible.

The applied inhibitors were tested in the presence of chloride ions as a corrosive medium. Whether these inhibitors will function well in the presence of other ions that are typically present in natural corrosive environment is unknown.

This paper provides useful information regarding inhibition effect of pyrimidine and series of its derivatives. The outcome of this work contributes to better understanding of the mechanism of inhibition by this class of N‐based heterocyclic organic compounds.

The results of the corrosion of metals and alloys with the use of solvent mixtures covering a wide range of compositions are limited in the literature. These mixed solvent systems possess a wide range of viscosity, dielectric constant and acid‐base properties. With this view, a kinetic study on the corrosion of metals in different aquo‐organic solvent systems has been undertaken. The corrosion of metals and alloys is strongly affected by the presence of water, the latter being found to have a passivating effect and sometimes a passivity breakdown effect. It is therefore of much interest to study the influence of varying water concentration on the corrosion and electrochemical behaviour of metal and alloys. The present work is a continuation of our studies on the kinetic of corrosion of metals in mixed aqueous‐organic solvents. Also, the corrosion rates are correlated to the dielectric constant and the total number of moles (n1 + n2) of water and ethylene glycol. This latter new correlation is described by El‐Shazly et al. for calculating the chemical potential (Δμ*) from kinetic data and molar thermodynamic excess functions for binary mixtures.

The inhibition of marine corrosion of steel by 6‐amino‐2‐thiouracil (I) and its derivatives 6‐benzylideneamino‐2‐thiouracil (II) and 6‐p‐chlorobenzylideneamino‐2‐thiouracil (III) has been tested on laboratory scale using electrochemical technique which was performed on mild steel in sea water medium and on field scale through the incorporation of the compounds individually in marine paints compositions. The paints containing the compounds were applied on unprimed steel and the coated panels were tested in Alexandria Eastern Harbour water (Egypt). The electrochemical measurements indicated that both compounds (I) and (III) acted as cathodic‐type inhibitors, but the data of compound (II) showed neither cathodic nor anodic inhibition. Two marine paint compositions were prepared using different binder materials. The three compounds were added individually in both paint compositions. The paint composition based on the soluble resin material as a sole binder and containing compound (I) showed the best corrosion protection of its steel surface till more than two months followed by the paint composition containing compound (III). The same paint containing the compounds showed antifouling property for four months.

The purpose of this paper was to test the extract of barley as an environmentally friendly inhibitor for the acid corrosion of steel due to its wide availability as a popular major crop and its richness with different chemical constituents reported in literature (40) like alanine, glycine, serine, aspartic acid, leucine, valine, tyrosine and isoleucine with various number of functional groups that are able to chelate metal cations and to discuss the effect of temperature on its inhibition efficiency.

Electrochemical impedance spectroscopy (EIS) and polarization measurements were carried out using frequency response analyzer Gill AC instrument. The frequency range for EIS measurements was 0.1 ≤ f ≤ 1 × 103 with an applied potential signal amplitude of 10 mV around the rest potential. Polarization measurements were carried out at a scan rate of 30 mV/min, utilizing a three-electrode cell. A platinum sheet and saturated calomel electrode were used as counter and reference electrodes, respectively. The working electrode was constructed with steel specimens that have the following composition (weight per cent): C, 0.21; S, 0.04; Mn, 2.5; P, 0.04; Si, 0.35; and balance Fe.

Barley extract could act as an effective corrosion inhibitor for the acid corrosion of steel. The inhibiting action of the barley extract was attributed to its adsorption over the metal surface that blocks the available cathodic and anodic sites. Adsorption isotherms indicated that the adsorbed extract molecules cover one active center over the metal surface.

The research included the first use of an important world crop as an effective corrosion inhibitor that can reduce the corrosion of steel to an extent of 94 per cent.

This study aims to synthesize two organic heterocyclic compounds, (2E,3E)-6-chloro-2,3-dihydrazinylidene-1-methyl-1,2,3,4-tetrahydroquinoxaline (MR1) and (2E,3E)-2,3-dihydrazinylidene-1-methyl-1,2,3,4-tetrahydroquinoxaline (MR2), characterize them using nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR) and evaluate their effectiveness as corrosion inhibitors in an acidic environment (15% HCl).

The synthesized compounds, MR1 and MR2, were tested for their corrosion inhibition properties using potentiodynamic polarization and electrochemical impedance spectroscopy. Post-corrosion, the steel surface was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) to confirm the adsorption of the compounds. The experimental findings were further supported by density functional theory calculations and molecular dynamics simulations.

The results indicated that both MR1 and MR2 exhibit significant anticorrosive activity in a 15% HCl environment. The analyses performed with SEM, EDX and AFM confirmed the effective adsorption of the inhibitors on the steel surface, forming a protective layer. Theoretical studies provided additional insights into the adsorption mechanisms and stability of the inhibitors.

This work introduces novel organic heterocyclic compounds based on quinoxalinone as effective corrosion inhibitors in acidic environments. The combined experimental and theoretical approach provides a comprehensive understanding of their anticorrosive behavior.

To investigate the inhibitive effect of gum arabic (GA) for the corrosion of aluminium in alkaline (NaOH) medium and determine its adsorption characteristics. The present work is another trial to find a cheap and environmentally safe inhibitor for aluminium corrosion.

The inhibition efficiency (%I) has been evaluated using the hydrogen evolution (via the gasometric assembly) and the thermometric methods at 30 and 40°C. The concentrations of GA (inhibitor) used were 0.1‐0.5 g/l and the concentrations of NaOH (the corrodent) were 0.1‐2.5 M. The mechanism of adsorption inhibition and type of adsorption isotherms were proposed from the trend of inhibition efficiency with temperature, E_a, ΔG_ads and Q_ads values.

GA inhibited the corrosion of aluminium in NaOH solutions. The inhibition efficiency increased with increase in GA concentration and with increase in temperature. Phenomenon of chemical adsorption is proposed for the inhibition and the process followed the Langmuir and Freundlich adsorption isotherms. The results obtained in this study for the %I were comparable for the two methods used and were corroborated by kinetic and thermodynamic parameters evaluated from the experimental data.

Further investigations involving electrochemical studies such as polarization method will enlighten more on the mechanistic aspect of the corrosion inhibition.

This paper provides new information on the possible application of GA as an environmentally friendly corrosion inhibitor even in highly aggressive alkaline environments. It has not been published elsewhere.

Introduction Recently, a new type of corrosion inhibitor, namely drag‐reducing polymer, has been developed for combating diffusion‐controlled corrosion of metals subjected to turbulent flow. The mechanism of inhibition is based on the ability of some high‐molecular‐weight polymers to damp turbulent eddies at the corroding surface with a consequent increase in the diffusion layer thickness, across which transfer of dissolved oxygen (depolarizer) or corrosion products takes place. This gives rise to a considerable decrease in the rate of metallic corrosion. Along with corrosion inhibition, the damping of turbulent eddies leads also to a reduction in the friction between the turbulently flowing fluid and the metallic surface, with a consequent decrease in the power required to move the fluids. The majority of previous studies on the use of drag‐reducing polymers as corrosion inhibitors have been conducted using turbulent flow in pipelines.

The paper aims to examine the inhibition effect of NiO nanoparticles and the influence of liquid nitrogen immersion on the corrosion behavior of (NiO)_x(Bi_1.6 Pb_0.4)Sr₂Ca₂Cu₃O_10-δ and (NiO)_x (Bi, Pb 2223), where x = 0.00 and 0.05 Wt.% phase superconductor in 0.1 M Na₂SO₄ at 30°C.

This study was done using open-circuit potential electrochemical impedance spectroscopy, potentiodynamic polarization curves and chronoamperometry measurements.

Potentiodynamic polarization technique showed that NiO nanoparticles suppress both the anodic and cathodic parts of the polarization curves of (NiO)_x(Bi, Pb)-2223 superconductor in 0.1 M Na₂SO₄ solution. A significant enhancement in the corrosion resistance of the prepared superconductors is observed on immersing them in liquid nitrogen. This is owing to the fact that immersion in liquid nitrogen increases the volume contraction of the superconductor matrix, causing the shrinkage of the pores and voids present in the samples and thus reducing the active surface area for the dissolution of (NiO)_x(Bi, Pb)-2223 superconductor matrix.

This paper fulfills the need to investigate the corrosion behavior of superconductors and the influence of liquid nitrogen immersion on such behavior.