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Zn‐Al alloys are widely used as coatings for corrosion protection of steel. These alloys provide long‐term protection to steel in several aqueous media; however, little attention has been paid to their behaviour in acidic media. The aim of this investigation is to study the corrosion and inhibition of 90 per cent Zn‐10 per cent Al alloy in hydrochloric acid.

Pyridine and a number of its methyl‐containing derivatives were applied in controlling the corrosion of 90 per cent Zn‐10 per cent Al alloy. The inhibitive action and mechanism of these compounds were investigated by weight loss tests, linear polarisation resistance measurements, galvanostatic polarisation tests and electrochemical impedance spectroscopy.

It was found that the corrosion rate of this alloy was much higher than that of either Zn or Al alone. Pyridine and its derivatives exhibited good inhibition for the corrosion of 90 per cent Zn‐10 per cent Al alloy, their inhibition efficiency increased in the order: I < II < III < IV. Potentiodynamic polarisation studies revealed that the investigated pyridine derivatives were mixed‐type inhibitors and functioned by adsorption on reactive sites on the alloy surface through the influence of the nucleophilic nitrogen atom forming a good physical barrier to prevent access of aggressive ions to the alloy surface. This was supported by the impedance measurements which showed a change in the charge transfer resistance and double layer capacitance indicating adsorption on the alloy surface. It was shown that the introduction of the methyl group(s) into the pyridine ring enhanced the effectiveness of pyridine inhibition. The improvement was attributable to the electron‐donating tendency of this group that gives rise to the increase in the electron density at the adsorption site. All the investigated substituents showed negative values of the Hammett constant (σ), indicating their electron‐donating property. The negative value of this constant increased according to the order: I < II < III < IV, the greater the negative value of σ being consistent with the greater degree of corrosion inhibition. It also was revealed that the presence of these inhibitors increased the value of activation energy for corrosion with a ranking order that was consistent with that of their inhibition effectiveness.

The evaluated inhibitors assured significant corrosion inhibition of the Zn‐Al alloy in HCl, however, their behaviour in different acid media was ambiguous.

This paper makes significant contibution to understanding the corrosion and inhibition of one of the widely apply coatings for steel protection in one of the most widely used aqueous mineral acids in industry.

The purpose of this paper is to investigate the effect of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) and blended formulations on the corrosion inhibition of aluminium in HCl solutions at 30-60°C and to study the mechanism of action.

The inhibitive effect of the homopolymers and polymer blend was assessed using weight loss and hydrogen evolution methods at 30 and 60°C. The morphology of the corroding aluminium surface without and with the additives was visualized using atomic force microscopy. The trend of inhibition efficiency with temperature was used to propose the mechanism of inhibition and type of adsorption.

Results obtained show that inhibition efficiency (η%) increases with increase in concentration of the polymers but decreases with increase in temperature. The inhibition efficiency of the homopolymers and their blends decreased with rise in temperature. Inhibition efficiency was found to be synergistically enhanced on blending the two homopolymers with highest inhibition efficiency obtained for (PEG:PVP) blending ratio of 1:3. The phenomenon of physical adsorption is proposed from the trend of inhibition efficiency with temperature.

The mechanistic aspect of the corrosion inhibition can be better understood using electrochemical studies such as potentiodynamic polarization and electrochemical impedance spectroscopy.

Studies involving the use of polymer blends/mixtures as corrosion inhibitor for metals in corrosive environments are scarce. The results suggest that the mixture could find practical application in corrosion control in aqueous acidic environment. The data obtained would form part of database on the use of polymer–polymer mixtures to control acid-induced corrosion of metal.

To study and compare the inhibition effects of eco‐friendly inhibitors of sodium silicate and 1‐hydroxyethylidene 1,1 diphosphonic acid (HEDP) in corrosion control and prevention of soft water discolouration (red water) in carbon steel pipelines.

Electrochemical impedance and Tafel polarization measurements were used to study corrosion inhibition properties. The experiments were carried out under different concentration ratios of inhibitors. Different hydrodynamic conditions were applied to simulate pipeline fluid flow. Scanning electron microscopy (SEM) and EDAX analysis were used for surface studies.

It was observed that corrosion inhibitor combinations under static conditions showed synergistic effects at low concentrations. The inhibition efficiency and synergistic behaviours of inhibitors were enhanced as the electrolyte turbulence was increased. In addition, the inhibitor concentration value required to reach maximum inhibition decreased. It was found that at 20 ppm sodium silicate and 5 ppm HEDP, co‐inhibition efficiencies increased significantly to more than 90 per cent and the corrosion rate decreased far below 1 mpy as the electrode rotational speed was increased. Surface studies using SEM revealed the formation of a compact and uniform film of co‐inhibitors.

The results of this paper can be used for the development of effective, non‐toxic and economically attractive corrosion inhibitor formulations for soft water transmission pipelines.

The observed synergistic behaviour can be due to the incorporation of the silicate gel‐like network through organic phosphorous bonds. The hydrodynamic condition of the electrolyte leads to enhancement of inhibition efficiency, which indicates that the corrosion inhibition was mass transfer controlled.

This paper seeks to investigate the different inhibition performance and adsorption behaviour of dodecylamine in acidic and neutral environments and to understand further the inhibition mechanism of dodecylamine in CO₂‐saturated brine solution.

The inhibition performance and adsorption behaviour of dodecylamine on N80 steel in CO₂‐saturated brine solution in acidic and neutral environments were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy and the attenuated total reflection‐Fourier transform infrared spectroscopy.

Corrosion potentials exhibited a pronounced shift in the positive direction at higher concentrations of dodecylamine. The inhibition efficiency of dodecylamine was shown to be pH‐dependent. The effective inhibition concentration of dodecylamine decreased from pH 4.9 to 7.4. In a neutral environment, the inhibitor was shown to affect the deposition of the corrosion products and provide more active sites to bond with the inhibitor. More alkaline environments made the electron cloud density of dodecylamine much higher, which was more favourable to the interaction of dodecylamine and the naked metal base, and hence dodecylamine had a much better inhibition performance in a neutral environment than in acidic environments.

This paper provides information regarding the inhibition performance and adsorption behaviour of dodecylamine on N80 steel and probes the inhibition mechanism of dodecylamine in acidic and neutral environments. The results of the work contribute to an understanding of the inhibition mechanism of the inhibitor in different environments, which will be useful for effective design and choice of inhibitors in CO₂ corrosion.

To appraise the inhibiting effect of Ocimum basilicum extract on aluminium corrosion in 2 M HCl and 2 M KOH solutions, respectively, at 30 and 60°C.

Corrosion rates were determined using the gas‐volumetric technique and the values obtained in absence and presence of extract was used in calculation of the inhibition efficiency. The mechanism of inhibition was estimated from the trend of inhibition efficiency with temperature.

Ocimum basilicum extract was found to inhibit aluminium corrosion in the acidic and alkaline environments. Inhibition efficiency increased with extract concentration but decreased with rise in temperature, suggesting physical adsorption of the organic matter on the metal surface. These results were corroborated by kinetic and activation parameters for corrosion and adsorption processes evaluated from the experimental data at the temperatures studied. Halide additives synergistically improved the inhibition efficiency of the extract.

This paper provides new information on the possible application of Ocimum basilicum extract as an environmentally friendly corrosion inhibitor. The mixed extract – iodide formulation provides an effective means for retarding aluminium corrosion even in highly aggressive alkaline environments.

To investigate the effect of halide ions on the corrosion inhibition of mild steel using polyvinyl alcohol (PVA) in H₂SO₄ at 30‐60°C and to study the mechanism of action.

The corrosion rates were determined using the gravimetric (weight loss) and gasometric (hydrogen evolution) techniques. The results obtained in the absence and presence of PVA, halides, PVA – halides combination were used to calculate the inhibition efficiency (%I), degree of surface coverage and to propose the mechanism of inhibition and type of adsorption.

Results obtained showed that inhibition efficiency (%I) increased with the increase in concentration of PVA, on the addition of halides and with the increase in temperature. Phenomenon of chemical adsorption was proposed and PVA was found to obey Langmuir, Flory‐Huggins and Freundlich adsorption isotherms. The synergism parameter, S₁, evaluated was found to be greater than unity and the values of E_a, ΔH°, ΔS° and ΔG° obtained revealed that the adsorption process was spontaneous.

Electrochemical studies such as polarization and AC impedance spectra will enlighten more on the mechanistic aspects of the corrosion inhibition and more polymers need to be evaluated as corrosion inhibitors.

PVA can be used as corrosion inhibitor and the addition of halides to PVA improves the inhibition efficiency considerably.

This paper provides new information on the effects of halides on the corrosion inhibition using PVA as an inhibitor for mild steel in acidic medium. Such a study had not been reported elsewhere.

The purpose of this paper is to study the corrosion inhibition performance of an eco-friendly drug clozapine on the corrosion of copper in 1.0 M nitric acid and 0.5 M sulfuric acid solutions.

The corrosion inhibition nature of inhibitor molecule was evaluated by weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization studies. An attempt was made to correlate the molecular properties of neutral and protonated forms of inhibitor molecule using quantum chemical calculations. The effect of temperature on the corrosion inhibition efficiency was also studied using electrochemical impedance spectroscopy. The potential of zero charge was determined to explain the mechanism of corrosion inhibition.

The studies on corrosion inhibition performance of clozapine showed that it has good corrosion inhibition efficiency on the corrosion of copper in 1.0 M nitric acid and 0.5 M sulfuric acid solutions. The adsorption of clozapine molecules onto the copper surface obeyed the Langmuir adsorption isotherm. The value of free energy of adsorption calculated is very close to −40 kJmol⁻¹, indicating that the adsorption is through electrostatic coulombic attraction and chemisorption. The decrease in the value of energy of activation with the addition of inhibitor also shows the chemisorption of the inhibitor on the metal surface. The potential of zero charge and quantum chemical studies confirmed that the protonated molecules also get involved in the corrosion inhibition process through physisorption.

The present work indicates that clozapine can act as a good corrosion inhibitor for the corrosion of copper in acid media.

Phosphonic acids are good complexing agents. However, they are not good as inhibitors except for a very few. Synergistic inhibition is offered in the presence of metal cations like Ca²⁺, Mg²⁺, Zn²⁺ and others in neutral media. The zinc ion is an ideal choice. The part of zinc ions are now replaced by polymers, azoles to prepare eco‐friendly inhibitor formulations. They are also used as corrosion inhibitors in concrete, coatings, rubber blends, acid cleaners, anti‐freeze coolants, etc. Discusses the various applications of phosphonic acids and their action mechanisms.

The purpose of this paper is to study methyl green dye (MG) as a corrosion inhibitor for low carbon steel (LCS) in hydrochloric acid (1 M) and sulphuric acid (0.5 M) and to assess the effect of temperature variation and halide additives on the inhibition efficiency.

Corrosion rates are monitored using the gravimetric technique. Inhibition efficiency is determined by comparing the corrosion rates in the absence and presence of additives. Attempts are also made to elucidate the inhibition mechanism from the trend of inhibition efficiency with change in temperature and type of acid anion.

MG reduces the corrosion rate of the LCS specimens in both acid media within the investigated temperature range by adsorption at the metal/solution interface. Inhibition efficiency increases with MG concentration but decreases with rise in temperature. Maximum values of 67 and 73 per cent are obtained in 1 M HCl and 0.5 M H₂SO₄, respectively, at [MG]=0.001 mol dm⁻³. Halide additives increase the inhibition efficiency mainly in the sulphuric acid medium.

The inhibiting effect of MG is studied within a fixed concentration range, which can be expanded for further studies. The same applies to the effect of halide additives. Also, the dye structure can be modified by introducing different functional groups, and the effect on inhibition efficiency is investigated.

The research findings can find practical application for corrosion control in aqueous acidic environments.

This paper provides new information on the application of MG for corrosion inhibiting purposes. The experimental results form part of an extensive database on the corrosion inhibiting characteristics of organic dyes.

This paper aims to investigate the inhibitive effect of ethanol extracts of Garcinia kola (EXG) for the corrosion of mild steel in H₂SO₄ solutions. The study is another trial to find a cheap and environmentally safe inhibitor for mild steel corrosion.

The inhibition efficiency has been evaluated using the hydrogen evolution technique at 30‐60°C. The mechanism of adsorption inhibition and type of adsorption isotherm were proposed based on the trend of inhibition efficiency and kinetic data.

The results obtained indicate that EXG inhibits the corrosion of mild steel in acidic medium and that the inhibition efficiency increases with an increase in the concentration of ethanol extracts and decreasing temperature. The inhibition efficiency increased on addition of potassium iodide to EXG, indicating synergism. The experimental data obeyed the Langmuir adsorption isotherm as well as the El‐Awady et al. thermodynamic‐kinetic model. The activation energy of inhibition of 6.8508 KJ/mol calculated for the corrosion process suggests that the EXG molecules are physically adsorbed on the metal surface.

Further investigations involving electrochemical studies such as polarization method will provide further enlightenment on the mechanistic aspect of the corrosion inhibition.

This paper provides new information on the possible application of EXG as an environmentally friendly corrosion inhibitor under the specified conditions. This environmentally friendly inhibitor could find possible applications in metal surface anodizing and surface coatings.