Inhibition of mild steel corrosion in phosphoric acid solution by triazole derivatives

Corrosion inhibition by triazole derivatives (n-PAT) on mild steel in phosphoric acid (H₃PO₄) solutions has been investigated by weight loss and polarization methods. The results indicate that these compounds act as mixed-type inhibitors retarding the anodic and cathodic corrosion reactions with emphasis on the former and do not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. Some kinetic parameters are obtained.     

Corrosion inhibition of zinc in phosphoric acid solution by 2-mercaptobenzimidazole

The inhibiting action of 2-mercaptobenzimidazole on the corrosion of zinc in phosphoric acid (H₃PO₄) solution has been investigated by weight loss and polarization. The studies reveal that the inhibitor is effective for the inhibition of zinc in H₃PO₄ solution and retards the anodic and cathodic corrosion reactions with emphasis on the former.     

Caffeic acid as a green corrosion inhibitor for mild steel

The inhibitor effect of the naturally occurring biological molecule caffeic acid on the corrosion of mild steel in 0.1 M H₂SO₄ was investigated by weight loss, potentiodynamic polarization, electrochemical impedance and Raman spectroscopy. The different techniques confirmed the adsorption of caffeic acid onto the mild steel surface and consequently the inhibition of the corrosion process. Caffeic acid acts by decreasing the available cathodic reaction area and modifying the activation energy of the anodic reaction. A mechanism is proposed to explain the inhibitory action of the corrosion inhibitor.     

Tryptamine as a corrosion inhibitor of mild steel in hydrochloric acid solution

The inhibitor effect of tryptamine on the corrosion of mild steel in 0.5 M hydrochloric acid at 30 °C was investigated using linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increases with an increase in concentration of tryptamine. At 500 ppm tryptamine the inhibition efficiency calculated by these techniques is around 97%. Cathodic and anodic polarization curves of mild steel in the presence of different concentrations of tryptamine at 30 °C reveal that it is a mixed type inhibitor. Tryptamine follows Langmuir adsorption with adsorption free energy of −35.07 kJ mol⁻¹.     

Adsorption and inhibitive properties of benzimidazole derivatives in acid mild steel corrosion

Eight diazoles were investigated as corrosion inhibitors of mild steel in 1 M hydrochloric acid using gravimetric and polarization techniques. It was found that the inhibition efficiency increased with the increase of organic substrate concentration, while the adsorption followed the Frumkin isotherm. A correlation between the electronic parameters (induction and mesomeric effects of the substituents, ionization potential values) as well as those of the chemical structure (molecular area) of diazoles molecules and their inhibiting properties was looked for. The results obtained show that a definite interdependence exists but it is not as simple and straightforward as might be expected.     

Adsorption properties and inhibition of mild steel corrosion in sulphuric acid solution by ketoconazole: Experimental and theoretical investigation

Ketoconazole (KCZ) has been evaluated as a corrosion inhibitor for mild steel in aerated 0.1 M H₂SO₄ by gravimetric method. The effect of KCZ on the corrosion rate was determined at various temperatures and concentrations. The inhibition efficiency increases with increase in inhibitor concentration but decrease with rise in temperature. Adsorption followed the Langmuir isotherm with negative values of , suggesting a stable and a spontaneous inhibition process. Quantum chemical approach was further used to calculate some electronic properties of the molecule in order to ascertain any correlation between the inhibitive effect and molecular structure of ketoconazole.     

Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media

The inhibiting effect of two Schiff bases on the corrosion of the mild steel (MS) in 1 M HCl has been studied by electrochemical impedance spectroscopy (EIS) and Tafel polarisation measurements. The Schiff bases, 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ether (L₁) and 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ethane (L₂), were synthesized using 3-carboxaldehydethiophene and its corresponding amine. Polarisation curves reveal that both compounds are mixed type (cathodic/anodic) inhibitors and inhibition efficiency (% IE) increases with increasing concentration of compounds. It is suggested that their effects depend on their concentrations and the molecular structures. Adsorption of compounds on mild steel surface is spontaneous and obeys Langmuir’s isotherm.     

Lignin terpolymer for corrosion inhibition of mild steel in 10% hydrochloric acid medium

Lignin terpolymer has been obtained by grafting copolymerization of both dimethyl diallyl ammonium chloride (DMDAAC) and acrylamide (AM) onto lignin. The corrosion inhibition properties of the terpolymer were tested. The results showed that the highest corrosion inhibition percentage was over 95% in 10% HCl acid medium at 25 °C and 80 °C. The lignin terpolymer inhibitor adsorption followed Temkin isotherm at 25 °C and 80 °C, and the adsorption capability was in reverse proportion to the temperature according to −ΔG_ads. The effects of corrosion inhibition are the comprehensive synergistic effect through the graft reaction among lignin, AM and DMDAAC.     

Early corrosion of mild steel in seawater

Because field studies seldom recover coupons less than 6 months from immersion they provide no information about early corrosion behaviour. Linear or power law functional behaviour for corrosion loss with time is often assumed. New field studies performed on the Australian east coast and described herein using very closely spaced recoveries of coupons show that the corrosion loss-time behaviour is initially highly non-linear and then almost linear until corrosion product formation begins to control the rate of corrosion. The reasons for this behaviour are discussed in terms of the recently introduced multi-phase phenomenological model for marine corrosion. Conventional oxygen diffusion arguments are then used to provide a mathematical model to describe the main part of this behaviour. The possible influences of seawater temperature and oxygen concentration are discussed.     

An investigation of benzimidazole derivative as corrosion inhibitor for mild steel in different concentration HCl solutions

The influences of a benzimidazole derivative, namely 1,8-bis (1-chlorobenzyl-benzimidazolyl) -octane (CBO) on the corrosion behaviour of mild steel in different concentration HCl solutions were studied by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and SEM observations. The results showed that CBO acted as an excellent and a mixed-type inhibitor via strongly chemical adsorption onto mild steel surface to suppress simultaneously both anodic and cathodic processes according to the Langmuir adsorption isotherm. Inhibition efficiencies increased with increasing concentration of inhibitor and HCl. An inhibition mechanism was proposed in terms of strongly adsorption of inhibitor molecules on mild steel surface.     

Investigation on some Schiff bases as corrosion inhibitors for mild steel

In the present work, the effect of some newly synthesized Schiff bases containing sulphur nitrogen as heteroatom was investigated on mild steel corrosion in acidic media. Electrochemical studies of the mild steel samples were performed in an aerated solution of 0.1 M HCl + dimethyl sulphoxide (DMS) as co-solvent. DMS is also behaving as a corrosion inhibitor for mild steel. At low inhibitor concentration and short immersion time one can see only the inhibitive effect of DMS as anodic inhibitor for mild steel. At high concentration and long immersion time inhibition efficiencies are increased and cathodic inhibition is observed.     

Evaluation of impedance measurements on mild steel corrosion in acid media in the presence of heterocyclic compounds

Five heterocyclic compounds, having a five atom ring, fused with the benzene ring (indole, benzimidazole, benzotriazole, benzothiazole and benzothiadiazole) were investigated as corrosion inhibitors of mild steel in 1 N HCl using impedance and polarisation resistance methods. Four of these compounds exhibit inhibition properties, while one of them, benzothiadiazole, stimulates the corrosion process. Adequate structure models of the interface are offered. The experimental data show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. At high inhibitor concentrations a second time constant is observed in the impedance spectra. The values of the polarisation resistance determined by the polarisation resistance method are well correlated with the sum of the separate resistances from the impedance measurements.     

N-methyl-2-hydroxyethylammonium oleate ionic liquid performance as corrosion inhibitor for mild steel in hydrochloric acid medium

The aim of the present study is to evaluate the performance of N-methyl-2-hydroxyethylammonium oleate ([m-2HEA][Ol]) as a corrosion inhibitor for mild steel in a 0.1-mol/L hydrochloric acid solution and also investigate the role of chloride in the inhibition mechanism. This protic ionic liquid (PIL) has formerly shown a high efficiency as a corrosion inhibitor in a neutral chloride medium. Electrochemical and weight loss measurements, surface contact angle determination, scanning electron microscopy, and Raman spectroscopy were used to understand the factors that influence the response of the studied inhibitor. Results revealed that [m-2HEA][Ol] behaves as a mixed-type adsorption inhibitor, by blocking cathodic sites and by modifying the activation energy of the anodic reaction, and it can reach up to 94–97% of inhibition efficiency. PIL adsorption was enhanced by the excess of positive charge of the mild steel. The effect of inhibitor molecule has been discussed to propose a mechanism that explains the inhibitory action of the corrosion inhibitor, pointing out the role of chloride in the inhibition mechanism.     

Bis (benzimidazol-2-yl) disulphide: An efficient water soluble inhibitor for corrosion of mild steel in acid media

The inhibition effect of Bis (benzimidazol-2-yl) disulphide (BIMDS) on corrosion behavior of mild steel (MS) in 1.0 M HCl and 0.5 M H₂SO₄ was studied using different techniques. These studies have shown that studied compound is a good inhibitor for MS in 1.0 M HCl and 0.5 M H₂SO₄ solutions. Inhibitor showed better performance in 0.5 M H₂SO₄ solutions than 1.0 M HCl. Polarization measurements indicated that BIMDS is a mixed-type inhibitor in both acid media. Adsorption of inhibitor molecules on the mild steel surface showed Langmuir isotherm model in both acid media.     

Inhibitive and adsorption behaviour of carboxymethyl cellulose on mild steel corrosion in sulphuric acid solution

Chemical methods were used to assess the inhibitive and adsorption behaviour of carboxymethyl cellulose (CMC) for mild steel in H₂SO₄ solution at 30-60 °C. Results obtained show that CMC act as inhibitor for mild steel in H₂SO₄. The inhibition efficiency was found to increase with increase in CMC concentration but decreased with rise in temperature, which is suggestive of physical adsorption mechanism. The adsorption of the CMC onto the mild steel surface was found to follow Langmuir and Dubinin-Radushkevich adsorption isotherm models. The inhibition mechanism was further corroborated by the values of activation parameters obtained from the experimental data.     

Cefotaxime sodium: A new and efficient corrosion inhibitor for mild steel in hydrochloric acid solution

The corrosion inhibition of mild steel in 1 M HCl solution by cefotaxime sodium has been studied by Tafel polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurement. The inhibitor showed 95.8% inhibition efficiency at optimum concentration 300 ppm. Results obtained revealed that inhibition occurs through adsorption of the cefotaxime on metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization studies suggest that it is a mixed type of inhibitor. Electrochemical impedance spectroscopy techniques were also used to investigate the mechanism of corrosion inhibition.     

The corrosion protection of mild steel by polypyrrole/polyphenol multilayer coating

Electrochemical synthesis of very thin polyphenol (PPhe) film was achieved on polypyrrole coated mild steel electrode (MS/PPy) and a multilayer coating was obtained, cyclic voltammetry technique was used for the synthesis. The corrosion performance of this multilayer coating and single PPy coating were investigated in 0.05 M H₂SO₄ solution by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential (E_ocp)-time curves were used. It was found that the multilayer coating could provide much better protection than the single PPy coating for corrosion of MS for much longer periods and an efficiency of 98.3% was determined for this coating after 340 h exposure time in corrosive medium. It is proposed that the very thin PPhe film coated on top of PPy coating lowered the porosity and improved the barrier effect of the coating significantly.     

Temperature effect on mild steel corrosion in acid media in presence of azoles

The inhibiting properties of four azoles (indole, benzimidazole, benzotriazole, benzothiazole) were investigated in case of mild steel corrosion in 1 M HCl. The effect of temperature was followed. Impedance spectroscopy, polarization resistance, gravimetric and polarization curves methods were applied. An adequate structural model of the interface in inhibitors presence is offered and the values of the corresponding parameters are calculated. The apparent activation energy of the process taking place in an inhibitor presence was determined on the ground of five temperature values in the range from 20 °C to 60 °C using the data obtained by two independent methods. Comparative investigations were carried out in 1 M H₂SO₄ aiming to elucidate the effect of the acid’s anion. The generalization of the data obtained provided to make conclusions concerning the mechanism of the inhibitors’ adsorption.