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 electrochemical behaviour of zinc in different concentrations of Na₂SO₄ (pH = 6.0) was investigated using the potentiodynamic anodic polarization single sweep and cyclic voltammogram techniques. The anodic portion is characterized by one distinct peak corresponding to Zn(OH)₂ or ZnO. This is followed by a passive region up to a certain potential; the passive current suddenly rises steeply without any sign of oxygen evolution. This denotes the breakdown of the passive film and initiation of pitting corrosion. It was found that the breakdown potential depends on the sulphate concentration, type of aeration, scan rate, solution temperature and pH. The pitting initiation may be explained through the adsorption of SO₄^2– anion on the oxide film formed. This decreases the repair efficiency and causes further metal dissolution. From the cyclic voltammogram of zinc in different concentrations of Na₂SO₄, it was found that the change in the integrated anodic charge, Δq_a, which is taken as a measure of the extent of pitting, varies linearly with concentration of SO₄^2– anion.

The potentiodynamic anodic polarization curves for the lead electrode were obtained in 0.1 mol L‐1 KOH solution in the absence and presence of C103‐ or C104‐ as aggressive ions at different concentrations. Lower concentrations of these ions have no significant influence on the passive film, while higher concentrations raise the active dissolution current density, and cause destruction of passivity and initiation of pitting corrosion. The critical pitting corrosion potential varies with the concentration of the aggressive ions according to sigmoidal curves. These curves were explained on the basis of the formation of passivitable, active and continuously propagagting pits depending on the range of the aggressive ion concentration. Additions of increasing concentrations of chromate, phosphate, sulphate and carbonate ions cause a shift of the critical pitting potential in the noble direction accounting for increase resistance to pitting attack (inhibition). The pitting corrosion potential varies with the concentration of the inhibitive ions, in the presence of a constant concentration of the aggressive ions, according to curves of sigmoidal shape. From these curves one can determine the minimum concentration of the inhibitive ions necessary for inhibition of pitting corrosion to occur.

Corrosion inhibitors are widely used in industry, although in many cases their surface chemistry is not well understood. Several nitrogen‐containing organic compounds have been used as corrosion inhibitors. Corrosion inhibition is a surface process which involves the specific adsorption of inhibitors on the metal surface. The extent of inhibition of metallic corrosion may depend on the nature of the metal surface and extent of adsorption of the inhibitor. The type of interaction of the inhibitor on the metal surface during corrosion has been deduced from its adsorption characteristics.

The purpose of this paper is to study the electrochemical behavior of Sn electrode in Na₂B₂O₇ solutions in the absence and presence of NaNO₃ as a pitting corrosion agent.

The electrochemical behavior of Sn electrode was studied by using cyclic voltammetry and potentiodynamic polarization measurements and complemented with scanning electron microscopy examinations.

This paper shows that in the absence of NO₃ − ions, the anodic polarization of Sn electrode exhibits active/passive transition. Addition of various concentrations of NO₃ − anions to the borate solution enhances active anodic dissolution and tends to break down the passive oxide film at a certain pitting potential. The pitting potential, and hence the pitting corrosion resistance, decreases with increasing NO₃-ion concentration and temperature but increases with scan rate and repetitive cycling. Addition of CrO₄²⁻, WO₄²⁻ or MoO₄²⁻ oxyanions to the borate nitrate solution inhibits the pitting corrosion of Sn.

This is the first study that shows the effect of NO₃ − ion as a pitting corrosion agent.

Copper and its alloys are widely used in industries because of their good resistance to corrosion and are often used in cooling water systems. Brass has been widely used for shipboard condensers, power plant condensers and petrochemical heat exchangers. Brass is susceptible to the corrosion process known as dezincification by means of which brass looses its valuable physical and mechanical properties leading to failure of structure. The aim of this investigation was to control the dezincification of brass in 3 per cent NaCl solution using benzotriazole (BTA) derivatives.

BTA derivatives namely 1‐hydroxymethylbenzotriazole (HBTA) and N,N‐dibenzotriazol‐l‐ylmethylamine(ABTA) were synthesised and their inhibition behaviour on brass in 3 per cent NaCl solution was investigated by the weight‐loss method, potentiodynamic polarisation, electrochemical impedance and solution analysis techniques. The morphology of the brass after corrosion in the presence and absence of the BTA derivatives was examined using scanning electron microscopy (SEM).

Potentiodynamic polarisation studies showed that the BTA derivatives investigated were mixed type inhibitors, inhibiting the corrosion of brass by blocking the active sites of the brass surface. Changes in the impedance parameters (charge transfer resistance and double layer capacitance) were related to the adsorption of BTA derivatives on the brass surface, leading to the formation of a protective film. Solution analysis revealed that the BTA derivatives excellently controlled the corrosion of brass. SEM micrographs showed the formation of compact surface film on the brass surface in the presence of inhibitors, thereby providing better corrosion inhibition.

Contributes to research on corrosion protection for copper and its alloys.

The purpose of this paper is to study the corrosion inhibition of carbon steel (CS) using a “green” inhibitor, polyvinyl pyrrolidone (PVP), in an aerated, alkaline medium containing 0.1M NaCl (blank) at pH 9 and pH 10. The effects of some additives, such as KI and untreated Saudi clay (UC) were investigated.

Weight loss method, surface studies, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation were applied.

The inhibition efficiencies of blank solutions with 1000 ppm PVP ranged from 66‐78% for weight loss results and from 23‐66% for the electrochemical tests. The EIS results indicated that the adsorption of PVP led to the formation of a protective film on the metal/solution interface. Tafel results indicated that PVP is a mixed‐type inhibitor. The addition of KI to PVP and the blank solution significantly increased inhibition efficiency, while the addition of UC reduced the inhibition efficiency. Adding KI resulted in a high surface‐area coverage ranging from about 91% after one hour to about 81% after 45 hours. The adsorption mechanism was fitted with a Langmuir isotherm.

This is a static study, whereas in oil drilling there is a dynamic system; however the findings may apply to both systems.

Carbon steel is used in alkaline and neutral media in the petroleum industry. The effect of KI additives was examined.

The paper shows how it may be possible to reduce the cost of repair of equipment and lower the environmental impact of corrosion.

There are few studies which investigate the combining effect of polymer and KI in alkaline medium containing NaCl.

The purpose of this paper is to study the inhibition effect of (6-phenyl-3-oxopyridazin-2-yl) acetohydrazide (GP4) on the corrosion of mild steel in acidic medium by gravimetric measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS).

Weight loss measurements, potentiodynamic tests and EIS were performed during this study.

(6-phenyl-3-oxopyridazin-2-yl) acetohydrazide (GP4) was found to be a very efficient inhibitor for mild steel in 1.0 M HCl solution, reaching about 85 per cent with inhibitor concentration 1.0 × 10-3 M at 303 K.

(6-phenyl-3-oxopyridazin-2-yl) acetohydrazide (GP4) was found to play an important role in the corrosion inhibition of mild steel in acidic solution.

This paper is intended to be added to the family of pyridazine derivatives which are highly efficient inhibitors and can be used in the area of corrosion prevention and control.

Aluminum tripolyphosphate was used as a corrosion inhibitor in a simulated concrete pore solution. For studies of the inhibition mechanism of aluminum tripolyphosphate on the carbon steel, its influence on the pitting initiation on the carbon steel in a Cl⁻ containing pore solution were investigated.

Potentiodynamic polarization curves, Mott–Schottky plots and potentiostatic polarization of the carbon steel in the pore solution with different content of aluminum tripolyphosphate were measured, as well as the optical micrographs of pitting on the carbon steel was observed.

The metastable pitting potential and the stable pitting potential increased, while the donor density and the flat band potential decreased with the concentration of aluminum tripolyphosphate in solution. Furthermore, the initiation of pitting was suppressed, as well as the transition from metastable to stable pitting was hindered by the aluminum tripolyphosphate. The scale parameter (a), in the extreme distribution of the maximum current peak, could be used to predict the transition from metastable to stable pitting.

The inhibition mechanism of aluminum tripolyphosphate on carbon steel in pore solution was revealed. It suppresses the initiation of pitting and hinders the transition from metastable to stable pitting. Furthermore, a parameter defined as the scale parameter (a) in the extreme distribution of the maximum current peak was introduced to predict the transition from metastable to stable pitting.

Corrosion of steel in marine environments poses a significant economic and environmental challenge because of its detrimental effects on marine structures and equipment. Traditional chemical inhibitors that mitigate corrosion often introduce harmful substances into the environment. As a result, there is a growing interest in exploring eco-friendly alternatives, such as plant-derived inhibitors, to reduce the environmental impact of corrosion protection strategies. The purpose of this study is to investigate the effectiveness of Phyllanthus urinaria extract as a green anti-corrosion additive for rebar steel in marine conditions.

Phyllanthus urinaria extract was prepared in the ethanol solution with the assistance of a sonicator. The steel’s surface upon addition of the extract was characterized using SEM, EDX and FTIR analysis. The electrochemical corrosion characteristics, including potentiodynamic polarization and electrochemical impedance spectroscopy, were used to evaluate the inhibitory performance of the extract on steel under simulated marine conditions (3.5% NaCl solutions).

The results of this study showed that with Phyllanthus urinaria extract’s content of 0.02% in NaCl solution of 3.5%, the corrosion rate decreased to about 30% compared to the controlled sample. Measurements of the inhibitory mechanism analysis study for all solutions from 0 mg/L to 1.114 mg/L of polyphenol from Phyllanthus urinaria extract showed a significant reduction in rebar corrosion rate, especially with 0.2228 mg/L polyphenol. Reinforcement can increase corrosion inhibition by up to 30% compared to the control sample.

To the best of the authors’ knowledge, this is the first study of using Phyllanthus urinaria extract as green inhibitor for protection of steel from the corrosion in the simulated marine solution. The protective mechanism for steel using Phyllanthus urinaria extract was investigated using the FTIR, SEM, EDX and electrochemical analysis. The results indicated that the polyphenols in the extract showed inhibition that could minimize the corrosion of reinforcement in marine environments.