The anodic behaviour and corrosion of tin in various concentrations (0.05–0.7 M ) of succinic acid were studied using cyclic voltammetry. The potentiodynamic anodic polarization curves exhibit active/passive transition. The active dissolution of tin involves one anodic peak. The cathodic curve exhibits one cathodic peak corresponding to the reduction of the passive layer. The ratio of the anodic charge/cathodic charge is more than unity indicating that the passive layer is very thin and the dissolution products are mainly soluble species. Additions of some polyethylene glycols to the succinic acid solution decrease the anodic peak current and shift the peak potential in the negative direction. These changes depend on the concentration and molecular weight of the polyethylene glycol added. The effect of the inhibitors decreases in the following order: (PEG) 6000 > (PEG) 4000 > (PEG) 1200 . The inhibition efficiency decreases with increase in temperature, suggesting physical adsorption.

The corrosion of tin electrode in sodium borate (Na2B4O7) solutions was investigated using cyclic voltammetry and potentiostatic current transient techniques. In absence of halide ions, the E/j response exhibits active/passive transition. The active region involves one anodic peak corresponding to the formation of Sn(OH)2 and/or SnO. Addition of Cl−, Br− or I− (C ⩽ 0.01 M) ions inhibits the active dissolution of tin, but higher concentrations enhance the active dissolution and tend to breakdown the passive film and induce pitting attack. The effect of WO42-, MoO42-, NO2- and NO3- as inorganic inhibitors on the pitting corrosion of tin in (0.1 M Na2B4O7 + 0.1 M NaCl) solution has also been studied. The presence of these anions (except NO3-) inhibits pitting corrosion. Chronoamperometry measurements showed that nucleation of pit takes place after an incubation time (ti). The rate of pit nucleation (ti-1) increases with increasing halide ions concentration and applied potentials, but decreases with increasing the concentration of the inorganic inhibitors (except NO3-). The inhibition efficiency of these inhibitors decreases in the order:WO42−>MoO42−>NO2−

The anodic behaviour of tin electrode in Na2CO3 solutions containing different concentrations of Na2ClO4 was studied by potentiodynamic technique and complemented by scanning electron microscope. In perchlorate free carbonate solutions; the polarization curves exhibit two anodic peaks assigned to the electroformation of Sn(II) and Sn(IV) species, respectively, prior to the permanent passivation region. The passivity is due to the presence of SnO and SnO2 layers on the electrode surface. Addition of ClO4- to the carbonate solution breaks down the passive layer and initiate pitting corrosion at a certain critical pitting potential. The pitting potential decreases with an increase in ClO4- concentration but increases with increasing both Na2CO3 concentration and scan rate. Addition of increasing concentration of MoO42-, WO42- or NO2- causes a shift of the pitting potential in the positive direction indicating the inhibition effect of added anions, while addition of NO3- anion accelerates the perchlorate pitting corrosion.

The anodic behaviour and corrosion of tin in various concentrations of isobutyric acid solutions has been studied by using cyclic voltammetry technique under different experimental conditions. The data reveal that the polarization curves are strongly pH dependent. It is clear that in the pH range from 2.4 to 4 no anodic peak appears. In the pH range from 5 to 6 only one anodic peak appears and the anodic peak current density (I-PA) in case pH 5 is greater than that in case pH 6. The anodic excursion spans of tin in isobutyric acid solution (pH 5) are characterized by the occurrence of a well-defined anodic peak (peak A), followed by a passive region. The passivation may be related to the formation and precipitation of oxide film on the electrode surface. The data reveal that increasing isobutyric acid concentration, temperature, and scan rate enhances the anodic peak current density (I-PA) and shifts its peak potential towards more positive values.Addition of some polyethylene glycols to the isobutyric acid solution (pH 5) decreases the current density of the anodic peak and shifts its peak potential towards the negative direction. These changes depend on the concentration and molecular weight of the polyethylene glycol added. (c) 2005 Elsevier B.V. All rights reserved.

The inhibition effect of ethoxylated fatty acids were used as inhibitors for the corrosion of zinc metal in 1.0M hydrochloric and 1.0M sulfuric acid solutions at various temperatures ranging from 25 to 55°C is investigated by weight loss measurement and electrochemical methods. The protection efficiency depends upon the type and concentration of the inhibitor and the nature of the acid medium. In both acid solutions the protection efficiencies of the inhibitors decrease with the increase in temperature. The inhibition was assumed to occur via the adsorption of the fatty acid molecules on the metal surface. The thermodynamic functions of dissolution and adsorption processes were calculated and discussed.

The electrochemical behaviour of Pb electrode in aqueous Na2SO4 solutions (pH=6.8) has been studied by means of cyclic voltammetric and potentiostatic current–time transient techniques. The anodic polarisation profiles exhibit three well defined peaks A1, A2 and A3 corresponding to the formation of PbSO4, PbO and PbO2, respectively prior to oxygen evolution potential. The reverse cathodic curves show three cathodic peaks C1–C3 and a plateau C4 prior to hydrogen evolution potential. The peak C1 is related to the reduction of upper PbO2 to PbSO4. The peak C2 is due to the reduction of the inner PbO2 to PbO. The composite peak C3 is due to the reduction of both PbO and PbSO4 to Pb. The plateau C4 is ascribed to the formation of PbH2. The heights of the anodic and cathodic peaks increase with increasing scan rate, temperature and repetitive cycling. The formation of PbSO4 layer proceeds under diffusion controlled of SO42−. The formation of the inner PbO is via a nucleation and growth mechanism under charge transfer and OH− diffusion control.

The inhibition of three ethoxylated fatty acids of different molecular weights on the corrosion of aluminum in both 1.0M HCl and 1.0M H2SO4 solutions have been studied at different temperatures (25–55°C) by means of weight loss and potentiodynamic polarization techniques. The inhibition efficiency for the three fatty acids increase with the increase in the inhibitors concentration but decreases with increasing temperature. The inhibition efficiency for the three inhibitors decreases in the order (n=20, 40, 80):OL[EO]80>OL[EO]40>OL[EO]20The inhibition occurs through adsorption of the inhibitor molecules on the metal surface without modifying the mechanism of corrosion process. Frumkin adsorption isotherms fit well the experimental data of dissolution and adsorption were calculated and discussed.

This paper describes the use of potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques in order to study the pitting corrosion susceptibility of a Zn electrode in KOH solutions containing KSCN as a pitting corrosion agent. Measurements were conducted under different experimental conditions. The results demonstrated that in the absence of KSCN, the anodic voltammetric response displays two anodic peaks prior to reaching the oxygen evolution potential. The first anodic peak A1 is related to the electroformation of Zn(OH)2. Peak A1 is followed by a wide passive region which extends up to the appearance of the second anodic peak A2. The latter is assigned to the formation of ZnO2. Addition of SCN− ions to the KOH solutions stimulates the anodic dissolution through peak A1 and breaks down the passive layer prior to peak A2. The breakdown potential decreases with an increase in SCN− concentration and temperature, but increases with an increase in KOH concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases slightly with increasing applied positive potential, SCN− concentration, and temperature.

The pitting corrosion behaviour of Zn in neutral (pH 6.8) Na2SO4 solutions was studied by using potentiodynamic and cyclic voltammetry techniques and complemented by X-ray analysis under the effect of electrolyte concentration, scan rate, temperature and pH. The voltammograms involve active/passive transition prior to the initiation of pitting corrosion. The active region displays one anodic peak. The passivity is due to the formation of ZnO film on the anode surface. The critical pitting potential decreases with increasing sulphate ion concentration and temperature but decreases with scan rate. Increasing the acidity or alkalinity of the medium enhances the pitting corrosion. The effects of adding increasing concentrations of Cr2O2−7, CrO2−4, WO2−4, MoO2−4 and NO−2 anions on sulphate pitting corrosion of Zn were investigated. These anions inhibit the active dissolution and pitting corrosion and the extent of inhibition depends upon the type and concentration of the inhibitors. The adsorption characteristics of these anions on the electrode surface plays a significant role in inhibition.

Sulphamethoxazole was tested as a corrosion inhibitor for mild steel in 1.0MHCl solution using potentiodynamic polarization and weight loss methods. The results showed that sulphamethoxazole is an effective inhibitor for mild steel in this medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. The protection efficiency increases with increasing inhibitor concentration (5×10−5 to 1×10−3M) but decreases with increasing temperature (30 to 60°C). The thermodynamic functions of dissolution and absorption processes were calculated.

The inhibition of the corrosion of mild steel in 1.0 M sulphuric acid solution by some ethoxylated fatty acids OL[EO]20, OL[EO]40 and OL[EO]80 has been studied in relation to the concentration of the inhibitors as well as the temperature using chemical (weight loss) and electrochemical (potentiodynamic polarization) techniques. The inhibition efficiency increases with increasing the concentration and the chain length of the inhibitor but decreases with temperature. The inhibition was assumed to occur via adsorption of the fatty acid molecules on the metal surface. The thermodynamic functions of dissolution and adsorption processes were calculated.