Polyphosphate derivatives of guanidine and urea copolymer: Inhibiting corrosion effect of Armco iron in acid solution and antibacterial activity

A new corrosion inhibitor, namely, polyphosphate derivative of guanidine and urea copolymer (PGUC) has been synthesised and its inhibiting action on the corrosion of Armco iron in molar hydrochloric acid (1 M HCl) has been investigated at 30 °C using electrochemical impedance spectroscopy method (EIS). Data obtained from EIS measurements were analysed to model the corrosion inhibition process through appropriate equivalent circuit model. The experimental results revealed that PGUC is an efficient inhibitor and the inhibition efficiency increases with increase in inhibitor concentration, reaching value up to 91% at a concentration of 11.5 g/l. Adsorption of PGUC on the Armco iron surface in 1 M HCl solution follows Temkin’s isotherm. The low negative value of the standard free energy of adsorption, , indicates the physical nature of adsorption (physisorption) of PGUC. The inhibition mechanism of PGUC was discussed. This inhibitor can be used as biocides in aqueous environments. The results showed also that the PGUC has a broad inhibitory spectrum against both Gram positive and Gram negative bacteria. The MIC measured for Staphylococcus aureus was of ca 6-fold lower than the efficient inhibitory corrosion concentration of PGUC (11.5 g/l). However, the MICs measured for Escherichia coli and Pseudomonas aeruginosa were of ca 2.7-fold and of ca 10.9 higher than this concentration.     

A stabilized meshfree reproducing kernel‐based method for convection–diffusion problems

In this paper, we develop a meshfree particle‐based method for convection–diffusion problems. Discretization is performed by using piecewise constant kernels. The stabilized scheme is based on a new upwind kernel. We show that accurate and stable scheme can be obtained by using purpose‐built kernels. It also shown that under some conditions the classical optimal finite difference scheme can be derived by the new method. Several numerical tests validate the method. Copyright © 2011 John Wiley & Sons, Ltd.     

The inhibition of mild steel corrosion in acidic solutions by 2,5-bis(4-pyridyl)-1,3,4-thiadiazole: Structure-activity correlation

The effect of 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (4-PTH) on the corrosion of mild steel in acidic media (1 M HCl, 0.5 M H₂SO₄, 1 M HClO₄) has been investigated using weight loss measurements, electrochemical impedance spectroscopy and potentiodynamic polarisation. These studies have shown that 2,5-bis(4-pyridyl)-1,3,4-thiadiazole is good inhibitor for mild steel in 1 M HCl, 0.5 M H₂SO₄ and 1 M HClO₄ solutions, the better performances are seen in the case of 1 M HCl solutions. But in 1 M HClO₄, the 4-PTH stimulates corrosion at low concentrations. Polarisation curves indicate that the 4-PTH is a mixed-type inhibitor in all acidic media and E (%) is temperature-dependent. Adsorption on the mild steel surface follows the Langmuir isotherm model in all acidic media. The electronic properties obtained using the Hartree-Fock AB initio 3-21G quantum chemical approach, were correlated with the experimental efficiencies.     

Thermodynamic characterization of metal dissolution and inhibitor adsorption processes in mild steel/2,5-bis(n-thienyl)-1,3,4-thiadiazoles/hydrochloric acid system

The corrosion inhibition of mild steel in 1 M hydrochloric acid solution by some 2,5-bis(n-thienyl)-1,3,4-thiadiazoles (n-TTH) has been studied in relation to the concentration of the inhibitors as well as the temperature using chemical (weight loss) and electrochemical (ac impedance and dc polarisation) techniques. All the methods employed are in reasonable agreement. The protection efficiency increases with increasing inhibitors concentration and with increasing temperature. The thermodynamic functions of dissolution and adsorption processes were calculated from experimental polarisation data and the interpretation of the results are given. Adsorption of n-TTH was found to follow the Langmuir’s adsorption isotherm and the ability of the molecule to chemisorb on the steel surface was dependent on the position of the sulphur atom on the thienyl substituent.     

Corrosion protection of galvanized steel and electroplating steel by decanoïc acid in aqueous solution: Electrochemical impedance spectroscopy, XPS and ATR-FTIR

The inhibiting action of decanoïc acid towards the corrosion behaviour of galvanized steel and electroplating steel in aqueous solution has been studied using electrochemical impedance spectroscopy (EIS) techniques. Data obtained from EIS show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Results obtained revealed that decanoïc acid is an effective inhibitor. The better performance was obtained in the case of electroplating steel. X-ray photoelectron spectroscopy surface analysis shows that, decanoïc acid is chemisorbed on surface of galvanized steel and electroplating steel. These studies have shown that the active site for binding the film on metal surface is the anionic carboxylate head. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to identify the nature of the deposits on the metal surface.     

Corrosion inhibition of carbon steel and antibacterial properties of aminotris-(methylenephosphonic) acid

In this work, the corrosion inhibition property and the antibacterial activity of the aminotris-(methylenephosphonic) acid (ATMP) have been studied. ATMP has been evaluated as a corrosion inhibitor for carbon steel in 1 M HCl solution using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. According to the experimental results, the inhibition efficiency increased with increasing inhibitor concentration. Tafel polarization study showed that the ATMP acts as a mixed inhibitor. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. Adsorption of ATMP on the carbon steel surface obeyed the Langmuir adsorption isotherm. The calculated ΔG_ads value showed that the corrosion inhibition of the carbon steel in 1 M HCl is mainly controlled by a physisorption process. In addition, the effect of immersion time on the corrosion of carbon steel was also studied in this work using ac impedance technique. The corrosion inhibition mechanism of ATMP was discussed. This inhibitor can be also used as biocide in aqueous environments. Our results showed that ATMP have an antibacterial effect against both Gram positive and Gram negative bacteria. The lowest MIC (0.2 mg l^?1) was measured for Pseudomonas fluorescens while the highest MIC was measured for Escherichia coli (3.1 mg l^?1). In addition, the results showed that the MIC of ATMP against Listeria innocua in a buffered medium (pH 6.5) was of ca. 4-fold higher than MIC measured in unbuffered medium. Thus, our findings showed that the antibacterial activity of ATMP is a result of a combined effect of the pH solution and the chemical nature of the used phosphonate molecule.     

Electrochemical and quantum chemical studies of some indole derivatives as corrosion inhibitors for C38 steel in molar hydrochloric acid

A comparative study of 9H-pyrido[3,4-b]indole (norharmane) and 1-methyl-9H-pyrido[3,4-b]indole (harmane) as inhibitors for C38 steel corrosion in 1 M HCl solution at 25 °C was carried out. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behavior in the absence and presence of different concentrations of these inhibitors. The OCP as a function of time were also established. Cathodic and anodic polarization curves show that norharmane and harmane are a mixed-type inhibitors. Adsorption of indole derivatives on the C38 steel surface, in 1 M HCl solution, follows the Langmuir adsorption isotherm model. The values were calculated and discussed. The potential of zero charge (PZC) of the C38 steel in inhibited solution was studied by the EIS method, and a mechanism for the adsorption process was proposed. Raman spectroscopy confirmed that indole molecules strongly adsorbed onto the steel surface. The electronic properties of indole derivates, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR).     

Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole in normal hydrochloric acid medium

The inhibition performance of the 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (4-MAT) on mild steel in normal hydrochloric acid medium (1 M HCl) at 30 °C was tested by weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. This organic compound inhibits the acidic corrosion even at very low concentration, reaching a value of inhibition efficiency up to 98% at a concentration of 3 × 10⁻⁴ M. The results obtained from the different corrosion evaluation techniques are in good agreement. Polarisation curves indicate that 4-MAT is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit model, a constant phase element (CPE) has been used. The adsorption of 4-MAT on the steel surface, in 1 M HCl solution, obeys to Langmuir’s isotherm with a very high negative value of the free energy of adsorption ΔG°_ads (chemisorption). X-ray photoelectron spectroscopy (XPS) was carried out to establish the mechanism of corrosion inhibition of mild steel in 1 M HCl medium in the presence of 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (4-MAT).