On the relationship between corrosion inhibiting effect and molecular structure of 2,5-bis(<i>n</i>-pyridyl)-1,3,4-thiadiazole derivatives in acidic media: ac impedance and DFT studies

The inhibition properties of 2,5-bis(n-pyridyl)-1,3,4-thiadiazoles (n-PTH) on corrosion of mild steel in different acidic media (1 M HCl, 0.5 M H2SO4 and 1 M HClO4) were analyzed by electrochemical impedance spectroscopy (EIS). The n-PTH derivatives exhibit good inhibition properties in different acidic solutions and the calculated values of ΔG°ads revealed that the adsorption mechanism of n-PTH on steel surface is mainly due to chemisorption. While in 1 M HClO4, both 2-PTH and 4-PTH isomers stimulate the corrosion process especially at low concentrations. Quantum chemical calculations using the density functional theory (DFT) were performed on n-PTH derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that the inhibition effects of n-PTH may be explained in terms of electronic properties

Electrochemical and quantum chemical studies of new thiadiazole derivatives adsorption on mild steel in normal hydrochloric acid medium

In this work, a new class of thiadiazole derivatives, namely 3,5-bis(2-thienyl)-1,3,4-thiadiazole (2-TTH) and 3,5-bis(3-thienyl)-1,3,4-thiadiazole (3-TTH), have been studied as possible corrosion inhibitors for mild steel in molar hydrochloric acid (1 M HCl). Weight loss measurements, polarisation curves and AC impedance methods have been used. These studies have shown that the thiadiazole derivatives were very good inhibitors for mild steel in 1 M HCl. Comparison of results showed that 3-TTH was the best inhibitor. The potential of zero charge (PZC) of mild steel was studied by AC impedance method, and the mechanism of adsorption has been predicted. X-ray photoelectron spectroscopy surface analysis with thiadiazole derivatives shows that it chemisorbed at the mild steel/HCl interface. The adsorption of these inhibitors followed Langmuir's adsorption isotherm. The electronic properties of 2-TTH and 3-TTH, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR). These inhibitors are considered as non-cytotoxic substances

Enhanced corrosion resistance of mild steel in normal sulfuric acid medium by 2,5-bis(n-thienyl)-1,3,4-thiadiazoles: Electrochemical, X-ray photoelectron spectroscopy and theoretical studies.

International audienceEnhanced corrosion resistance of mild steel in normal sulfuric acid medium by 2,5-bis(n-thienyl)-1,3,4-thiadiazoles: Electrochemical, X-ray photoelectron spectroscopy and theoretical studies

Understanding the adsorption of 4 H -1,2,4-triazole derivatives on mild steel surface in molar hydrochloric acid

International audienceThis study examines the use of some 4H-triazole derivatives, namely 3,5-diphenyl-4H-1,2,4-triazole (DHT), 3,5-bis(4-pyridyl)-4H-1,2,4-triazole (4-PHT) and 3,5-bis(4-methyltiophenyl)-4H-1,2,4-triazole (4-MTHT) for corrosion and dissolution protection of mild steel in normal hydrochloric acid solution. The inhibiting efficiency of the different additives is evaluated by means of weight loss and electrochemical techniques such as ac impedance measurements and polarisation curves. The experimental results obtained reveal that 4-MTHT is the best effective inhibitor and the inhibition efficiency is found to be in the following order: 4-MTHT > 4-PHT > DHT. The variation in inhibitive efficiency mainly depends on the type and nature of the substituents present in the inhibitor molecule. Polarisation curves show that theses triazoles are mixed-type inhibitors in 1 M HCl. The inhibition efficiency increases with 4H-triazole derivatives concentration and attains the maximum value of 99.6% in the case of 4-MTHT at 5 × 10−4 M. The results obtained from weight loss electrochemical studies were in reasonable agreement. The adsorption of 4H-triazole derivatives on the steel surface obeys to the Langmuir isotherm model. The thermodynamic data of adsorption and activation are determined and discussed. The fundamental thermodynamic functions were used to glean important information about the 4H-triazoles inhibitory behaviour. Molecular modeling was used to get better insight, about structural and electronic effects in relation to the inhibition efficiencies

ac impedance, X-ray photoelectron spectroscopy and density functional theory studies of 3,5-bis(<i>n</i>-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbon steel surface in hydrochloric acid solution

The corrosion inhibition properties of a new class of oxadiazole derivatives, namely 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles (n-DPOX) for C38 carbon steel corrosion in 1 M HCl medium were analysed by electrochemical impedance spectroscopy (EIS). An adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The experimental results showed that these compounds are excellent inhibitors for the C38 steel corrosion in acid solution and that the protection efficiency increased with increasing the inhibitors concentration. Electrochemical impedance data demonstrate that the addition of the n-DPOX derivatives in the corrosive solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of an adsorbed layer over the steel surface. Adsorption of these inhibitors on the steel surface obeys to the Langmuir adsorption isotherm. X-ray photoelectron spectroscopy (XPS) and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal hydrochloric solution by n-DPOX is due to the formation of a chemisorbed film on the steel surface. Quantum chemical calculations using the Density Functional Theory (DFT) and the Quantitative Structure Activity Relationship (QSAR) approach were performed on n-DPOX derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that their inhibition effect is closely related to EHOMO, ELUMO, and dipole moment (μ)

Enhanced corrosion resistance of mild steel in molar hydrochloric acid solution by 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole: Electrochemical, theoretical and XPS studies.

The inhibition effect of the new pyridazine deriv., 1,4-bis(2-pyridyl)-5H-pyridazino[4,5-b]indole (PPI) against mild steel corrosion in 1 M HCl solns. was evaluated using weigh loss and electrochem. techniques (potentiodynamic polarization curves and impedance spectroscopy). Probably PPI is a good corrosion inhibitor and the inhibition efficiency increased with the increase of PPI concn., while the adsorption followed the Langmuir isotherm. XPS and theor. calcn. of electronic d. were carried out to establish the mechanism of corrosion inhibition of mild steel with PPI in 1 M HCl medium. The inhibition action of this compd. was, assumed to occur via adsorption on the steel surface through the active centers contained of the mol. The corrosion inhibition is due to the formation of a chemisorbed film on the steel surface

Improvement of corrosion resistance of carbon steel in hydrochloric acid medium by 3,6-bis(3-pyridyl)pyridazine

Corrosion inhibition of carbon steel in normal hydrochloric acid solution at 30°C by new pirydazine derivative, namely 3,6-bis(3-pyridyl) pyridazine (3-PYP) has been studied by a series of known techniques such as weight loss, polarisation and electrochemical impedance spectroscopy (EIS). The experimental results have showed that this organic compound revealed a good corrosion inhibition and that the inhibition efficiency is increased with the inhibitor concentration. Potentiodynamic polarisation suggested that it is a mixed type of inhibitor. Two time constants determined by the charge-transfer and the adsorption of the inhibitor, respectively, can be readily outlined. The adsorption of 3-PYP on the carbon steel surface, in 1 M HCl solution, obeyed to the Temkin's isotherm with a very high negative value of the standard Gibbs free energy of adsorption δG°ads (chemisorption). Quantum chemical calculations and X-ray photoelectron spectroscopy (XPS) analysis were carried out to establish the mechanism of corrosion inhibition of carbon steel in 1 M HCl medium in the presence of 3,6-bis(3-pyridyl)pyridazine (3-PYP)