Portugaliae
Electrochimica Acta

The ability of benzyl nicotinate (BN) to inhibit the corrosion process of cold rolled steel (CRS) in a 1 M HCl solution has been investigated by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic methods. The potentiodynamic polarization study revealed that BN acts as a mixed type inhibitor. The effect of temperature range (303-333 K) on the corrosion of steel was studied at different concentrations of BN. The efficiency of this inhibitor increases with an increase in its concentration, and decreases with rise of temperature. Free energy values revealed that BN molecule undergoes comprehensive adsorption. The adsorptive behavior of BN on CRS obeys Langmuir adsorption. The thermodynamic and activation parameters calculation helped in getting insight into the inhibitor mechanism. The DFT (density functional theory) studies of BN molecule also supported our experimental findings.

In the present work, the electrochemical oxidation of acid orange 7 (AO7) on a glassy carbon (GC) electrode has been investigated by cyclic voltammetry in different solvents: aqueous solvent (H2O), dimethyl sulfoxide (DMSO) and acetone (ACE), using sulfuric acid as a supporting electrolyte. The analysis of AO7 oxidation voltammograms in different solvents showed that the more donor numbers, the easier it becomes the oxidation of AO7. The experimental parameters show that the oxidation peak current of AO7 was linearly proportional to its concentration in a range from 0.04 mM to 0.2 mM. The limit of detection was estimated by gradually decreasing the concentration levels of AO7, and was found to be 6.6 µM.

The corrosion inhibition of aluminum by the extract of Trigonellafoenum-graecum L was studied in a hydrochloric acid 1 M solution using electrochemical polarization measurements and electrochemical impedance spectroscopy (EIS). Three organic solvents, pentane, dichloromethane (DCM) and ethanol, of different polarities, were tested. An inhibition efficiency of 86.6 %, 84.41 %, and 75.77 % was obtained by the addition of 1400 ppm of the extract using three solvents: DCM, ethanol and pentane, respectively. The potentiodynamic curves show that the decrease of aluminum corrosion in the presence of the fenugreek extract in a HCl 1 M solution mainly acts by a mixed process with an anodic tendency for both extracts with ethanol and with pentane; on the other hand, the extract with DCM showed a cathodic tendency. The temperature effect on the corrosion of aluminum indicates that the inhibition efficiency of the natural substance decreases with an increase in temperature. The inhibition efficiency values obtained from the polarization curves are in good agreement with those of EIS.

The need to improve the structural properties of materials in petrochemical industry, due to recurring failure, has motivated this study. The effect of deposition potential on structural integrity, surface topography and micromechanical progression of Zn based induced aluminium and TiO2 alloy coating series on mild steel was studied. The wear stability and microhardness behaviour of the developed composite coating was examined via, respectively, sliding reciprocating rig and dura scan diamond based microhardness tester. The structural reliability was inspected with scanning electron microscope equipped with EDS, and atomic force microscope. The results showed that the superb structural crystal resulted into a significant increase in the microhardness, and into a decrease in wear plastic deformation in a non-lubricated system. The precipitation of the deposits enforces stable crystal orientation and compact grains growth. The work has established that up to 13wt% TiO2 on zinc rich bath, a solid composite coating on mild steel, can be used to improve the service life of coating for stable structural properties.

The electrochemical behavior of pramipexole dihydrochloride was studied at carbon paste electrodes in 0.04 M Britton–Robinson buffer of pH 6.08, using cyclic and differential pulse voltammetric techniques. The oxidation of pramipexole dihydrochloride is an irreversible diffusion-controlled process. A differential pulse anodic voltammetric procedure has been developed for determination of the drug over the concentration range of 1.20 – 8.23 μg/mL, with detection and quantification limits of 0.21 and 0.68 μg/mL, respectively. The proposed method was successfully applied for the determination of the drug in its commercial tablets.