Portugaliae
Electrochimica Acta

This study investigated one of the chemical compounds taken by diabetic patients as a replacement for natural sugar. Its aim was to identify the electrochemical properties of sodium saccharin in different electrolytes, using a nano-sensor. Sodium saccharine was studied by cyclic voltammetric technique, in different electrolytes, using a modified glassy carbon electrode (GCE) with carbon nanotubes (CNT) as working electrode (CNT/GCE). It was found that the redox current peaks of 0.01 mM sodium saccharine in 1 M Na2SO3 enhanced both redox peaks with the CNT electro-catalyst on the GCE surface. Different concentrations, pH and scan rates of sodium saccharine in Na2SO3 have been studied. Also, the nano sensor showed good reliability and stability towards the chemical compounds in the cyclic voltammetric cell. Other electrochemical parameters were determined, such as the potential peak separation (Epa-Epc≈100 mV), the current ratio (Ipa/Ipc≈1) of the redox peaks and the cathodic-anodic reaction rate. The diffusion coefficient value was determined at different scan rates.

Environmental green compounds have emerged as powerful inhibitors for metals and alloys corrosion. So, this article attempts to show that barbituric (BA) and thiobarbituric acids (TBA) are good green corrosion inhibitors for copper immersed in 0.6 mol/L NaCl. A combination of quantitative and qualitative tools were used in this investigation, such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Polarization measurements indicate that these compounds can function as mixed type inhibitors. It was found that the adsorption of these inhibitors onto the copper surface obeyed Flory-Huggins isotherm. Also, the effect of temperature in the inhibitors absence and presence was studied according to Arrhenius isotherm. Some thermodynamic functions of dissolution and adsorption processes were calculated, such as activation energy (Ea), enthalpy (ΔH*), free energy (ΔGo) and entropy (ΔS*). The barbituric and thiobarbituric acids recorded high inhibition efficiency of copper corrosion at concentrations of 5x10-3 mol/L and 1x10-3 mol/L, respectively.

The corrosion inhibition effect of ethanol extract of Acacia nilotica leaves (ANLE) on mild steel in 0.1 M H2SO4, containing 0.1-0.5 g/L, has been studied using weight loss, Potentiodynamic Polarization (PDP), Fourier Transforms Infra-Red (FTIR) spectroscopy, UV-visible spectroscopy, High-Performance Liquid Chromatography (HPLC) and Scanning Electron Microscopy (SEM) methods. The results from weight loss and PDP show that the inhibition efficiency depends on the concentration of the plant extract, as well as on the time of exposure of the mild steel samples in H2SO4 solutions. The optimum inhibition efficiencies of the extract obtained from weight loss and potentiodynamic measurements were found to be 87.57% and 61.85%, respectively. Thermodynamic parameters, such as Ea, ΔH, ΔG and ΔS, were evaluated at 0.5 g/L, and the results were found to be -78.54 kJ/mol, 74.66 kJ/mol., -17.92 kJ/mol and -90.59 kJ/mol, respectively. From the calculated values of activation energy and free energy of adsorption, and from the trend in the variation of inhibition efficiency with temperature, the inhibitor mechanism of adsorption was found to be physical adsorption, exothermic, spontaneous, being best described by Langmuir adsorption model, because the regression coefficients (R2) values calculated from the plots were closest to unity, confirming a highest degree of linearity. Mild steel surface morphology, in ANLE presence and absence, was studied using SEM. FTIR spectroscopy and UV-visible spectroscopy analyses were used to confirm the adsorption process onto the metal surface. Spectra analysis obtained from FTIR study indicated that ANLE was adsorbed onto the mild steel surface via C-O and N=O functional groups. HPLC was also used to find the main component responsible for inhibition, at 5.990 min, which was Catechin. The obtained results revealed that ANLE acts as a good inhibitor and could serve as an effective mild steel corrosion inhibitor in a 0.1 M H2SO4 solution.

This work is a contribution to the study about the inhibition of mild steel corrosion in a molar hydrochloric acid medium by some benzoxazol derivatives compounds. The study was carried out using gravimetric and electrochemical methods (stationary and transient). We have considered the influence of the inhibitor concentration, the temperature of the medium and the duration of the immersion of the metal sample in the aggressive medium. These studies are complemented with theoretical calculations aimed to correlate the results obtained from experimental measurements using the DFT method. The results obtained in this work through gravimetric and both transient and stationary electrochemical methods showed a satisfied coherence. Theoretical calculations also revealed a good correlation with the experimental results for our compounds.

The inhibition effect of Cefalexin on mild steel corrosion in sodium chloride has been examined with the use of electrochemical potentiodynamic polarization techniques, weight loss measurements and computational studies. Cefalexin showed good protection ability by adsorbing onto the mild steel surface. The mixed inhibition characteristics of Cefalexin were revealed by the potentiodynamic polarization results. The inhibitor efficiency was found to be above 65%, obeying the Langmuir and Freundlich isotherm law, with a correlation regression coefficient of R2= 0.9984 and R2= 0.9488, respectively, establishing the reliability on Cefalexin as an inhibitor.