Portugaliae
Electrochimica Acta

Aluminum alloy corrosion behavior (AA6063) in a 0.5 M hydrochloric acid (HCl) solution was studied. It has been observed that the ethanolic extract of Cordia dichotoma seeds (EECdS) acts as an excellent inhibitor for AA6063 corrosion in a 0.5 M HCl solution. In this study, conventional weight loss, Fourier transformed infra-red spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) analysis techniques were used. It was found that the percentage inhibition efficiency increased with higher CdS concentrations. The thermodynamic and kinetic parameters, along with the equilibrium constant for the adsorption processes, showed that CdS performed well as an inhibitor. CdS adsorption on the alloy followed the Langmuir adsorption isotherm, at all the studied concentrations. FTIR, EIS and SEM investigations also indicated that CdS presence effectively lowered the dissolution currents.

N1,N2-Bis(1-Phenylethylidene)ethane-1,2-diamine (PEED) was tested as a corrosion inhibitor for C-steel in a 1.0 M HCl solution, by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed that PEED is a very good inhibitor, as its inhibition efficiency reached 93.8 %, with a concentration of 1.0x10-3 M, at 298 K. Tafel polarization study revealed that PEED acted as a mixed type inhibitor that obeyed Langmuir adsorption isotherm. The thermodynamic activation parameters for the corrosion reaction were calculated and discussed. Quantum chemical parameters and Fukui function were obtained by DMol3/GGA/PW91/DNP+ level of theory, which was performed using Materials Studiov 8.0 software from Biovia-Accelrys. Monte Carlo simulation was implemented to search for the equilibrium configurations of the PEED/Fe(111) adsorption system, in a 1.0 M hydrochloric acid solution.

Conducting polypyrrole was synthesized by the chemical oxidative method, and characterized using FTIR spectroscopy. An epoxy based paint containing conducting polypyrrole was prepared and applied on a low carbon steel sample, using a film applicator. The uncoated and painted steel samples were kept immersed in the simulated concrete pore solution. The Mott-Schottky technique was used to study the passive film formation on an uncoated low carbon steel, and the conducting polypyrrole coated low carbon steel was immersed in a simulated pore solution. The peaks at 1447 cm-1 and 1149 cm-1 are the responsible peaks of protonated nitrogen atoms in polypyrrole. The peak at 1538 cm-1 refers to the C-C stretching vibration in the pyrrole ring, and the peak at 1042 cm-1 denotes the C-H stretching vibration in the pyrrole ring. The M-S slope indicates that the passive film on uncoated low carbon steel exhibited n-type semi-conductive behaviour, and that the polypyrrole coating exhibited p- n type behaviour. However, with the increasing chloride contents and immersion time, the polypyrrole coating exhibited only p type behaviour.

The efficiency of Commelina benghalensis leaves extract as a mild steel corrosion inhibitor in hydrochloric acid (HCl) and sulphuric acid (H2SO4) has been evaluated. The corrosion rates were determined using the gravimetric (weight loss) and electrochemical techniques. The results obtained in the absence and presence of Commelina benghalensis extracts were used to calculate the inhibition efficiency (%), and to propose the inhibition mechanism and adsorption type. The obtained results showed that the inhibition efficiency increased with the increase in concentration of Commelina benghalensis extract. The phenomenon of chemical adsorption was proposed, and the inhibitor adsorption was found to obey Langmuir, Temkin and kinetic thermodynamic models. The polarization study reveals that, in the inhibitor presence, the corrosion current value decreases, indicating the formation of a protective film on the metal surface, which prevents the electron release from it.

The study of tropical fruits’ nutraceutical properties has been of great interest in the food research area. There are several parameters traditionally used to make fruits quality control, such as organoleptic analysis and physical and chemical assays. This work proposes the use of a simple, fast and low cost electrochemical technique for the characterization of fruit extracts in function of their ripening state, using as biological model a tropical fruit commonly named as Mortiño (Vaccinium meridionale swart). Cyclic voltammetry was selected as an electrochemical technique, due to the possibility of extracting kinetic and thermodynamic information from the results. A good correlation between the fruit extract’s physical-chemical properties and electrochemical parameters, such as peak intensity, charge and oxidation peak potential, was obtained.