Portugaliae
Electrochimica Acta

Carbonaceous materials are used to generate composites for numerous purposes, due to their extraordinary properties. In this context, we have carried out a study on the modified properties, viz. thermal stability and specific capacitance of the composites fabricated by the introduction of a carbonaceous material (graphite and graphene oxide) into the Polyvinyl Butyral matrix. Since it has excellent adhesibility and dielectric permittivity, and it can be employed as an electrode in sensors, polyvinyl butyral is used in the current investigation, along with carbonaceous materials, for electrochemical and bandgap properties (HOMO-LUMO) studies. Spectroscopic FT-IR, XRD and SEM analyses remark the comprehensive entanglement of the two components. Various fabricated composites show an increased thermal stability, with a percentage of carbonaceous filler, as suggested by TGA. Cyclic voltammetry studies reveal that PVB acts as an excellent binder, and as a good matrix for the charge movement through it, because it has a good level of dielectric permittivity, thus enabling fabricated materials to be developed as good candidates for supercapacitive batteries

The electrochemical degradability of Al-20% Mg and hypereutectic Al-22% Si industrial alloys was evaluated in an aggressive acidic environment, namely 1 M H2SO4, using potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. The microstructure and constituting phases of the surface alloys were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), coupled with Energy Dispersive X-ray Spectroscopy (EDX). It was found that the two alloys’ corrosion behavior mainly depends on their crystalline phases. The presence of the active intermetallic β- Al3Mg2 phase in the Al alloy with high Mg content induced a preferential Mg dissolution, which caused a severe intergranular attack on this alloy by the corrosive solution. Meanwhile, the Al alloy containing high Si content, which presented the eutectic Al-Si phase, showed a uniform and weaker dissolution. It was also observed that a rise in temperature reduced the corrosion performance of the two studied alloys, as these corroded faster than pure aluminum.

Use of Amaranthus extract, as mild steel corrosion inhibitor, in a pickling paste with H2SO4, has been investigated. The electrochemical experiments were conducted to bring forth results regarding various parameters, viz., corrosion current, anodic polarization and cathodic polarization. The corrosion current gradually decreased with time, for both uninhibited and inhibited systems. Polarization curves values indicate that Amaranthus extract adsorption modified anodic dissolution mechanism, as well as cathodic hydrogen evolution. From the results, it is clear that both cathodic and anodic reactions were inhibited, and that inhibition increased as the inhibitor concentration increased in acidic media, but the cathode was more polarized. This result indicated that Amaranthus extract can be classified as a cathodic inhibitor, in a 4 N H2SO4 solution. Surface analysis via scanning electron microscope (SEM) showed a significant improvement on the mild steel plate surface morphology, in the presence of optimum inhibitor concentrations. Thus, by conducting these experiments, our aim is to use inhibited pickling acid in the paste form, so that it can be conveniently applied on large structures, as well as on small tools, to be pickled/cleaned. As a contribution to the current interest on environmentally friendly green corrosion inhibitors, the present study investigates the inhibiting effect of Amaranthus extract, a green inhibitor which is commonly known as Pigweed.

The non-toxic anticorrosion properties of nicotinamide have been studied on aluminum in an acidic medium. The techniques included weight loss method, electrochemical measurements, quantum chemical calculations, Monte Carlo simulation, infra-red spectroscopy and scanning electron microscopy. This study gathers information about the inhibitor molecule adsorption onto the surface of metal specimens. Thermodynamic parameters were utilized to predict the adsorption mechanism. The dependence of corrosion inhibition efficiency on various parameters was examined, and it was seen that the increase in the inhibitor concentration and in temperature led to an increase in the inhibition efficiency. The dipole moment and EHOMO-ELUMO influenced the inhibition efficiency, which was observed by quantum chemical studies.

In this work we made a synthesis of two molecules of the same family, the pyrazole 4-(4,5-dihydro-1H-pyrazol-5-yl)-N,N-dimethylaniline D and N,N-dimethyl-4-(3-methyl-4,5-dihydro-1H-pyrazol-5-yl)aniline D10. These two molecules have a good inhibiting activity against the corrosion of mild steel in 1 M HCl. This activity has been confirmed by gravimetric and electrochemical studies; we use a potentiodynamic polarization and the impedance spectroscopic technique. From this investigation, we observe that the integration of a methyl group in the pyrazole D allows decreasing slightly the corrosion of steel. For more information about the action mode of our inhibitors, we launched theoretical calculation by DFT method. We used these calculations to discuss the stability, the reactivity, and the adsorption of our pyrazolic inhibitors with iron in acid medium.