Portugaliae
Electrochimica Acta

The electrochemical behaviour of nicotine extracted from commercial cigarette tobacco were studied in a blood media, at a glassy carbon electrode (GCE), using cyclic voltammetry technique. The nicotine compound oxidized the blood component in neutral media, at pH 7.4. The response was evaluated with respect to different pH values, scan rates, concentrations and temperatures. From the voltammogram of nicotine in a blood medium, it was found that the oxidation current peak of nicotine was +999 mV in acidic and alkaline media, which enhanced about twice in an acidic medium and disappeared in an alkaline medium. In its turn, at highly acidic media, three reduction current peaks appeared in the nicotine voltammogram in blood media. The electrochemical behavior of nicotine was investigated using cyclic voltammetry technique; the method was successfully applied for the determination of the nicotine compound which had a reversible redox couple in a blood medium from the peak potential separation of 100 mV. Also, it was found that the average value of the diffusion coefficient at the cathodic electrode was 4.075x1011 cm-2 s-1, and 22.625x1011 cm-2 s-1 at the anodic electrode.

The present work highlights the results of the application of a green inhibitor for material conservation. The anticorrosive performance of the pectin bio-polymer was established for the corrosion control of mild steel in a 1 M phosphoric acid medium. Electrochemical measurements such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) studies were adopted for the corrosion inhibition studies. The studies were carried out by varying the concentrations of pectin in the temperature range from 303 K to 318 K. Conditions were optimized to get maximum inhibition efficiency. The surface morphology study was done by scanning electron microscope (SEM), and elemental mapping was done using energy dispersive X-ray (EDX) studies to confirm the adsorption and interaction of the inhibitor with the material. Studies showed an increase in the inhibition efficiency with an increase in the concentration of pectin and also in the temperature. Maximum inhibition efficiency of 70% was achieved by the addition of 800 ppm of inhibitor. Pectin acted as a mixed type inhibitor by bringing down both cathodic and anodic reactions. Kinetic and thermodynamic parameters revealed chemical adsorption of pectin onto the mild steel surface. A suitable mechanism was proposed for the adsorption of pectin which was reaffirmed by the surface morphology studies. Pectin emerged as a potential eco-friendly green inhibitor for the corrosion control of mild steel, with economic benefits.

An irreversible electrode reaction influenced by the reversible potential dependent inhibition is theoretically analysed. The consequence of reactivation of the electrode surface is the continuation of electro-oxidation and the appearance of the second anodic peak in cyclic voltammetry. An indicator of the change of the electrode kinetics caused by the inhibitor is proposed.

In the present paper, the methanol extract from the leaves of Pistacia terebinthus L. (PT) was characterized by GC/MS analysis. It was tested as a corrosion inhibitor for iron in a 3% NaCl solution, using gravimetric measurements and electrochemical methods (potentiodynamic polarizations and electrochemical impedance spectroscopy). Fourteen compounds were identified; the major compounds are palmitic acid (31.5%), stearic acid (25.7%) and oleic acid (11.3%). The data showed that the tested extract offers good corrosion resistance. The constituents of the PT extract affected polarization resistance (Rp) and corrosion current density (icorr), demonstrating that the proposed inhibitor hinders corrosion reactions. The results obtained at 200 ppm are very interesting, and reach maximum values of 96.96%, 89% and 64.82%, respectively, which were confirmed by scanning electron microscopy (SEM), coupled with energy scattering of X-ray spectroscopy (EDX).

Electrochemical methods for the recycling of tungsten carbide (WC-10Co) resources suffer from passivation in the acidic medium caused by WO3 and also in NaOH electrolytes, due to hydroxide formation. We found that an ammoniacal solution is a promising electrolyte for sustainable electrochemical dissolution of both tungsten (W) and cobalt (Co). The ammoniacal medium performs greatly when supported with Cl-, SO42- and CO32- ions. Poor dissolution/corrosion tendency of WC-10Co in a diluted NH4OH solution enhanced many folds in the presence of Cl-, SO42- and CO32- ions. Among these supporting ions, Cl- emerged as the most suitable for the electrochemical leaching of W and Co from the WC-10Co, accompanying the least noble behavior of WC-10Co. An electrolyte composed of 150 g/L of ammonia and 5% (w/v) of NH4Cl yielded the maximum anodic current density. Microscopic examination of the electrochemically treated samples shows scattered active sites responsible for the oxidative dissolution of WC-10Co. The usefulness of W and Co dissolution in ammonia-additive salt followed the order NH4OH-NH4Cl>NH4OH-(NH4)2SO4>NH4OH-(NH4)2CO3.