Portugaliae
Electrochimica Acta

The inhibition effect of Thymus willdenowii Boiss & Reut essential oil (TW) on the mild steel corrosion in 1 M HCl has been investigated using weight loss measurements, surface analysis (SEM-EDX, three-dimensional profilometry and FT-IR), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The TW oil anticorrosion effect was evaluated using polarization potentiodynamic curves obtained after 30, 60 and 90 min of immersion in a 1 M HCl medium. Gravimetric results have shown that TW oil has a significant inhibition efficiency value of 81.42%, which was attained at 3 g/L. The polarization measurements have shown that TW is a mixed type inhibitor, with a significant reduction in cathodic and anodic current densities. Measurements by electrochemical impedance spectroscopy revealed that resistance to the charge transfer has increased with higher TW oil concentrations. From the use of SEM-EDX and three-dimensional profilometry, it is clear that the metal surface has remarkably improved in the TW oil presence, compared to the one exposed to the acid medium without essential oil. From the TW proprieties and the obtained results, it can be concluded that this oil is a new natural substance that can be used against material corrosion in aggressive solutions.

Stearalkonium chloride (SAC) ultrasonic velocity has been measured in methanol, at 301 K temperature. Jacobson’s model has been used to evaluate adiabatic and molar compressibility, molar sound velocity, solvation number, relative association, relaxation strength and other acoustical constants. The results of ultrasonic measurements of different SAC solutions in methanol indicate that there is a signification interaction between SAC and methanol molecules in diluted solutions. The conductometric study indicates that SAC behaves as a weak electrolyte in methanol. The thermodynamic constants calculated from conductance measurements for SAC solutions in methanol depict that micellization is favored over dissociation processes. The refractive index variation with SAC solutions concentrations shows a marked change in the refractive index value at critical micelle concentrations (CMC). Data treatment of obtained ultrasonic velocity, conductance measurement and refractive index shows that there is significant interaction between SAC and methanol molecules in diluted solutions, and that SAC molecules do not aggregate appreciably below the CMC.

Ethyl 3-hydroxy-2-(p-tolyl)-3,4-dihydro-2H-benzo[b][1,4]thiazine-3-carboxylate (EHBT) inhibition effect and its adsorption onto a mild steel surface in phosphoric acid (2 M H3PO4) was investigated, at temperatures varying between 298 and 328 K, by weight loss, EIS and potentiodynamic polarization techniques. The tested compound showed an inhibition efficiency that was superior to 88 % for a concentration equal to 5 × 10-3 M. Polarization measurements indicated that the examined EHBT acted as a mixed inhibitor. The protection efficiency increased with higher inhibitor concentrations and decreased with an increase in temperature. EHBT adsorption onto the mild steel surface obeyed Langmuir adsorption isotherm. EHBT inhibition action was also evaluated by surface SEM images.

Polypyrrole (PPy) films were electrochemically synthesized on an Au/TiO2 coated quartz crystal electrode in solutions with different heparin (Hep) concentrations. The PPy films morphology was determined by tapping a mode atomic force microscopy (AFM). The influence of the dopant concentration on the coating surface roughness was studied. Electrochemical quartz crystal microbalance (EQCM) results suggest that Hep retained in the PPy films was bound to thrombin. The adsorbed thrombin amount increased with a higher coating surface roughness. PPy films doped with Hep are electroactive and show cation exchange properties under oxidation or reduction conditions in a Ringer solution. The pre-oxidized PPy film adsorbed a greater thrombin amount than the freshly one and even more than the pre-reduced film.

An ionic liquid (IL) based pencil graphite electrode (PGE) sensor was electrochemically fabricated for hydroquinone (HQ), catechol (CC) and resorcinol (RS) simultaneous detection and estimation in aqueous media. PGE surface was modified by 1-hexylpyridinium hexafluorophosphate (HPHP) using cyclic voltammetry (CV). The modified surface was characterized by scanning electron microscope (SEM) and energy dispersive X-ray microanalysis (EDX). The modified electrode showed an excellent electro-analytical activity towards simultaneously HQ, CC and RS, at pH 6.8 in aqueous media. The scan rate effect was diffusion controlled and the concentration effect was linear with current. The limit of detection (LOD) for HQ, CC and RS was found to be 6.38 μmol L¹, 4.56 μmol L¹ and 19.6 μmol L¹, respectively. The sensitivity for HQ, CC and RS was found to be 448.49 μAmM-1cm-2, 627.35 μAmM-1cm-2 and 146.10 μAmM−1cm−2, respectively, in a ternary mixture of dihydroxybenzene isomers (DHBIs). The cost of using PGE was lower than that of the conventional electrodes