Portugaliae
Electrochimica Acta

The inhibition efficiency of sodium dodecyl sulfate (SDS) in controlling corrosion of carbon steel in aqueous solution containing 120 ppm of Cl− in the presence and absence of Zn2+ has been evaluated by weight loss method. The formulation consisting of 300 ppm of SDS and 75 ppm of Zn2+ gives 93 % inhibition efficiency. A synergistic effect exists between SDS and Zn2+. As the immersion period increases, the inhibition efficiency of SDS-Zn2+ decreases. Polarization study reveals that this formulation controls both the anodic and cathodic reactions. AC impedance spectra reveal that a protective film is formed on the metal surface.

Inhibition of the corrosion of zinc in 0.01 to 0.0 4 M H2SO4 by erythromycin was studied using weight loss and hydrogen evolution methods. The results obtained indicate that erythromycin is a good adsorption inhibitor for the corrosion of zinc in H2SO4 solutions. The inhibition efficiency of erythromycin increases with increasing concentration but decreases with increase in temperature. Thermodynamic and adsorption studies reveal that the adsorption of erythromycin on zinc surface is exothermic, spontaneous and is characterised with increasing degree of orderliness. The adsorption characteristics of the inhibitor are best described by the Langmuir adsorption model. From the variation of inhibition efficiency with temperature and the calculated values of the activation and free energies (which are within the limits expected for physical adsorption), we propose that the adsorption of erythromycin on zinc surface is consistent with the mechanism of physical adsorption.

Myeloperoxidase (MPO) is a neutrophil enzyme that employs hydrogen peroxide (H2O2) to catalyze the oxidation of halides and thiocyanate to their respective hypohalous acids. In this study, the inhibitory effect of nitrite (NO2-) on MPO-catalytic activity was investigated electrochemically. H2O2 consumption during steady-state catalysis was monitored amperometrically by a carbon fiber based H2O2-biosensor at 25 oC. Optimized initial concentrations were 50 nM MPO, 10 μM H2O2, and a selected halide or thiocyanate concentration from physiological range. Under these conditions, reactions were monophasic and rapid (complete H2O2 consumption occurs in < 10 s). As concentration of NO2- increases, reactions change to biphasic (rapid step followed by a slow step) and both steps have been inhibited by NO2-. Our results confirmed the inhibitory effect of NO2- and demonstrated for the first time that NO2- is a strong inhibitor towards MPO-catalyzed oxidation of iodide and bromide; and a weak inhibitor towards MPO-catalyzed oxidation of chloride and thiocyanate.

Surface modification by chitosan (CT) on a glassy carbon electrode (GCE) was employed in the present study to determine metal traces (Cu, Pb, Cd, Co, As and Pt). Previous report about the chitosan film affinity toward positive or negative species demonstrated and allowed the application of these polymeric films for detecting heavy metals in aqueous solutions. The modified surface exhibited an affinity to chelating metal ions in solution, forming complexes. Differential pulse voltammetry combined with a pre-concentrating process and standard addition method were employed for trace analysis, obtaining the detection ranges (Cu (II) from 3.99E-6 to 3.91E-5 mol L-1, Pb(II) from 1.99E-6 to 1.58E-5 mol L-1, Cd(II) from 1.59E-5 to 6.23E-5 mol L-1, As(IV) from 7.99E-6 to 5.04E-5 mol L-1, Pt(IV) from 8.19E-6 to 3.59E-5 mol L-1, Co(II) from 6.11E-4 to 2.78E-3 mol L-1), calibrations plots and relevant equations for each metal. Finally, cyclic voltammetry technique was used to characterize the polymeric surface behavior in presence of different metals and during the differential pulse voltammetric analysis. The results are described and discussed in the light of the existing literature.

The inhibition of copper corrosion in 3.5% NaCl solution has been studied at 25 oC using three inhibitors: 1-phenyl-2,4-dithiobiuret(Inh I), 1-p-methoxyphenyl-2,4-dithiobiuret(Inh II) and 1-p-chlorophenyl-2,4-dithiobiuret(Inh III). The inhibition efficiencies of these compounds have been evaluated by weight loss and electrochemical methods (impedance spectroscopy and polarisation curves). The surface study was done by using SEM and ESCA techniques. The inhibition efficiencies of the inhibitors follow the sequence Inh II > Inh I > Inh III. The inhibitors Inh I, Inh II and Inh III appear to inhibit corrosion process through the formation of a protective film which was found to consist of Cu(I)-inhibitor complex, cuprous chloride CuCl or CuCl2- complex ions or both on the surface.

Optical, electrochemical and spectroelectrochemical features of a family of triisopropylsilyl (TIPS) end-capped oligothienoacenes from the tetramer to the octamer are studied. The oxidation potentials and the formation and stability of the different oxidized species are influenced by the oligothienoacene chain length. The effect of the steric hindrance caused by the substituents on the -dimerization of the radical cations is also investigated by comparing a trimethylsilyl (TMS) substituted pentathienoacene with a TIPS substituted one.