Portugaliae
Electrochimica Acta

This work is devoted to examine the effectiveness of pyrazoles 4-(4,5-dihydro-1H-pyrazol-5-yl)-N,N-dimethylaniline (D) on corrosion of mild steel in a 1 M HCl solution, using weight loss measurement at concentration effects. The inhibitor (D) was synthesized in our laboratory. The formation of this pyrazole was carried out with hydrazine and α-unsaturated aldehydes, and the structure was checked by spectroscopic means, such as FT-IR, 1H NMR and 13C NMR. Polarization curves and electrochemical impedance spectroscopy (EIS) methods were used to assess both the corrosion rate and inhibition efficiency. Potentiodynamic polarization showed that D behaved as a mixed-type inhibitor. The Nyquist plots showed that, while D concentrations increased, charge-transfer resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. Adsorption of the inhibitor molecules corresponds to Langmuir adsorption isotherm. Quantum chemical calculations showed that the inhibitor was prone to be protonated in the acid, and the results were in full agreement with experimental observations.

The degradation of the AB1 dye by electro-generated species using a BDD electrode was performed. The results were explained by the generation of OH* radical, S2O82− in the presence of sulfate, and active halide species in the presence of halide salt. The discoloration rate increases in this order: sulfate, KCl, KBr. In the presence of KCl, the discoloration is affected by the current density, initial pH, temperature, and concentration of the supporting electrolyte; however, the concentration of the dye and the ionic strength showed a negligible effect. The intermediates produced during the discoloration are a function of the pH of the solution. In the presence of sulfate, the discoloration rate is very slow, and the mechanism of discoloration is different from that in the presence of KCl. The thermodynamic parameters of the discoloration are calculated.

This work has investigated the effect of addition of the Be alkaline earth metal on the dissolution behaviour of the Al-Zn alloy anode. Corrosion experiments were mounted to determine the optimal effect of an alkaline earth metal on the efficiencies of the aluminium alloy anodes. The corroded and unexposed sample surfaces were subject to microstructural characterization by using scanning electron microscopy and X-ray diffraction techniques. Al-Zn alloy doped with 1-5% by weight of beryllium was prepared to determine the effect on the anode efficiency in chloride environment. The different microstructure of the evolved Al-Zn alloy was correlated with the anode efficiencies. The obtained results showed that the anode efficiency of the Al-Zn alloy increased with the beryllium incorporation concentration. Al-Zn-Be-3% exhibits the better performance in terms of anode efficiency. The microstructure of the Al-Zn-Be alloy revealed increased distribution of beryllium globules and a breakdown of passive alumina film network on the anode surfaces, thus improving the anode efficiency.

The electrochemical behavior of catechol in the presence of sulfanilic acid has been examined in aqueous solution with numerous pH values, different electrodes and different concentration of sulfanilic acid, using cyclic voltammetry, controlled potential coulometry and differential pulse voltammetry. The reaction of o-benzoquinone with sulfanilic acid in the second scan of potential was observed. It is assumed that the reaction occurred between the sulfonate group of sulfanilic acid and quinone, rather than between the amino group of sulfanilic acid and quinone. The products derived from the reaction are associated with electrons transfer at more negative potentials than those from catechols. The significance of catechol’s pH in presence of sulfanilic acid was studied by varying pH from 2 to 9. The concentration influence of sulfanilic acid with the fixed concentration of catechol (2 mM) was determined from 2 mM to 12 mM. The reaction was toughly affected by the pH, as well as by the concentration of sulfanilic acid. The reaction was mostly promising in 2 mM of sulfanilic acid and 2 mM of catechol at pH 7.

The effect of the concentration and nature of novel 3-hydroxy-3-(4-chlorophenyl-1-(4-sulphonato (sodium salt)) phenyl triazene (HCST) on corrosion and dezinfication of 70/30 brass in 0.5 M HNO3 solution has been investigated by weight loss method. Inhibition efficiency of this corrosion inhibitor was also evaluated at different temperatures ranging from 303 K-333 K. It was observed that HCST showed 88.13% inhibition efficiency at 303 K up to 0.005 M concentration of inhibitor. Weight loss method has been used to analyze the corrosion behavior of the brass in the absence and presence of different concentrations of inhibitor. The corrosion inhibition efficiency increases with increasing concentration of inhibitor and decreases with rise in temperatures. Activation energy (Ea), enthalpy (∆H), entropy (∆S) and Gibbs free energy (∆G) for corrosion process have also been calculated. The adsorption behavior of HCST on brass surface has been found to obey Langmuir adsorption isotherm. Results reveal that hydroxytriazenes can be potential corrosion inhibitors.