Portugaliae
Electrochimica Acta

The aim of this study was to produce thin films of ternary cobalt-nickel-iron (Co-Ni-Fe) alloy by electrochemical deposition method at different electrodeposition potentials in a sulfate solution (0.15 M CoSO4 + 0.2 M NiSO4 + 0.005 M FeSO4). The Co-Ni-Fe alloy thin films were electrodeposited on indium-doped tin oxide (ITO) coated on a conducting glass substrate. Voltammetric studies indicated the potential range between -1.10 to -1.30 V (SCE) for successful deposition of Co, Ni and Fe. The energy dispersive X-ray (EDX) analysis indicated that the films exhibited anomalous behavior with Ni content significantly increased, whereas the Co and Fe content decreased as the electrodeposition potentials reached more negative values. The scanning electron microscopy (SEM) study showed that the electrodeposited films were uniform for all applied potential values and larger particles were formed when higher electrodeposition potentials were applied. Investigation by X-ray diffraction (XRD) revealed that the dominant phase in the deposited film was amorphous Co-Ni-Fe. Hysteresis curves of the ternary alloy film obtained from vibrating sample magnetometer results prove that the alloy is ferromagnetic. The coercivity mechanism of the Co-Ni-Fe films has obeyed Neel’s relation which is thickness dependence.

The environmental friendly inhibitor system L-cysteine-Zn2+ has been investigated by weight loss method. A synergistic effect exists between L-cysteine and Zn2+ system. The formulation consisting of 250 ppm of L-cysteine and 50 ppm of Zn2+ offers an excellent inhibition efficiency of 99%. Polarization study reveals that this formulation functions as anodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra study leads to the conclusion that the Fe2+- L-cysteine complex formed on the anodic sites of the metal surface controlled the anodic reaction, and Zn(OH)2 formed on the cathodic sites of the metal surface controlled the cathodic reaction. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from weight loss study and surface analysis technique. Synergism parameters have been calculated. They are found to be greater than 1, suggesting that a synergistic effect exists between L-cysteine and Zn2+.

Annatto extract (dye) was investigated as a cheap and ecologically friendly alternative corrosion inhibitor. The corrosion process was monitored with mild steel coupons in 1.0 M hydrochloric acid at temperatures between 30 oC to 90 oC by weight loss and spectroscopic techniques. The dye effectively inhibited the corrosion of mild steel in the acid at the studied temperatures. Inhibition efficiency obtained was found to vary with temperature and concentration of the dye. Adsorption models were used to predict the nature of the dye-steel surface interaction. Thermodynamic models provided evidence of spontaneous physical and chemical adsorption mechanism with the evolution of heat. Kinetic studies revealed a deepening effect on the activation potential in the presence of the dye. The effect of solvent and synergistic intensifiers on the effectiveness of the dye was also assessed. Heavy metal ion composition in the formulation was determined and was within the limit of environmental and health safety.

N-pyridinium salt derivatives (1), (2), (3), (4) and (5) were prepared and their inhibition effect as corrosion inhibitors for mild steel was investigated in 1 M H2SO4 solution at 30 oC for 24 hs. The corrosion inhibiting action was studied using weight loss measurements. The results have revealed that the corrosion rate decreases, inhibition efficiencies increase and surface coverage degree increases with a higher inhibitor’s concentration. Inhibition efficiencies for prepared N-pyridinium salt derivatives have the highest inhibiting efficiency even for a low concentration. The values of Goads are showing physisorption effect for all prepared compounds. Molecular modeling systems were achieved for the suggested inhibitors (1), (2), (3), (4) and (5). Theoretical calculations could be used as a useful tool to obtain information for explaining the mechanism and nature of interaction between the metal surface and the organic molecule as a corrosion inhibitor.

The peculiarities of the metallographic structure of electrodeposited nanocomposite polymeric modified Zn and Zn-Co (1 wt.%) alloy coatings are described and discussed. These coatings are obtained from usual electrochemical baths for Zn and Zn-Co alloys, but with the addition of stabilized polymeric micelles (SPM). The latter are of core-shell type, and are based on polypropylene oxide (hydrophobic core) and polyethylene oxide (hydrophilic shell). These coatings and their polymeric modified nano-composites are investigated with X-ray (XRD) method, which reveals changes in the metallographic structure as a result of the presence or absence of organic additives (wetting agent and brightener) and SPMs. The possible reasons for the changes observed are commented. In addition, cyclic voltammetry method (CVA) is applied in order to clarify the influence of the applied additives and of SPM on the cathodic (deposition) and anodic (dissolution) processes.