Portugaliae
Electrochimica Acta

Three different films modified with silver species were considered to enhance the corrosion resistance of AZ91D Mg alloy and to impart its surface with antibacterial activity. First, coatings were electrodeposited under potentiostatic conditions in electrolyte solutions containing Na2MoO4 and/or Ce(NO3)3 as main compounds, and H2O2, ascorbic acid or citric acid as additives. Incorporation of silver species was done by immersion of the samples in AgNO3 solutions. The obtained modified films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion protection properties of the films were examined in a simulated physiological solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The antibacterial effect of the coatings was evaluated using Escherichia coli bacteria. Cerium and molybdenum-based coating modified with silver provides superior antibacterial and anticorrosive properties compared to the other films studied.

The present work is focused on the influence of the metal salts on the photocatalytic efficiency of TiO2 for the elimination of E 131 VF food colorant. Two series of TiO2 photocatalysts loaded with Fe(II) and Cu(II) were prepared by using the wet impregnation method. The samples were characterized by XRD, IR, Raman and scanning electron microscopy. The degradation of the food colorant was followed by the measurement of the absorbance. The kinetics of degradation fitted well to the zero pseudo order with Cu-TiO2, but it followed the 1st order with Fe-TiO2. In general, the photoactivity of TiO2 was reduced by the presence of the transition metal ions, even at low molar ratio %. The recalcination of the doped samples at higher temperatures reduced more the degradation activity. Several reasons were suggested to explain the dramatic decrease in the activity of the prepared samples.

Molecular modelling approach has been used for the prediction of anticorrosion properties of 1, 2, 4-triazole derivatives on steel in acidic medium by the quantum chemical calculation and molecular dynamics (MD) simulation methods. Quantum chemical parameters such as the highest occupied molecular orbital (E-HOMO), the energy of the lowest unoccupied molecular orbital (E-LUMO), energy band gap (ΔE), dipole moment, global electronic chemical potential (μ), chemical softness (σ), chemical hardness (η) and electrophilicity (𝜔) have been calculated and discussed. The reactive sites of the inhibitor molecules were found to be on the nitrogen-atom of the Triazolic ring and on the π-electron centers. Furthermore, molecular dynamics simulation was applied to search for the best inhibitor adsorption configuration over Fe (110) surface. The best adsorption energy was found to be -430.27 kcal/mol (inhibitor 3). The adsorptions occurred via chemisorption.

The inhibitory activity of ethanol extract of Nerium oleander leaf (NOLE) on carbon steel corrosion in 0.5 M and 1.0 M of hydrochloric acid solutions was studied by weight loss method and electrochemical techniques. The inhibition efficiency (w) increased with an increase in the concentration of NOLE and in temperature. Polarisation curves indicated that NOLE acts as a mixed type of inhibitor. The changes in charge transfer resistance (Rt) with increasing inhibitor (i.e. NOLE) concentration assured the adsorption of the inhibitor onto the metal surface. The results of w, p (inhibition efficiency obtained from polarisation study) and R (inhibition efficiency obtained from impedance analysis) are in par with each other. Surface morphology study uncovered the coating of the inhibitor molecule on the metal surface. The phenomenon of physical adsorption has been established based on the inhibition efficiency of the inhibitor with change in temperature.

In cooling water systems, seawater can be used. L 80 can be used as a pipeline for carrying sea water. However, this alloy will undergo corrosion. Corrosion can be prevented by the addition of inhibitors such as sodium potassium tartrate (SPT), trisodium citrate (TSC) and zinc sulphate. Corrosion resistance of L 80 alloy in sea water, in the absence and presence of the above inhibitors, has been evaluated by polarization study and AC impedance spectra. It was observed that SPT and TSC show better inhibition efficiency in the presence of Zn 2+. Further, it was found that the SPT-Zn system is better than the TSC-Zn system.