No abstract

The inhibition of copper corrosion by Helichrysum italicum extract (HI) in simulated acid rain was investigated using electrochemical techniques. Results indicate an increase in corrosion inhibition efficiency with the HI extract concentration. The inhibitive process was assumed to occur via adsorption of the extract on the metal surface. The thermodynamic data indicated physical adsorption and followed the Freundlich isotherm. The effect of temperature on the copper corrosion was studied. The value of the activation energy confirmed physisorption of extract molecules on the copper surface. The concentration of Cu ions released into solution, measured by atomic absorption spectrometry, was in accordance with the electrochemical results.

The aqueous extract of the Helichrysum italicum leaves (HI) is tested as a corrosion inhibitor of an iron in a simulated acid rain using potentiodynamic polarisation, cyclic voltammetry and electrochemical impedance spectroscopy. Results of all electrochemical methods indicate an increase of a corrosion inhibition efficiency of the iron with the HI extract concentration. Maximum inhibition efficiency (~ 50 %) is obtained at 2.0 g L–1 HI extract. The inhibitive action is assumed to occur via an adsorption of the HI extract on the iron surface. Results indicate that the adsorption process is spontaneous and follows the Freundlich adsorption isotherm. According to the calculated ΔG value (~ 15 kJ mol–1), the corrosion inhibition of the iron occurs predominantly via a physisorption of the HI extract. The concentration of iron ions released into a solution, measured by atomic absorption spectrometry, is in accordance with the electrochemical results.

The growth mechanism and properties of the oxide films on aluminium and 8090 Al-Li-Cu-Mg alloy were studied in simulated acid rain (pH 4.5) by electrochemical techniques, cyclic voltammetry and electrochemical impedance spectroscopy. The potentiodynamic formation of anodic oxide film on aluminium and 8090 Al-Li-Cu-Mg alloy surfaces were described in terms of high field model. This is justified by the obtained values of kinetic parameters: the electric field strength (~10 6 V cm -1 ), ionic conductivity through the film (~10 -12 S cm -1 and 10 -13 S cm -1 ) and half jump distance (~0.150 nm). The impedance data shows that protective passive oxide film on aluminium and Al-Li-Cu-Mg alloy can be formed spontaneously at the open circuit potential in the studied solution with a high resistance (119 k cm 2 for Al and 144 k cm 2 for Al-Li-Cu-Mg alloy). Both electrochemical techniques revealed that the oxide film on Al-Li-Cu-Mg alloy has better protective properties than pure aluminium. The concentration of the metallic ions released into solution from aluminium and Al-LiCu-Mg alloy and measured by atomic absorption spectroscopy was in accordance with the results obtained from the electrochemical techniques.

The effect of the aqueous extract of Achillea millefolium L. (AM) on the electrochemical behaviour of iron in a simulated acid rain solution (pH 4.5) was studied by electrochemical techniques cyclic voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy. Experiments were carried out over a wide range of AM concentrations. The results of all techniques showed that AM extract contributes to iron passivation. The films formed in the presence of AM extract were thinner and more resistive then the films formed in pure simulated acid rain solution. The AM extract adsorbed on the iron according to the Freundlich isotherm. The thermodynamic data indicated physical adsorption of the AM extracts on the iron surface. The concentration of the metallic ions released into solution, measured by atomic absorption spectroscopy, was in accordance with the results obtained from the electrochemical techniques.