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.

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 growth kinetics and electrochemical properties of the oxide film formed on iron were studied in 0.01 and 0.1 mol L −1 NaF solutions with different pH values (4.5, 5.5 and 6.5) by cyclic voltammetry and electrochemical impedance spectroscopy. The growth of the oxide film on iron in potentiodynamic conditions, characterized by the occurrence of "current plateau" recorded on the cyclic voltammograms, showed that the growth of the oxide film takes place by low-field migration mechanism. The ionic conductivity of the oxide during its growth (~ 10 −12 S cm −1 ) and the electric field strength through the oxide (~ 10 6 V cm -1 ) were calculated. Thickness of oxide film is dependent upon the solution pH and fluoride concentration; thinner and more compact film forms in solution with lower fluoride concentrations and higher pH values. Impedance measurements were carried out on the potentiostatically formed oxide films after electrode stabilization for 30 minutes at the open circuit potential (EOCP). The charge transfer resistance and the electrode capacitance were determined. The resistance value, as well as EOCP value, decreases with increasing concentration of F − and lowering the pH. Corrosion rate values were computed from charge transfer resistance and it was found that corrosion rate increased with increased F − concentration and decreased pH, being highest in 0.1 mol L −1 NaF, pH=4.5 (60.69 g cm -2 h -1 ) and lowest in 0.01 mol L −1 pH=6.5 (0.25 g cm -2 h -1 ).