A Comparative Study on the Electrochemical Behaviour of Aluminium and 8090 Al- Li-Cu-Mg Alloy in Acid Rain Solution
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.