study of the behaviour of AI, Cu and AI-Cu couple in sodium carbonate solutions.

ABSTRACT

In case of copper, oxide film thickening occurred and the open circuit steady state potential shifted slightly towards more negative values; while in case of Al, either alone or coupled with copper, oxide film thickening occurred at lower concentrations <10-3 but at higher than 10-3 M; dissolution of the oxide took place and the potential was shifted to more negative values. Potentiostatic polarization confirmed the above results. The galvanic potential measurements of Al-Cu couple in different aerated or oxygenated carbonate solutions indicated that at concentrations <10-3 M, the potential shifted to less negative values; while at higher concentrations, a more negative shift was recorded and Al anode was severely attacked. Addition of 3.5% NaCl shifted the potential to more negative values at lower carbonate concentrations. Galvanic current Ig measurements indicated a decrease in the current strength values at the moment of contact followed by a steady state value. The steady state galvanic current Ist against logarithm of carbonate concentration showed a more or less regular increase of Ist with increase of electrolyte concentration