Corrosion behaviour of aluminium in ethyleneglycol-water electrolytes containing phosphonic acid

The inhibitor effect of ethylenediaminetetraphosphonic acid (EDTPO) on the corrosion behaviour of Al in ethyleneglycol-water mixtures has been investigated through electrochemical and atomic force microscopy measurements. It has been evidenced that the adsorption of EDTPO on the surface of Al is favoured in these media as compared to an aqueous solution with the same nominal 8.4 pH value. This effect is more pronounced in mixtures containing over 20% of ethyleneglycol in water (v/v), and 0.1 mol L−1 sodium tetraborate as supporting electrolyte. The presence of EDTPO promotes the repairing of the passive film defects on the Al surface through a sealing process, which increases the stability of the oxide film layer. Moreover, the film shows greater uniformity, lesser porosity and remains stable for longer immersion periods as compared to those grown in the absence of EDTPO.