Polyacrylic acid as a corrosion inhibitor for aluminium in weakly alkaline solutions. Part I: Weight loss, polarization, impedance EFM and EDX studies

This part is devoted to study the influence of three selected polyacrylic acids (PAAs) with different molecular weights (PAA1 = 1800, PAA2 = 11,000 and PAA3 = 14,000 g mol−1) on the corrosion inhibition of Al in weakly alkaline solutions (pH 8 and 10) at 30 °C. Measurements were conducted under different experimental conditions using chemical (weight loss) and electrochemical (potentiodynamic polarization and impedance) techniques, complemented with ex situ energy dispersive X-ray (EDX) examinations of the electrode surface. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented here. The results demonstrated that these polymers inhibit the alkaline corrosion of Al. The inhibition effect of these polymers is due to their adsorption on Al surface. The isoelectric point (IEP) of aluminium oxide (pH 9) seems to be an important factor controlling corrosion inhibition and adsorption of the three polymers. The three polymers inhibit the corrosion reaction of aluminium excellently at pH 8, but less effectively at pH 10. Polarization measurements showed that the three polymers act as mixed-type inhibitors. The inhibition efficiencies of these polymers increase with increasing concentration, molecular weight and immersion time. Results obtained from the chemical and electrochemical measurements are in good agreements.