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Characterization of polypyrrole films deposited on aluminum surfaces from oxalic acid aqueous solution

100%

Liu S. , Oliveira M. A. S.

tom Vol. 27, No. 1

265--278

Electrochemical synthesis of polypyrrole films (PPy) on aluminum surfaces from oxalic acid aqueous solutions was performed using the cyclic voltammetry and galvanostatic technique. SEM micrographs of aluminum surfaces coated with PPy films showed that the galvanostatically deposited films were more homogeneous than those deposited by cyclic voltammetry. The presence of bands at 1170 and 1630 cm-1 in the FTIR spectra of the PPy films indicate that the films are overoxidised. The corrosion protection of aluminum surfaces coated with polypyrrole films was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy in a chloride medium. A poor corrosion protection performance of the PPy films was observed and it was associated with the overoxidation process, resulting in defects and pores along the polymeric chain that allows penetration of corrosive species.

Influence of aliphatic organic acids on the properties of PPy films electrodeposited on aluminum surfaces

100%

Liu A. S. , Oliveira M. A. S.

Advances in Materials Science

2007

tom Vol. 7, nr 2(12)

223-235

Polypyrrole (PPy) films were galvanostatically deposited on 99.9 wt.% aluminum e1ectrodes from aqueous solutions containing each carboxylic acid: tartaric, oxalic or citric. The thickness of the PPy films was measured by Perfilometry. It was observed that PPy films electrodeposited from oxalic acid medium were thicker than those electrodeposited from the electrolytes containing the other twa organic acids. This observation was a consequence of the nature of the oxide layer produced during the electrodeposition of PPy. More compact oxide layers difficult the electron-transfer reactions and consequently the pyrrole oxidation. The morphology and roughness of the aluminum surfaces coated with the polymeric films were analyzed by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), respectively. It was observed that the films deposited from tartaric acid medium presented higher homogeneity and smaller roughness than those formed in oxalic and citric acid media. Furthennore, the corrosion protection of aluminum surfaces by PPy films was also investigated by potentiodynamic polarization experiments. These experiments demonstrated that the aliphatic acids also influence the corrosion protection afforded by the PPy films on aluminum surfaces.