In alkali solutions, corrosion of aluminium occurs at a high rate with the passivation of the metal accompanied by hydrogen evolution. Several organic compounds have been tried as corrosion inhibitors. The inhibition efficiency was brought down by the high-negative potential of the reaction, which would simply repel any organic compound in the electrical double layer (Antropov, 1961). Nevertheless, quite a large number of organic compounds inhibit corrosion in dilute solutions but eventually fail at higher concentrations. Carbonic acids (Horiguchi et al., 1966), aliphatic and aromatic amines (Sarangapani et al., 1984), diketones (Horiguchi et al., 1966), phenolic compounds (Subramanyan et al., 1971) alkaloids (Subramanyan and Ramakrishnaiah, 1971) alizarin derivatives were tried as inhibitors. The present investigation aims at the development of polyaniline as corrosion inhibitor. In the present study, addition of ZnO in solution shifted the corrosion potential to noble direction by forming a film. The conductivity of the film has been enhanced by incorporating polyaniline.

The corrosion of aluminium has been inhibited by the combined action of polyaniline and ZnO. The formation of an oxide film encapsulated with polyaniline prevented the dissolution of aluminium. Inhibitors of aluminium corrosion in aqueous medium have been reviewed. In aqueous solution, the surface film formed on aluminium is of duplex in nature consisting of an inner amorphous Al₂O₃and outer crystalline aluminium oxides. These films inhibit corrosion in the initial stages but weaken this film due to the incorporation of OH– ions into this structure and accelerate corrosion. In presence of excess OH– ions, aluminium dissolves to form aluminate. Additions of organic compounds inhibit to a lesser degree. Owing to the high negative electrode potentials, they desorb and accelerate corrosion. Most of the organic inhibitors inhibit hydrogen evolution reaction to some extent.

The purpose of this work (A. Elango et al., 2010) is to show how to develop inhibition 57S aluminium in 2M NaOH solution. The results of the work clearly reveal that the 0.2 M ZnO with 700 ppm polyaniline in N-methyl-2-pyrrolidone solution is found to offer inhibition up to 71.2 per cent. The paper deals with the development of newer inhibitor based on polyaniline. Gravimetric and galvanostatic methods were employed to evaluate inhibition efficiency.

References:

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7. A. Elango, V. M. Periasamy, M. Paramasivam, and E. Rakesh, (2010), “Novel polymeric inhibitor for corrosion of 57S aluminium in 2M NaOH solutions,” Anti-Corrosion Methods and Materials, vol. 57, no. 1, pp. 3–5.