Chemical and spectrophotometric studies of naphthol dye as an inhibitor for aluminium alloy corrosion in binary alkaline medium

The inhibition of a substituted naphthol compound, 4-(4-nitrophenylazo)-1-naphthol (44NIN), on the corrosion of aluminium (Al) in a basic medium was studied by classical chemical (gravimetric) and spectrophotometric (UV-Vis and FTIR) methods at 303-333 K. 44NIN demonstrated an excellent inhibiting property to Al corrosion in the aerated binary alkaline solution as shown from the results. The inhibition efficiency was found to increase with the azo dye concentration but not with temperature. Thermodynamic and adsorption evaluation for this inhibition process were accessed and thoroughly discussed. The UV-visible absorption spectra of the solution containing this dye after the immersion of Al specimen indicate the possible formation of a 44NIN-Fe type complex. The FTIR was carried out of the dye and protective film formed on the surface of the metal in the electrolyte containing the dye after a 72 h immersion period. These results show a correlation between the inhibitive effect and molecular structural information of 44NIN in this typical heterogeneous alkaline system.