Surface-decorated silica with Schiff base as an anticorrosive coating for aluminium alloy 2024-T3

Abstract

Schiff base orthosilicate 7 was synthesised and its inhibitory properties against corrosion when deposited on the 2024-T3 aluminium alloy in 0.05 mol·L−1 NaCl were investigated by electrochemical impedance spectroscopy, potentiodynamic polarisation and scanning electron microscopy technique. Polarisation curves indicated that the orthosilicate 7 studied acts by decreasing the anodic and cathodic activity on the alloy surface, and presents effective barrier properties as an anticorrosive conversion layer, retarding the corrosion and pitting potentials of alloy. The electroactivity of Schiff base orthosilicate 7 was attributed to the presence of nitrogen and oxygen atoms and the flexible spacer group which showed better adsorption properties on metallic surfaces by forming complexes between 7 and metals. Specific potentials can produce different Schiff base orthosilicate 7 complexes on the metal surface according to the reduction wave at around −1.1 V on platinum, and −0.27 V on AA2024-T3 (vs. the platinum pseudoreference microelectrode). The proposed protection mechanism is based on the adsorption of the silicate portion on the matrix phase of the alloy, by metaloxosilane bonds (AlOSi), and by complexed structures in the flexible group chain of the Schiff base portion on intermetallics enriched by copper (N----Cu+2 and O----Cu+2).