Aluminum basic benzoate-based coatings: evaluation of anticorrosive properties by electrochemical impedance spectroscopy and accelerated tests

Abstract

Insoluble metallic benzoates can be prepared from the corresponding soluble salts. Soluble benzoates can be used as inhibitors in neutral solutions while insoluble ones can be used as anticorrosive pigment for paints. This paper describes the experimental procedure to prepare aluminum basic benzoate (AlC14H11O5) to be used in anticorrosive paints. The anticorrosive properties of aluminum basic benzoate were assessed by electrochemical techniques (corrosion potential and linear polarization measurements). The nature of the compounds forming the protective layer was determined using spectroscopic techniques (scanning electron microscopy /energy-dispersive x-ray microanalysis [SEM-EDAX], ultraviolet [UV]-visible diffuse reflectance, Fourier transform infrared [FTIR], and Mössbauer). In a second stage, the anticorrosive properties of the pigment were evaluated by incorporating it in alkyd and epoxy anticorrosive paints, which, in turn, were evaluated by accelerated (salt spray and humidity tests) and electrochemical measurements (electrochemical impedance spectroscopy). The morphology and the nature of the protective layer grown under the paint film in the salt spray chamber was assessed using SEM and UV-visible diffuse reflectance spectroscopy. Experimental results showed that basic aluminum benzoate was adequate to formulate solvent and water-borne epoxy anticorrosive paints with improved anticorrosive performance when it is used in combination with zinc oxide (ZnO). Zinc oxide counteracted the intrinsic acidity of basic aluminum benzoate. Solvent alkyd paints could also be prepared but with lower performance.