Development and evaluation of an eco-friendly hybrid epoxy-silicon coating for the corrosion protection of aluminium alloys

The present research work is focused on the formulation, synthesis and evaluation of three novel eco-friendly hybrid epoxy-silicon (EP-S) coatings. For comparative purposes, two commercial epoxy (EP) coatings were also evaluated. The protective properties of the coatings were evaluated by means of Electrochemical Impedance Spectroscopy (EIS), also supported by physico-chemical characterization of the coated surfaces by Fourier Transformed Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), as well as Contact Angle (CA) and Energy Surface measurements. The very high impedance (Z) values confirmed the excellent protective properties and the suitability of the novel EP-S coatings to protect 5005 aluminium substrates exposed to a simulated harsh marine environment (10% (w/w) NaCl solution), when compared with commercial EP coatings providing an adequate corrosion protection performance. Surface characterization tests to the hybrid coatings corroborated their excellent barrier properties. The comparison of the IR spectra before and after immersion test in the referred NaCl solution demonstrated the absence of water inside the EP-S coatings. Additionally, the very high water contact angle (>90°) and low surface energy values, confirmed the hydrophobic nature as well as the low wettability of the hybrid coatings. It was concluded that the addition of silane containing an amine functional group allowed obtaining a denser and more effective protective coating.