Nano-AI203 doped coatings for corrosion protection of Cu-based artefacts

摘要

In this study some organic coatings, commonly used in conservation-restoration of bronze artefacts were doped with Al_2O_3 nano-pigment to deposit aesthetic coatings with improved corrosion protection properties. The protective effectiveness of the nano-doped coatings, deposited on Cu-based reference alloys, was assessed by means of electrochemical impedance spectroscopy (EIS) and polarization resistance measurements as a function of the immersion time in chlorides containing solution at room temperature. Different formulations of Paraloid (B72 and B67) and Incralac, diluted in toluene and acetone in different percentage (10 - 20 w/w%) and doped with 2% of Al_2O_3 nano-pigments were tested. These formulations had practically similar viscosity ensuring similar thickness of the dry films. All the coatings cover uniformly the metallic surface and no pigment agglomeration is observed. Paraloid B72 coating with the addition of 2% Al_2O_3 nano-pigment, exhibited fewer defects in comparison to the films obtained with higher Al_2O_3 nano-pigment percentages, as confirmed by the morphological characterization carried out by scanning electron microscopy. The nano-pigment enhances the coating protective ability and probably prevents the metal ions diffusion at the solid/liquid interface; however too high particle loadings induce agglomeration, which degrades the coating performance through inclusion of voids that can act as preferential sites for crack initiation and coating failure.