effect of coating drying conditions on bronze corrosion protection

Abstract

Waterborne coatings present a green alternative to solvent-borne coatings as only a small amount of organic solvent is released into the environment during drying. However, for waterborne coatings, the drying process is much more challenging due to the slow evaporation of water. In this work, the influence of drying temperature on the protective properties of a waterborne acrylic coating was studied. Its performance in corrosion protection of bronze substrates, representing the bronzes used for the sculptures placed outdoors, was examined. Corrosion properties were evaluated by linear polarization measurements and electrochemical impedance spectroscopy during three-week exposure to artificial acid rain solution. It was found that drying at ambient temperature resulted in modest corrosion protection, while drying at 55 °C ensured greater initial corrosion resistance, which gradually degraded during exposure to acid rain solution accompanied by the coating blistering. Drying of one-layer coating at 40 °C resulted in the formation of clearly visible corrosion products. If the coating was applied in three layers, the drying process was more efficient, leading to slightly higher polarization resistance values without visible corrosion at the bronze surface. Furthermore, the studied waterborne acrylic coating provided good corrosion protection of patinated bronze surfaces. Additionally, it was found that for efficient corrosion protection, it is preferable that the coating contains a corrosion inhibitor in order to avoid substrate corrosion during coating drying. When applied properly, studied coating does not alter the state of surfaces, both bare and patinated, which is important for its application in bronze cultural heritage protection.