Acid-functionalized oil fly ash (f-OFA-COOH) was reacted with zinc oxide (ZnO) for the in-situ growth of an inhibitor (ZnO) on functionalized oil fly ash, forming f-OFA-ZnO. f-OFA-ZnO was used to synthesize waterborne polyurethane (WBPU) dispersions with defined f-OFA-ZnO contents. The dispersions were used as a protective coating on mild steel. The protective properties varied with f-OFA-ZnO contents. The maximum adhesive strength, highest water contact angle and minimum water swelling were recorded using 2.00 wt% f-OFA-ZnO. All coatings were exposed near a seaside to evaluate their atmospheric corrosion protective properties. Most of the coatings corroded slightly. A significant improvement in corrosion protection was observed for only the coatings with higher f-OFA-ZnO contents, which were prepared by the in-situ polymerization method
Corrosion occurring in atmospheric conditions is called atmospheric corrosion. The factors that can tune this type of corrosion are atmospheric criteria such as rain, dust, UV light, humidity and marine aerosols [1, 2].
Protective coatings are usually applied on metal surfaces to protect the metal and their structure from atmospheric corrosion. The trickiest part is choosing a proper coating because the protective properties of coatings also deteriorate with environmental variations. Thus, a protective coating that is very good in one area might not work in another area. A protective coating should be selected by considering local environmental factors [3, 4].
Many protective coatings are available commercially. Among them, polyurethane (PU) is a protective coating used very widely to protect metal surfaces from atmospheric corrosion. Unfortunately, its protection ability deteriorates under harsh atmospheric conditions, such as high-intensity UV light, high temperatures and marine aerosols. To avoid this deterioration in protective properties, different methods have been adopted in the last decade. Different additives and inhibitors are mixed with PU coatings to improve their protective properties. Many different fillers are also mixed with PU to improve its protective properties. However, mixing additives, inhibitors and fillers in coating solutions can destroy the shelf-life of coating dispersions. The adhesive and mechanical properties of the final coating also deteriorate by the excess loading of additives, inhibitors and fillers. Currently, academic and industry people are looking for a single filler/inhibitor/pigment to fulfill all protection purposes [5-7].
