An environmental-friendly tannic acid/Zn conversion film with a good corrosion protection for iron

Because traditional chromating and phosphating processes are harmful to the environment and human health, an eco-friendly tannic acid (TA)-based conversion film technology is established by adopting a new self-assembly strategy of TA/metal complexes on iron surfaces in aqueous solutions. In this study, TA and TA/Zn films were conveniently fabricated by anchoring a certain amount of TA molecules on the iron surface through the coordination interaction between phenolic hydroxyls and metal ions. In contrast, the introduction of Zn ions in the film-forming process cannot only complex with more TA molecules to form a thicker conversion film but also accelerate the film-forming process and transform into ZnO, which can further inhibit iron corrosion. This combination leads to the excellent corrosion protection of TA/Zn film-modified iron (the corrosion protection efficiency is up to 92.39%). Moreover, impact tests show that the TA/Zn film can enhance the adhesion between the iron substrate and outer coating.