Construction of a high-performance anti-corrosion film based on the green tannic acid molecules and zinc cations on steel: Electrochemical/Surface investigations

Construction of organic-inorganic films on the metal substrates for achieving a desirable degree of metal protection in front of chloride-induced corrosion has become the recent researches topic. In this regard, the environmentally friendly compounds have drawn more attention. One of the natural and biodegradable compounds with promising corrosion inhibition potency is tannic acid (TA). In this work, the synergistic inhibition of the TA molecules and zinc cations (Zn (II)) in saline solution was evaluated. EIS technique and Tafel polarization method were applied for studying the efficiency as well as the mechanism of the corrosion inhibitors. To characterize the structure and composition of the organic-inorganic based complexes formed on the steel plates, FE-SEM, FT-IR, and GIXRD were employed. To obtain the hydrophobicity level of the metal surface, contact angle (CA) measurements, utilizing water as the probe liquid, were conducted. The EIS outcomes evidenced that mixing the TA molecules and Zn (II) ions is a practical protocol for effective steel corrosion resistance enhancement. Polarization achievements demonstrated that an effective corrosion inhibition of steel by the mixed-mode mechanism occurred due to the formation of the TA-Zn based film. According to the electrochemical techniques outcomes, the 250 ppm TA + 750 ppm Zn (II) sample evidenced about 80% efficiency after 168 h. FE-SEM images and GIXRD analysis outcomes verified that a protective film based on the TA-Zn complexes precipitated on the steel sample. EDS and FT-IR analysis results confirmed that a complex between the TA molecules and Zn (II) species was formed. The presence of the TA-Zn (II) complex on the steel sample resulted in a less hydrophilic surface and more protective film.