Corrosion protection of 1008 carbon steel by hybrid coatings

Abstract

Potentiodynamic polarisation curves have been used to evaluate the corrosion performance of 1008 carbon steel coated with hybrid (inorganic-organic) and mixed oxide coating systems deposited by dip coating. Several coatings have been prepared by the sol-gel method, using metallic alkoxides, such as tetraethylorthosilicate, aluminium isopropoxide, and zirconium propoxide, and polymers like allyl methacrylate (AMA) and polymethylmethacrylate (PMMA), together with zirconium dioxide (ZrO2) and silicon and aluminium oxides (SiO2-Al2O3). The aqueous test solutions included hydrochloric acid (HCl), sodium chloride (NaCl), and sulphuric acid (H2SO4) at various concentrations (0.1, 0.5, and 1M). Scanning electron microscopy was used to examine the coatings following testing. The results have shown that SiO2-Al2O3 based coatings are not beneficial for corrosion protection in HCl, but are of value in the other aqueous media. In 1.0M HCl, the best protection was offered by a hybrid SiO2-ZrO2-poly(methylmethacrylate-allyl methacrylate) (P(MMA-AMA)) coating. In NaCl, the best results, were generally obtained with SiO2-Al2O3 and SiO2-ZrO2-P(MMA-AMA) coatings. Similarly, in H2SO4, the best results were generally displayed by the SiO2-Al2O3 and SiO2-ZrO2-P (MMA-AMA) coatings The corrosion behaviour of the coatings is discussed in terms of the integrity and stability of the film.