Investigation of the Corrosion Resistance of Carbon Steel Surface with Oligomeric Silsesquioxane Composite Fluozirconic Acid Conversion Film

For improving the corrosion resistance of carbon steel surfaces， a phosphorus free and chromium free fluorozirconic acid composite oligomeric silsesquioxane conversion film was prepared using fluorozirconic acid composite amino/hydroxyl polyhedral oligomeric silsesquioxane(NH2/OH-POSS).The corrosion resistance， surface morphology and composition of the composite film were characterized by saltwater immersion， electrochemical testing， scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).Results showed that the optimal process for the fluoro-zirconate solution combined with the NH2/OH-POSS aqueous solution was 1.2 g/L fluorozirconic acid， 4.5 g/L oligomeric silsesquioxane， pH of 4， the temperature of 30 ℃， the passivation time of 2 min.The saltwater immersion test and electrochemical test indicated that the corrosion resistance of the composite conversion film was significantly improved compared to the pure fluorozirconic acid conversion film.SEM results revealed that the addition of oligomeric silsesquioxane filled the cracks and pores in the fluoro-zirconate film，making the film denser.XPS results confirmed that both oligomeric silsesquioxane and fluoro-zirconate participated in the formation of the conversion film.