Preparation of corrosion protective coatings on galvanized iron from aqueous inorganic–organic hybrid sols by sol–gel method

New inorganic–organic hybrid precursors for corrosion protective coatings on galvanized iron were prepared by adding 3-glycidyloxypropyltrimethoxysilane (GPS) to an aqueous nanosized boehmite solution. Transparent boehmite (AlOOH) sols were prepared at 100 °C by peptizing aluminum hydroxide cake, which was obtained from the reaction between aqueous aluminum chloride and aqueous ammonium hydroxide solution (pH 8). Three different types of precursor sols, such as pure boehmite, hydrolyzed GPS, and boehmite–GPS hybrid sols were prepared and they were deposited on ultrasonically cleaned galvanized iron plates by using dip coating technique at room temperature. All the coatings were cured at 100–180 °C for 0.5–5 h in air, and their anticorrosion behavior was studied by analyzing the potentiodynamic polarization curves at room temperature. It was observed that the coatings cured at 150 °C for 3 h with GPS to boehmite molar ratio=0.7 exhibited the maximum corrosion resistance property, which attributed to the formation of a dense microstructure by cross-linking of functionalized nanoparticles.