Characterization of SiO2-TiO2 Hybrid Corrosion Protective Coatings on Mild Steel

Abstract

Organic-inorganic SiO2-TiO2 sol-gel coatings were prepared and applied on a mild steel substrate using dip coating technique and subsequently heat treated at 200 and 300 °C to improve the corrosion resistance. The coating sols were synthesized using Glycidoxytrimethoxysilane and titanium tetraisopropoxide as precursor materials. The corrosion resistances of the both coated and uncoated samples were evaluated by the Tafel polarization and electrochemical impedance spectroscopy in NaCl solution. The microstructure of coated specimens was characterized by scanning electron microscopy. Fourier transformed infrared and energy dispersive spectroscopy analyses were used to identify the presence of various functional groups in the coating solutions. A comparison of the corrosion resistance of the coated and uncoated mild steel was presented. i corr values of coated specimens heat treated at 200 °C were between 6.9 and 9.2 times smaller than those of uncoated specimen. In the case of coated specimens heat treated at 300 °C, i corr values were 4.4 and 5 times smaller than those of uncoated specimen. The coating film was noted to be smooth and between 7.2- and 7.5-µm thick. The measured electrochemical parameters indicated that the corrosion resistance was improved by the coating film. The elasticity of the coating can be improved by the presence of organic groups in the coating which reduces stress and crack formations during sintering. Ultimately, crack-free and elastic coating was obtained by heat treating of organic-inorganic coating at as low as 200 °C.