Nano-TiO2 Phosphate Conversion Coatings – A Chemical Approach

Abstract

The present study aims at deposition of zinc phosphate coatings on low carbon steel with incorporated nano- TiO 2 particles by chemical phosphating method. The coated low carbon steel samples were assessed in corrosion studies using electrochemical impedance spectroscopy and potentiodynamic polarization techniques (Tafel) in 3.5% NaCl solution. Morphology and chemical composition of the coatings were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy in order to observe growth of coating. Significant variations in the coating weight, porosity and corrosion resistance were observed with the addition of nano- TiO 2 in the phosphating bath. Corrosion rate of nano-TiO 2 chemical phosphate coated samples was found to be 3.5 milli inches per year which was 3 times less than the normal phosphate-coated sample (8 mpy). Electrochemical impedance spectroscopy studies reveal reduction of porosity of nano-TiO 2 phosphate coated samples. It was found that nano-TiO 2 particles in the phosphating solution yielded uniform phosphate coatings of higher coating weight, fewer defects and enhanced corrosion resistance than the normal zinc phosphate coatings (developed using normal phosphating bath).