Influence of Multiple Coating and Heat Treatment Cycles on the Performance of Nano-TiO2 Coating in Protection of 316L Stainless Steel against Corrosion under UV Illumination and Dark Conditions

In this study nanosized TiO2coatings on the 316L stainless steel substrate were prepared by means of dip-coating technique in which thickness of the coating layer increased byrepeating the coating cycles in two different routes: (I) dipping and drying,respectively, were repeated one, three and five times and finally the dried coated sample was heat treated (single); (II) multiple heat treatment performed after each dipping and drying cycle, respectively.The structural, morphological and optical characterizations of coatings as well as thickness of coatings were systematically studied.The photocatalytic activity of the various TiO2 coatings was investigated based on the degradation of an aqueous solution of Methyl orange.Moreover, thecorrosion protective properties of coatings were evaluated in both dark and UV illumination conditions based on the obtained polarization curves. The results indicated 1.75 times improvement in photocatalytic reaction rate constant, a two orders of magnitude decrease in corrosion current density in dark condition and about 140 mV electrode potential reduction under UV illumination with optimum coating preparation procedure, repeating the cycle from dipping to heat treatment three times, than the sample prepared with one time coating and heat treatment since this procedure provided not only high thickness and defect-free coating but also transparent one.