Multilayered ZnO/TiO2 nanostructures as efficient corrosion protection for stainless steel 304

Abstract

ZnO/TiO2 coatings are deposited onto 304 stainless steel substrates by using sol-gel dip-coating technique followed by subsequent annealing. X-ray diffraction analysis reveals nanocrystalline ZnO and TiO2 phases for all multilayered films except 1ZnO/1TiO2 with amorphous nature. Optical microscopy images show the presence of some streaks, holes, scratches and micro-traces, meanwhile the obtained coatings present different colours, from grey to yellowish. Scanning electron microscopy observations indicate that the deposited films are smooth, uniform, with low level of cracks. Surface topography analysed by atomic force microscopy confirms the smoothness of the coatings; the roughness is very low 0.764–5.166 nm. UV–vis spectroscopy analysis indicates that the energy bandgap varies according the nature and order of the deposited layers; 3.32 eV for 1TiO2/1ZnO up to 3.68 eV for 2TiO2/2ZnO. Corrosion tests were carried out, especially potentiostatic (EIS) and potentiodynamic (Tafel plots). The corrosion protection performance for stainless steel 304 (304SS) has been evaluated in 3% wt NaCl solution. The obtained results reveal that the 1TiO2/1ZnO multilayered thin film exhibits a remarkable improvement in anticorrosion performance; reaching a very high efficiency protection of 98%. This has been attributed to the double protective layer (TiO2-Tetragonal/ZnO-Hexagonal) preventing the diffusion of corrosive ions through the surface.