Effect of Thickness and Multilayer Characteristic on the Photocatalytic Properties of the Multilayer Nano-Structured Titania Coatings on 304L Stainless Steel

This research is intended to cover the creation of multilayer nanostructured titania coating on 304L stainless steel by sol-gel dip-coating method to study the effect of thickness and multilayer characteristic on the photocatalytic properties of this coating. A stable polimeric sol based on Titanium Tetraisopropoxide with diethanolamine as additive was used in the coating process and by repeated immersion process، coating samples with 1 to 5 layers were prepared using two methods، one stage heat treatment and multistage heat treatment. To investigate the properties of samples، following analysis methods are used; TG، DTA، XRD، SEM، AFM، surface roughness test and photocatalytic tests under UV and VIS irradiation. Analysis results of XRD، SEM and AFM showed nanometric scale of TiO2 particles in the coating samples. No evidence of discontinuity has been detected during cross section area examination of multi-layer coatings using SEM. The analysis results of DTA، TG and XRD showed the formation of crystalline anatase phase from the amorphous phase at temperatures around 350°C، then anatase to rutile phase transformation begins at 500°C، and finally completes at 700°C. The optimal temperature for heat treatment was determined as 450°C which is also confirmed by the results of photocatalytic tests. The effect of thickness and layer numerity on the photocatalystic propeties of cotings is one of the discovered results in this research. From the point of photocatalytic properties، the optimum thickness of titania coating was determined around 198nm، which belonged to 3-layers coating with three stage heat treatment. The average surface roughness (Ra) in multilayer coating samples with multistage heat treatment has been decreased from 0. 107 µm in one layer sample to 0. 0147 µm in five layer sample، when layer numbers increased