Fabrication and Properties of TiO_2 Photo-Catalytic Coatings by Thermal Spraying with TiO_2-Al Agglomerated Powder(Materials, Metallurgy & Weldability)

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In the present study, anatase TiO_2 photo-catalytic coatings were fabricated by plasma and HVOF spraying. In order to prevent the transformation from anatase to rutile phase, lower heat input conditions were adopted. For the improvement of bondability between coatings and substrate, anatase TiO_2-Al agglomerated powder was used for the experiment. The microstructures of the coatings were characterized with SEM and XRD analysis, and the photo-catalytic characteristics of coatings were evaluated by the decomposition rate of acetaldehyde gas. Due to the addition of aluminum, thick coatings were formed even at lower heat input conditions in both plasma and HVOF spraying. The results of XRD analysis for the plasma sprayed coatings, however, indicated the disappearance of anatase phase and deoxidization of TiO_2 to Ti_3O_5 or magneli phase. On the other hand, high anatase/rutile ratio and high photo-catalytic efficiency were achieved for the coatings formed by HVOF spraying. The temperature measurements of flying particles were also carried out using DPV-2000. As a result, significant increases in temperature of TiO_2-Al particles were observed compared with the case of using pure TiO_2 particle. These results suggest that a chemical reaction between TiO_2 and Al occurs during thermal spraying.
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