TiO2 coatings were prepared by High Velocity Oxy-Fuel (HVOF) spraying using agglomerated nano-TiO2 powders (200nm, 30nm and 7nm). The effects of spraying conditions on microstructure, anatase phase ratio, coating thickness have been investigated and then photo-catalytic properties were also evaluated. Although the anatase phase ratio decreased drastically with increasing fuel gas pressure in the case of agglomerated 7nm-powders (P7 powders), while higher anatase ratio could be obtained in the case of agglomerated 200nm and 30nm powders (P200 and P30 powders). Especially, anatase ratio more than 70% and thickness greater than 30µm could be achieved when 30nm-agglomerated powders (P30 powders) were sprayed. This means that 30nm agglomerated powders have lower susceptibility to heat. It was assumed that approximately 30nm particle was the limit size and optimum size for HVOF spraying. These coatings showed photo-catalytic degradation of gaseous acetaldehyde (CH3CHO). As a result of experiments, TiO2 coating formed by HVOF spraying using 30nm powder showed higher decomposition rate because of higher anatase ratio.

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