The Formation Behavior of TiO_2 Thermal Sprayed Coatings Using Nano-Powders and Their Photo-Catalytic Properties(Materials, Metallurgy & Weldability, INTERNATIONAL SYMPOSIUM OF JWRI 30TH ANNIVERSARY)
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TiO_2 coatings were prepared by High Velocity Oxy-Fuel (HVOF) spraying using agglomerated sub-micron and nano-TiO_2 powders (200nm, 30nm, 7nm). The effects of various spraying conditions on microstructure, anatase phase ratio, coating thickness have been investigated and then photo-catalytic properties were evaluated. It was found that anatase phase ratio decreased drastically with increasing fuel gas pressure in the case of 7nm agglomerated powders (P_7 powders), while a higher anatase ratio was obtained in the case of agglomerated 200nm and 30nm powders (P_<200> and P_<30> powders). Anatase ratios greater than 60% could be achieved when agglomerated 30nm powders were sprayed. This means that 30nm agglomerated powders were showing lower susceptibility to heat effect and provided higher photo-catalytic activity. When agglomerated 7nm agglomerated powders were sprayed, individual particles were easily subjected to heat affect and then became 30nm by rapid grain growth. On the other hand, since large increases of anatase particle (grain) size were not detected when agglomerated 30nm powders were sprayed, it was assumed that an approximately 30nm particle was the limit size and optimum size for HVOF spraying. These coatings showed photo-catalytic decomposition of gaseous acetaldehyde (CH_3CHO). As a result of photo-catalytic experiments, TiO_2 coating formed by HVOF spraying using 30nm powder showed a higher decomposition rate because of higher anatase ratio.
- Transactions of JWRI
Transactions of JWRI 32(1), 175-178, 2003-07