Photocatalytic Decomposition of Ammonia by Thermal Sprayed TiO₂ Coatings

TiO₂ coatings were prepared by plasma and HVOF spray using agglomerated sub-micron TiO₂ powder. Effects of various spray conditions on microstructure, phase ratio, coating thickness have been investigated and then photocatalytic properties was evaluated. It was found that anatase phase ratio decreased gradually with increasing arc current in the plasma spray process, while higher anatase ratio (approximately 50%) was obtained in the HVOF process. The coating thickness increased with increasing arc current and displayed approximately 50mm thickness in the case of 800A although anatase ratio was lower. Thus, the anatase phase ratio and coating thickness exhibited strong dependency on thermal spray method and spray conditions (arc current and fuel gas pressure). The sprayed coatings using sub-micron powder feed showed photo-catalytic decomposition of gaseous NH₃. As a result of photo-catalytic experiments, TiO₂ coating formed by HVOF spraying showed higher decomposition rate because coating by HVOF showed high anatase ratio. And, moreover, the TiO₂ coating by plasma spray technique also exhibited photocatalytic decomposition of gaseous NH₃ although anatase ratio was lower in comparison with HVOF in present study.