Photocatalytic Decomposition of Ammonia by Thermal Sprayed TiO_2 Coatings

摘要

TiO_2 coatings were prepared by plasma and HVOF spray using agglomerated sub-micron TiO_2 powder. Effects of various spray conditions on microstructure, phase ratio, coating thickness have been investigated and then photo-catalytic 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 percent) 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 NH_3. As a result of photo-catalytic experiments, TiO_2 coating formed by HVOF spraying showed higher decomposition rate because coating by HVOF showed high anatase ratio. And, moreover, the TiO_2 coating by plasma spray technique also exhibited photo-catalytic decomposition of gaseous NH_3 although anatase ratio was lower in comparison with HVOF in present study.