Cold Spraying of TiO 2 Photocatalyst Coating With Nitrogen Process Gas
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JTTEE5 19:1218–1223 DOI: 10.1007/s11666-010-9520-1 1059-9630/$19.00 Ó ASM International
Cold Spraying of TiO2 Photocatalyst Coating With Nitrogen Process Gas Motohiro Yamada, Hiroaki Isago, Hiromi Nakano, and Masahiro Fukumoto (Submitted February 12, 2010; in revised form May 24, 2010) Titanium dioxide (TiO2) is a promising material for photocatalyst coatings. However, it is difficult to fabricate a TiO2 coating with anatase phase by conventional thermal spray processes due to a thermal transformation to rutile phase. In this paper, anatase TiO2 coatings were fabricated by the cold spray process. To understand the influence of process gas conditions on the fabrication of the coatings, the gas nature (helium or nitrogen) and the gas temperature are investigated. It was possible to fabricate TiO2 coatings with an anatase phase in all spraying conditions. The process gas used is not an important factor to fabricate TiO2 coatings. The thickness of the coatings increased with the process gas temperature increasing. It indicates that the deposition efficiency of the sprayed particles can be enhanced by controlling the spray conditions. The photocatalytic activity of the coatings is similar or better than the feedstock powder due to the formation of a large reaction area. Concludingly, cold spraying is an ideal process for the fabrication of a TiO2 photocatalyst coating.
Keywords
ceramic, cold spray, deposition, nitrogen oxide, process gas
1. Introduction Titanium dioxide (TiO2) is an attractive material with respect to its photocatalytic property. To use a TiO2 photocatalyst coating to remove air pollutants such as nitrogen oxide (NOX) and acetaldehyde, formation of a large area coating is required. Conventionally, thermal spray processes have been widely used for the fabrication of a thick and large area coating. Therefore, there are a number of studies about fabrication of a TiO2 photocatalyst coating by several thermal spray processes (Ref 1-5). Fabrication of a TiO2 coating is not difficult by thermal spray processes, though it has been difficult to obtain a coating which has a high photocatalytic property. The photocatalytic performance of TiO2 is significantly affected by its crystal structure. TiO2 in anatase phase provides a higher photocatalytic activity than that in rutile phase (Ref 6, 7). The anatase phase irreversibly transforms into rutile phase over 900 °C which is lower than the melting temperature of TiO2 (1908 °C). Since with processes having a temperature higher than the melting
This article is an invited paper selected from presentations at the 4th Asian Thermal Spray Conference (ATSC 2009) and has been expanded from the original presentation. ATSC 2009 was held at Nanyang Hotel, XiÕan Jiaotong University, XiÕan, China, October 22-24, 2009, and was chaired by Chang-Jiu Li. Motohiro Yamada, Hiroaki Isago, Hiromi Nakano, and Masahiro Fukumoto, Toyohashi University of Technology, Toyohashi, Aichi, Japan. Contact e-mail: [email protected].
1218—Volume 19(6) December 2010
temperature of TiO2, ther
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