Characterization Of Photocatalyst Optical Properties Under Vacuum Conditions
- Paper number
IAC-07-C2.I.13
- Author
Mr. Fumitaka Urayama, Space Engineering Development Co., Ltd., Japan
- Coauthor
Prof. Mutsuhisa Furukawa, Japan
- Coauthor
Dr. Kiyoshi Ozawa, National Institute for Materials Science, Japan
- Coauthor
Dr. Masahiro Tosa, National Institute for Materials Science, Japan
- Coauthor
Dr. Hideo Kimura, National Institute for Materials Science, Japan
- Year
2007
- Abstract
Organic molecular contaminants, induced by spacecraft material outgassing and thruster firing, accumulate onto the critical surfaces such as the thermal control systems and the optics, and can degrade their thermo-optical performances. While photocatalytic decontamination is studied actively under atmospheric conditions in world-wide, the photocatalysts have new potential to apply to decontamination in space environment. We focus attention on photocatalyst of semiconductor crystal which has a potential to decontaminate the organics under ultraviolet irradiation condition in space. Absorption of a photon with energy greater than the band gap energy results in the formation of conduction band electron and valence band hole. It is commonly accepted that the hole is quickly converted to the hydroxyl radical upon oxidation of surface water, and chemical reaction between the radical and the organics results in oxidative decomposition of the organics. In our previous studies, Japan Aerosil’s P25 TiO2 particles and/or synthesized Ti(OH)x particles were used as photocatalysts, on which H2O adsorbs even at room temperature under the vacuum condition. Squalene, oleamid and methyl-phenyl siloxane were used as representative molecular contaminants. Mass loss of the organics with the P25 and/or Ti(OH)x is approximately two times lager than the organics alone. We found out a capability of TiO2 and/or Ti(OH)x to decompose organics under vacuum conditions. In the next stage, we have studied the change in photocatalyst optical properties with the organics, using photocatalyst-coated substrates. The experiment apparatus consists of ultraviolet light source, vacuum chamber with two view ports, Pirani gauge and ionization gauge, and UV/VIS spectrometer. The apparatus can make in-site measure the transmittance of the substrate installed in the vacuum chamber. We introduce the results of the experiments and discuss the factors of the change in the optical properties.
- Abstract document