Titanium Dioxide Coatings Sprayed by a Water-Stabilized Plasma Gun (WSP) with Argon and Nitrogen as the Powder Feeding G
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. Ctibor, Z. Pala, J. Sedla´cˇek, V. Sˇtengl, I. Pı´sˇ, T. Zahoranova´, and V. Nehasil (Submitted September 9, 2011; in revised form January 12, 2012) Titanium dioxide coatings were sprayed by a water-stabilized plasma gun to form robust self-supporting bodies with a photocatalytically active surface. Agglomerated nanometric powder was used as a feedstock. In one case argon was used as a powder-feeding as well as coating-cooling gas whereas in the other case nitrogen was used. Stainless steel was used as a substrate and the coatings were released after the cooling. Over one millimeter thick self-supporting bodies were studied by XRD, HR-TEM, XPS, Raman spectroscopy, UV-VIS spectrophotometry and photocatalytic tests. Selected tests were done at the surface as well as at the bottom side representing the contact surface with the substrate during the spray process. Porosity was studied by image analysis on polished cross sections where also microhardness was measured. The dominant phase present in the sprayed samples was rutile, whereas anatase was only a minor component. The hydrogen content in the nitrogen-assisted coating was higher, but the character of the optical absorption edge remained the same for both samples. Photoelectron spectroscopy revealed differences in the character of the O1s peak between both samples. The photocatalytic activity was tested by decomposition of acetone at UV illumination, whereas also the end products—CO and CO2—were monitored. The nitrogen-assisted coating was revealed as a more efficient photocatalyst. Certain aspects of a thermal post-treatment on the coatings are discussed as well. Color and electrical conductivity are markedly changed at annealing at 760 °C, whereas only very small changes of the as-sprayed coating character correspond to annealing at 500 °C.
Keywords
bandgap, photocatalysis, resistivity, spectroscopy, TiO2
1. Introduction Titanium dioxide (TiO2) has many applications, namely in photo-catalytic, dielectric and optical-coating components. This article is an invited paper selected from presentations at the 2011 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Thermal Spray 2011: Proceedings of the International Thermal Spray Conference, Hamburg, Germany, September 27-29, 2011, Basil R. Marple, Arvind Agarwal, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Andre´ McDonald, Ed., ASM International, Materials Park, OH, 2011. P. Ctibor and Z. Pala, Institute of Plasma Physics, ASCR, Za Slovankou 3, 182 00 Praha 8, Czech Republic; J. Sedla´cˇek, Department of Electrotechnology, Faculty of Electrical Engineering, Czech Technical University, Technicka´ 2, Praha 6, Czech Republic; V. Sˇtengl, Institute of Inorganic Chemistry, ASCR, Husinec-Rez 250 68, Czech Republic; and I. Pı´sˇ, T. Zahoranova´, and V. Nehasil, Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Praha 8, Czech Republic. Contact e-mail:
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