Ceramics from the titanium-oxygen system were prepared by sintering TiO_2 and Ti_2O_3 powders at 1400 deg C in air or in Ar/H_2 (7 percent). The surface compositions of the TiO_2, the non-stoichiometric TiO_(2-x) and the Ti_2O_3 ceramics, studied with X-ray photoelectron spectroscopy, are discussed in terms of their chemical composition, with particular emphasis on the valence state of the titanium ions. The correlation between the valence state of the titanium ions at the surface and the water-contact angle was examined. The presence of Ti~(3+), which can be introduced at the titanium-oxygen ceramic surface by sintering the ceramic in lower oxygen partial pressure, is related to a significant decrease in the water-contact angle. TiO_2 ceramics with just Ti~(4+) at the interface had a water-contact angle of 67 deg; however, the non-stoichiometric TiO_(2-x) and Ti_2O_3/Ti_3O_5 with Ti~(3+) at the interface had lower water-contact angles, i.e., 26 deg and 18 deg, respectively. The wettability of ceramics in the Ti-O system can be improved by introducing Ti~(3+) at the ceramic interface.
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