The phase of a TiO 2 layer formed on commercially pure Ti by two-step thermal oxidation using N 2 CO gas was investigated. The oxidation process comprised two steps: treatment in an N 2 (0.1, 1 and 5)%CO atmosphere and treatment in air. A Ti(C,N,O) phase was formed after the first-step treatment conducted at 8731123 K. In the second step, the oxidation of this phase at 573773 K resulted in the formation of an anatase phase, while its oxidation at 873 K resulted in the formation of a single rutile phase. An increase in the CO partial pressure in the first step lowered the temperature for anatase phase formation. Further, in the second step, a single-phase anatase layer was formed at temperatures of 623 and 673 K.

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Two-step thermal oxidation was proposed for Ti and Ti alloys as a surface-treatment process for preparing an anatase-containing TiO 2 layer. This process consisted of treatment in a CO-containing atmosphere (first step) and subsequent treatment in air (second step). In this chapter, first, the current status of TiO 2 coating onto Ti and Ti alloys for biomedical applications is reviewed; then our recent work on the phase and microstructure of TiO 2 layers prepared on commercially pure (CP) Ti, Ti-25mass%Mo alloy, and Ti-25mass%Nb alloy by two-step thermal oxidation is described. The anatase fraction in the TiO 2 layer was controlled through process parameters such as the second-step temperature. Finally, photocatalytic activity of TiO 2 layers formed on the Ti and Ti alloys is evaluated, including: results of water contact angle, decomposition of methylene blue, and antibacterial effects.