Two-step thermal oxidation of commercially pure Ti was investigated with a focus on the formation of anatase. A first-step treatment was conducted in Ar-(0.1-20)%CO atmosphere at a temperature of 773-1173 K for a holding time of 0 or 86.4 ks, and a subsequent second-step treatment was conducted in air at 473-873 K for 0-86.4 ks. Titanium oxides and titanium oxycarbide were obtained in the first step, with relative amounts depending on heating temperature, holding time, and CO partial pressure. An anatase-rich layer on Ti was obtained after second-step treatment in air at 573-773 K in cases where single-phase titanium oxycarbide formed in the first step. Thus, the formation of single-phase titanium oxycarbide in the first step and temperature control in the second step were required for the formation of an anatase-rich layer. The bonding strength of an anatase-rich layer with a thickness of 0.5 μm was calculated to be around 90 MPa. This study reveals the conditions under which an anatase-rich layer with excellent adherence to Ti can be prepared by thermal oxidation.
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