Porous oxide films obtained by anodic oxidation attract a great deal of attention due to their unique microstructure. The structure of as-synthesized films can be characterized as an array of cylindrical channels in amorphous metal oxide with perpendicular orientation to metallic substrate and narrow size distribution. This feature makes anodic titania films promising elements of gas sensors, selective and catalytic membranes. However, these applications require high thermal and mechanical stability of anodic oxide membranes, and crystallinity of the pore walls.

In the present work we studied crystallization and evolution of the microstructure under thermal treatment. Anodic titania was obtained by anodic oxidation of metallic titania in 0.25% NH₄F ethylene glycol solution at 60V. According to thermal analysis mass loss (up to 11,5%) accompanied by two exothermal effects at 220^oC and 330^oC which is observed during heating to 375^oС can be ascribed to decomposition and removal of electrolyte from the pores. According to XRD data crystallization of amorphous titania into anatase begins at 300^oC and finishes at 420^oC. Crystallinity degree runs up to 85% and crystalline size runs up to 40 nm during heating to 375^oC . According to SEM data porous structure are stable up to 600^oC.

Thus the minimal temperature for crystallization of anodic TiO₂ is 420^oC and operating temperatures of membranes and sensors based on anodic TiO₂ can be varied form room temperature to 600^oC.

This work was supported by RFBR (grants 06-03-89507, 06-08-01443) and FASI (grant 02.523.12.3015)

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