TiO_2 nanotubes with different morphology were prepared by treatment of TiO_2 nanocrystals in mild hydrothermal conditions in alkaline solution. TiO_2 nanotubes were characterized by TEM, XRD, FT- Raman and BET specific surface area techniques. THe effects of particle size and crystalline phase of TiO_2 nanoparticles on the morphology of the resulting nanotubes were investigated. TEM and BJH pore size distributions show that the ultrafine rutile-typed nanoparticles in size of 7.2 nm can form much longer nanotubes than derived from rutile in larger size or in the anatase phase. The formation mechanism of long TiO_2 nanotubes was interpreted in the light of the relative stability of crystalline phase and the dependence of reactivity on the particle size under mild hydrothermal condition in the alkaline solution.

Key words: TITANIUM DIOXIDE, NANOPHASE MATERIALS, TEM, XRD, GRAIN