Sodium titanate nanotube/titanium metal composites were synthesized by hydrothermal treatment of titanium metalswith various morphologies such as plate, wire, mesh, microsphere, and microtube at 160
![](/images/entities/deg.gif)
C in aqueous NaOH solutionand by the subsequent fixation treatment by calcination at 300
![](/images/entities/deg.gif)
C. The surface of the composite was covered withsodium titanate nanotubes with a diameter of approximately 7 nm, and the core part of the composite was titaniummetal phase. The raw titanium metal acts as a template or a morphology-directing agent of micrometer size or moreto arrange the nanotubes as well as a titanium source for the formation of nanotubes. The concentration of titaniumspecies increases in the reaction solution as the dissolution of titanium metal is accelerated by the reaction betweentitanium and OH
-. Furthermore, with an increase in concentration of titanium species in the reaction solution, thetitanium species are reprecipitated as sodium titanate nanotubes onto the titanium metal. Titanium metal with a largesurface area and volume can form sodium titanate nanotubes on the surface of the titanium metal, though titaniummetal with a small volume and surface area tends to dissolve with the hydrothermal treatment. Even in the synthesisusing titanium metal with a small volume and surface area, sodium titanate nanotubes are formed and cover the surfaceof the titanium metal by adding another titanium metal as a source of titanium species in the reaction solution.