ABSTRACT
Figure 5.7 SEM micrographs of the Ti foils anodized at 20 V in 1 M H3PO4 + 1 M NaOH + 0.3%wt HF for (a) 20 min and (b) 4 h (top view). Idem from cross section for (c) 20min and (d) 4 h.
(JCPDS file 21-1272), respectively. On the other hand, the Ti layer deposed on Si substrate was identified as hexagonally close-packed α-Ti (JCPDS file no.: 44-1294) and the ntTiO2 nanotubes obtained at room temperature are X-ray amorphous. On heating we observe again the partial crystallization of titania to anatase (Fig. 5.9c). Peaks of Ti are still present after growing the ntTiO2 not only onto Ti foils but also onto Si because a layer of Ti (1.25 μm in thickness) remains after anodization (see SEM image in reference [34]). In the particular case of the silicon substrate, 35% of the initial Ti layer is converted into ntTiO2. This remaining Ti layer is not electroactive versus lithium, as it is discussed later.
