Biomedical Engineering Reference
In-Depth Information
Figure 9.54
Pore diameter and interpore distance of nanotubular
titanium oxides ilms after anodization in 1M H
2
SO
4
+
0.15 wt% HF at RT as a function of voltage [6].
Hydroluoric acid concentration plays a major role in pore
formation and dissolution. Steady-state nanotubular formation is
possible, when the concentration of HF is in the range of 0.15-0.4
wt% [6]. After 24 h of anodization, the thickness of nanotubular
titanium oxide ilms reaches 400-500 nm. The cell voltage plays a
key role in titania structure. Using an electrolyte 1M H
2
SO
4
+ 0.15
wt.% HF, it is possible to obtain a rutile structure at low voltages
and a mixture of anatase and rutile at higher voltages [6]. Annealing
the titanium oxide ilms result in the formation of anatase or rutile
crystal structure (Fig. 9.55, 9.56) as well. XRD patterns of the titanium
oxide, obtained after anodizing in 1M H
2
SO
4
+ 0.15 wt% HF at
15 V, and annealing at temperature increasing from 200 to
600°C, are shown on Fig. 9.55 [6]. Both rutile and anatase crystal
forms have tetragonal structure. The anatase phase prevails by
annealing at 300 and 400°C, while at 600°C, the rutile structure
appears. Annealing time also affects the crystallization process
(Fig. 9.56). The anatase phase formation proceeds after 180 min
of annealing, while for longer time annealing, the rutile phase
appears [6].
