Biomedical Engineering Reference
In-Depth Information
is observed due to the formation of a dense oxide layer by the
dissolution of Ti:
Ti + 2H
2
O
→
TiO
2
+ 4H
+
+ 4e
−
(9.8)
The inal thickness of this oxide layer is related to the applied
potential. In stage 2, in the presence of F
−
, chemical dissolution of
TiO
2
is possible:
TiO
2
+ 4H
+
+ 6F
−
→
Ti F
6
2−
+ 2H
2
O (9.9)
Stage 2 is characterized by the formation of nanopores across
the surface of the TiO
2
layer. The formation of nanopores results in
an increase in current density, local dissolution of TiO
2
, and
increasing the electric ield intensity at the bottom of the pore. The
increased current density drives the formation of new oxide at the
metal/oxide interface while also increasing the rate of chemical
dissolution at the oxide electrolyte interface [13].
Figure 9.39
Schematic showing the mechanism for TiO
2
nanotube
formation [13].
