Biomedical Engineering Reference
In-Depth Information
chemical dissolution, the barrier layer grows, which in turn reduces
the electrochemical oxidization process to the rate determined by
the chemical dissolution [11]. The chemical dissolution rate
determines the nanotube length [10]. When the chemical dissolution
does not occur, the further anodization is obstructed by the oxide
layer and higher potential up to hundreds volts are needed to break
the barrier layer [11].
Raja
et al
. [74] investigated a nanotube formation during
anodization of Ti foil at constant 20 V in the following electrolytes:
0.5M H
3
PO
4
+ 0.138M HF, 0.5M H
3
PO
4
+ 0.138M NaF, 0.5M
H
3
PO
4
+ 0.138M NaCl, 0.5M H
3
PO
4
+ 0.138M NaBr. They show
evolution of the nanoporous structure during etching in 0.5M
H
3
PO
4
+ 0.14M HF at constant potential of 20 V (Fig. 9.44). After
10 s etching are observed, a microcracks acts as a nucleation
points for nanopores during anodization for longer period.
Figure 9.44
Stages of nanotubular ilm evolution during anodization
at 20 V in 0.5M H
3
PO
4
+ 0.14M HF solution: from micro-
cracks through pores to a thick oxide with self-organized
nanotubes [74].
