Biomedical Engineering Reference
In-Depth Information
Figure 9.43
Nanotube length (coating thickness) vs. electrolyte
temperature for the anodization of Ti for 2 h in 1M H
2
SO
4
+ 0.1M NaF solution at a constant potential of 20 V, and
pH 5.0 [13].
Chemical dissolution and ield-assisted dissolution were
considered to play key roles in the formation of nanotubes [74].
Mor
et al
. [58] suggest that unanodized materials part could exist
between the pores and ield-assisted oxidation/dissolution of
these interpore regions, resulting in the formation of voids. The
growth of voids in equilibrium with pores has been considered
to render nanotubular structure. Slight altering electrochemical
condition could result in pores or tubes formation. Both structures
can be produced in comparable electrolytes. The luoride ions are
necessary in the formation of nanoporous structure [123], but
when anodization is conducted at higher potentials (>200 V), the
porous ilm is possible to do in non-luoride containing solutions
[121]. Because the dielectric breakdown occurs, the pores are not
uniform with cracks in the oxide ilm. Formation of nanoporous
layer in luoride solutions required a much lower voltage (<40 V)
while the pores are well separated and self-ordered.
The anodic oxidization is a relatively simple technique
for preparing highly oriented uniform nanotube arrays. The
anodization can be conducted at either high or low potentials of
typically [5, 10, 58, 80, 92]. At low potential, chemical dissolution
of the titanium oxide play a key role in the formation of nanotube
arrays. The formation is determined by the balance between the
electrochemical oxidization and the chemical dissolution [10].
When the electrochemical oxidization proceeds faster than the
