Biomedical Engineering Reference
In-Depth Information
After long etching time, the top nanoporous layer is dissolved. The
higher HF electrolyte concentration results in faster dissolution.
Figure 9.10
Porous TiO
x
formed after etching at 10 V for 30 min in
1 M H
3
PO
4
electrolyte containing: 0.5% HF (a), 2% HF (b),
10% HF (c); (1 × 1, 10 × 10 and 40 × 40 μm, respective scans
size) [28].
On Fig. 9.11 shows the surface of the pure microcrystalline Ti
after etching in 1M H
3
PO
4
+ 10% HF electrolyte at 10 V vs. OCP
for 5 min [31]. Etching results in surface roughening and pits
formation. The diameter and the depth of the pits are about 4-5 and
1-2 μm, respectively. The pits' dimensions differ for different process
conditions, (like H
3
PO
4
and HF concentration, etching time and
applied voltage or current density) [28] and hence pits' diameter
can vary from nano- to micrometer range. Etching at low potential of
1 V vs. OCP for 60 min reveals an initial etching stage (Fig. 9.12a).
The surface etched in 1M H
3
PO
4
+ 0.35% HF has crack-like
morphology (Fig. 9.12a) and large remnants of the lat surface are
visible [28]. The increase of the HF concentration up to 2% (Fig.
9.12b) results in uniformly etched pores. This different behavior
is related with increasing HF concentration, which results in faster
etching.
