Biomedical Engineering Reference
In-Depth Information
Ban
et al
. [3] investigated the etching behavior of titanium
in concentrated sulfuric acid at 60°C for 0.25, 0.5, 1, 3, and 8 h
(Fig. 9.4). The etching reveals grain boundaries and the crystal
grains are well visible. On the surface are etched pores with
diameter less than 1 μm. The depth of the etched grain boundaries
and pores increases with etching time [3].
Figure 9.5
Surface roughness
R
a
and
R
z
, and weight loss of Ti after etching
in 48% H
2
SO
4
in the range from RT to 90
°C
for 0.25-8 h [3].
The surface roughness and weight loss of the Ti increase with
the acid temperature and etching time (Fig. 9.5) [3]. A signiicant
difference occurs between the acid temperature and the etching
time for roughness and the weight loss. The etching of Ti in
concentrated H
2
SO
4
involves the following reactions:
TiO
2
+ 2H
2
SO
4
→
Ti(SO
4
)
2
+ 2H
2
O
(9.1)
Ti + 2H
2
SO
4
→
Ti(SO
4
)
2
+ 2H
2
(9.2)
Ti + H
2
→
TiH
2
(9.3)
Surface roughness is strongly correlated with weight loss.
At the beginning of the etching, the formation rate exceeds the
rate of TiH
2
dissolution, and the relative amount of TiH
2
on the Ti
surface increases. The dissolution rate of TiH
2
also increases with
time, because the surface area increases with the increase in surface
roughness due to the etching.