Biomedical Engineering Reference
In-Depth Information
z
et al
. [7] investigated the corrosion resistance of pure
nano-Ti grade 2 after hydrostatic extrusion. They found that the grain
size of the titanium substrate did not inluence the thickness of oxide
formed on the titanium. Passive oxide layers formed on the surface of
coarse-grained Ti (CG Ti) and nano-grained Ti (NG Ti) had thickness
of about 6 nm in both cases, and the same chemical composition. NG
Ti shows slightly lower corrosion resistance in 0.9% NaCl solution
with respect to CG Ti (Table 5.5).
Table 5.5
Speciication of corrosion potentials values (
E
corr
) and
corrosion currents density (
I
corr
) for CG and NC Ti [7]
Ni-type
E
corr
(mV)
I
corr
(A cm
-2
)
CG Ti
-152
18
NG Ti
-158
41
5.2
Corrosion of the Ti-Based Porous Materials
Porous metallic materials are attractive for biomedical applications,
for example in dental or orthopedic hard tissue implants. The
main problem of these materials is the relatively poor corrosion
resistance, due to the rough surface. The corrosion resistance of
porous titanium and its alloys in simulated body luid is signiicantly
lower than that of bulk counterparts [1, 8, 42], but the surface is
attractive for osseointegration.
Jakubowicz investigated corrosion resistance of the oxidized
porous Ti in Ringer's electrolyte, corresponding to human bio-
environments (NaCl, 9g/L; KCl, 0.42 g/L; CaCl
2
, 0.48 g/L; NaHCO
3
,
0.2 g/L) [14]. Figure 5.22 presents potentiodynamic curves for
pure Ti (a) and TiO
x
(b), which characterize corrosion behavior of
the materials with native and anodic oxides, respectively.
Polarization curves of both, pure Ti with native oxide (a) and
Ti foil with porous oxide (b), prepared by electrochemical etching,
shows good corrosion resistance, but it is evidence, that porous TiO
x
layer results in signiicant increase of the corrosion resistance, with
respect to pure Ti. The corrosion current for pure Ti is higher than
for porous TiO
x
. For porous TiO
x
, a shift in the corrosion potential to
the more negative values is observed . The lower corrosion current
corresponds to better corrosion resistance of the TiO
x
than pure
