Biomedical Engineering Reference
In-Depth Information
in comparative studies, which leads to the accepted methods of
research in the laboratory, and approximately simulating real
biological environment. These methods allow the determination of
such values as corrosion potential, corrosion current density, and
polarization.
The polarization data obtained for Ti-HA nanocomposites and
microcrystalline titanium, including corrosion potentials (
E
C
),
corrosion current densities (
i
C
), and corrosion rate (
C
R
) values are
summarized in Table 7.3. From this table it is possible to observe
that hydroxyapatite doped to titanium had a positive effect on
corrosion resistance of Ti. The corrosion test results indicate that
the microcrystalline titanium possesses lower corrosion resistance
and thus higher corrosion current density in Ringer's solutions. The
result indicated that there was no signiicant difference in corrosion
resistance among Ti-3 vol% HA (
i
C
= 9.06 × 10
-8
A/cm
2
,
E
C
= -0.34 V
vs. SCE) and Ti-20 vol% HA (
i
C
= 8.5 × 10
-8
, A/cm
2
,
E
C
= -0.55 V vs.
SCE) although there was a signiicant difference in porosity. The
polarization curves (Fig. 7.7) of these nanocomposites had a wider
passive region, which can provide an excellent corrosion resistance,
even if the applied potential rises to 850 mV vs. SCE for Ti-20 vol% HA
and to 2500 mV vs. SCE or higher for Ti-HA (3, 10 vol%) composites.
For Ti-20 vol% HA, the current density in the passive range is 2
and 1 orders of magnitude smaller than for Ti-10 wt% HA and Ti-3
vol% HA, respectively. Besides, the hydroxyapatite reinforced with
titanium decreased about hundredfold the corrosion rate of Ti.
Corrosion tests show that the modiication of microstructure
of titanium by hydroxyapatite signiicantly improves the corrosion
resistance. The rate of corrosion is affected, inter alia, by the density
of the material. Although the obtained nanocomposites possess
certain porosity, corrosion rate decreases.
Table 7.3
Mean values of corrosion current densities, corrosion
potentials and corrosion rate of Ti-HA nanocomposites and
microcrystalline titanium (grade 4) in Ringer's solutions
i
C
(A/cm
2
)
Materials
E
C
vs SCE
(V)
C
R
(mm/year)
9.06 × 10
-8
Ti-3 vol% HA
-0.34
0.003
Ti-10 vol% HA
1.19 × 10
-7
-0.41
0.004
Ti-20 vol% HA
8.5 × 10
-8
-0.55
0.003
Ti (microcrystalline) 1.31 × 10
-5
-0.36
0.363
