Biomedical Engineering Reference
In-Depth Information
Kahan et al . [25] investigated the wear of the Ti-alloys in the
presence of corrosive environments. The Ti-13Nb-13Zr alloy is
more corrosion resistant than Ti-6Al-7Nb and Ti-6Al-4V whereas
in the presence of protein, the corrosion resistance of Ti-13Nb-13Zr
and Ti-6Al-7Nb is reduced with respect to Ti-6Al-4V [25]. In the
presence of the corrosion and wear, the corrosion resistance of Ti-
13Nb-13Zr is higher than Ti-6Al-7Nb or Ti-6Al-4V in phosphate-
buffered-saline. In the presence of proteins, the corrosion resistance
of Ti-13Nb-13Zr and Ti-6Al-7Nb is higher than that of Ti-6Al-4V
[25]. The wear of Ti-13Nb-13Zr is lower than that of Ti-6Al-7Nb
and Ti-6Al-4V with or without the presence of proteins in a corrosive
environment and hence overall degradation when both corrosion
and wear processes occurs is lowest for Ti-13Nb-13Zr and highest
for Ti-6Al-4V. The presence of proteins reduces the degradation
of all three alloys [25]. The increased corrosion resistance of the
Ti-13Nb-13Zr is due to the fact that Nb and Zr are less soluble than
Al and V, and that the passive oxide layer on the surface of the alloy is
more inert, because it consists of surface rutile structure [4, 25, 43].
The toxic effect of Ni on the tissue in the Ti-alloys (with Ni) can
be reduced by anodization [47]. Anodization of Ni-Ti alloy in acetic
acid improves corrosion resistance in Hanks' solution with respect
to untreated NiTi (Fig. 5.10). The Ni/Ti atomic ratio at the surface is
very much reduced after anodization, with a value of 0.04 versus that
Figure 5.10 Cyclic polarization curves of bare NiTi and anodized NiTi;
Hank's solution at pH = 7.4 and 37°C [47].
 
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