Biomedical Engineering Reference
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anodization [40]. The stress is classified into compressive
stress and tensile stress depending on the transport
number of the anion and cation in the oxides. Taking into
account that the density of Ti (
A
= 47.87) is 4.506 g·cm
−3
;
while the density of anatase (
,
an expansion factor of 1.93 can be calculated. Such high
expansion leads to crack formation in the highly stressed
regions between deep pores, due to the opposite directions
of oxidation-expansion in neighbor pores (Fig. 5.5d).
M
= 79.88) is 3.9 g·cm
−3
nanotubes
fabrication on titanium metal deposited into silicon wafer to improve
planarity: (a) compact oxide film formation, (b) breakdown of the compact
film and initial growth of wormlike pores, (c) natural selection of deeper
pores at th
e expense of shorter pores, due to their smaller available
volume for growth, and (d) conversion of pores into nanotubes by
formation of cracks as a result of expansion along the directions of
oxidation (arrows). Adapted from Refs. [38] and [39].
Figure 5.5
Schematic representation of self-organized TiO
2
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