Biomedical Engineering Reference
In-Depth Information
the generation of oxygen vacancies at the metal/barrier oxide
interface, the repelling forces of the cation vacancies results in
separation of the neighboring pores leading to individual nanotubes
[74]. Addition of bromide or chloride ions to H
3
PO
4
electrolyte
initiates pitting, but did not result in nanopores [74]. The electrolyte
must be acidic (with HF or NaF addition) to form ordered nanopores
layer.
Figure 9.45
Separation of nanopores to form individual nanotubular
oxide layer during anodization of Ti: (a) formation of
individual nanotubes during anodization, (b) side-view of
the nanotubes after anodization, (c) schematic illustration
of pore separation mechanism. Cation vacancies generated
by dissolution of Ti cations are transported radially from the
two sides of common wall of the neighbor pores. Charges of
similar polarity repel and when electrical neutrality is not
maintained this repulsion causes separation of pores into
individual nanotubes [74].
Oh [85] produced vertically aligned TiO
2
nanotubes on Ti sheet
(0.25 mm thick, 99.5% purity) using anodization technique at
20 V for 30 min in electrolyte consisting 0.5% HF in water.
Titanium oxide nanotubes were then chemically treated with
NaOH solution to enhancing theirs bioactivity. In chemical treatment,
