Biomedical Engineering Reference
In-Depth Information
Figure 9.26
SEM images of the anodic ilm with a layered structure on
silicon carbide substrate [118].
Anodization of Ti is not limited to dental or orthopedic implant
surfaces only. The process can be applied to dental arch wire, too
[110], resulting in nanosurface topography. The arch wire provides
torsion and bending forces, and through the brackets, the forces
are exerted on the teeth. Stainless alloys, NiTi-based alloys, and
β-Ti-based alloys are most widely used materials for the dental
arch wires [103, 110]. NiTi-based alloys and β-Ti-based alloys are
the shape memory alloys and have unique super elastic properties
[70, 72]. By carefully choosing the anodization conditions, the arch
wires can be produced with red, yellow, green, and other kinds of
colors. The colors of the wires are caused by light interferences
through the oxide layers, indicating oxide thickness. Yang
et al
.
[110] used different electrolytes for respective surface preparation.
They applied 1M H
2
SO
4
, 1M H
3
PO
4
, 3 wt% Na
2
SO
4
· 10H
2
O, and
5 wt% Na
3
PO
4
· 12H
2
O. The anodization was conducted at 10-60 V,
and at a constant temperature of 25°C. The anodization time was 1
and 10 min for the β-Ti wires, and 120 min for the NiTi wires. The
colors of the anodized wires vary with the applied voltages, and
the wires of a wide spectrum of colors were obtained (Fig. 9.27,
Fig. 9.28). The TiO
2
layers are found on both kinds of anodized wires,
and no nickel element was detected on the surface of the anodized
NiTi wire [110]. The thickness of the oxide layers increases, with the
increasing voltages and time of anodization (Table 9.1). The oxide
layer is uniformly formed on the anodized β-Ti wires, but the surface
roughness of the NiTi wires increases after anodization (Fig. 9.29).
The NiTi wires are not as bright as the β-Ti wires, which is related
to oxide layer uniformity (more uniform for β-Ti wires). Since
anodization only modiies the surfaces, the tensile properties of both
the two anodized wires remain unchanged [110].
