Biomedical Engineering Reference
In-Depth Information
The inluence of luoride and chloride ions on the corrosion
behavior of Ni-Ti orthodontic wires was studied by Li
et al
. [28]. The
results indicates that Ni-Ti alloy is primarily susceptible to localized
corrosion when exposed to a solution containing chloride, while
it is susceptible to general corrosion when subjected to a solution
containing luoride.
The effects of chloride and luoride on NiTi wires are listed in
Table 5.4. Ni-Ti orthodontic wires exhibit better behavior in chloride
than luoride solution. Ni-Ti in luoride solutions does not passivate
due to the large magnitude of the anodic current density. Ni-Ti
orthodontic wires are susceptible to pitting corrosion in chloride
solutions. The combination of luoride and chloride signiicantly
deteriorate the corrosion resistance of Ni-Ti alloys, with comparison
to those in individual luoride or chloride solutions [28].
Table 5.4
Results of potentiodynamic measurements of NiTi alloy in
solutions [28]
Concentration
(mol L
-1
)
E
corr
(mV/CE)
I
corr
(μA cm
-2
)
I
passive
(μA cm
-2
)
Solution
type
1.865 (0.396) × 10
3
NaF
0.0238
-430 (18) 96.5 (30)
5.227 (0.116) × 10
3
0.0476
-442 (20) 162 (22)
8.080 (0.453) × 10
3
0.0714
-428 (36) 160 (18)
16.27 (0.907) × 10
3
0.1538
-439 (36) 215 (13)
NaCl 0.0238
-171 (37) 0.026 (0.014) 0.623 (0.339)
0.0476
-106 (27) 0.049 (0.007) 0.940 (0.142)
0.0714
-105 (925) 0.013 (0.003) 0.520 (0.075)
0.1538
-161 (3) 0.035 (0.005) 0.353 (0.083)
NaF +
NaCl
0.0119 NaF +
0.0119 NaCl
-235 (9) 2.1 (1.4)
185 (978)
-390 (11) 84.1 (24.4) 3.38 (1.252) × 10
3
0.0238 NaF +
0.0238 NaCl
14.79 (8.287) × 10
3
0.0714 NaF +
0.0714 NaCl
-448 (11) 140 (33)
Note:
Standard deviations are given in parentheses.
The surface morphology after the cyclic polarization test in the
mixed solutions containing 0.0714 mol/L NaF and 0.0714 mol/L
NaCl indicated, that both pitting and general (uniform) corrosion
occurs (Fig. 5.16) [28].
