Biomedical Engineering Reference
In-Depth Information
FIGUre 12.9
fracture fixation plate and screws.
It is not uncommon to observe crevice corrosion in modular devices.
In conjunction with stress corrosion processes, it can potentially decrease
the life of metals subject to cyclic loading. The possibility of crevice
corrosion, either in physical cracks or in crack-like defects in a passiv-
ation layer, may lead to the abolition of the fatigue endurance limit for
metallic alloys. This is a particular challenge for iron-base alloys, such
as the stainless steels. This latter situation is sometimes called
fatigue
corrosion.
Pitting corrosion
This is a special case of crevice corrosion. It is a more isolated, sym-
metric form of attack (Figure 12.10). Inclusions, scratches, or handling
damage may initiate it. It proceeds through processes similar to crevice
corrosion, although static (non-flow) conditions and oxygen depletion
seem less important. The cathodic reaction shown is the most prob-
able complete one
in vivo
near neutral pH in well-vascularized tissue.
2 H
2
O
O
2
(d) + 4H
+
4 e
-
(Cl
-
)
(M
+
)
4 M
+
FIGUre 12.10
Pitting corrosion.
Search WWH ::
Custom Search