Biomedical Engineering Reference
In-Depth Information
of chloride ions (Table 5.1) and their ability to induce localized
corrosion. Another factor is the body temperature, close to 37°C,
which is enough to accelerate electrochemical reactions or even
changes in the mechanism of corrosion, which can be different at
room temperature [52]. Body luids also contain different types of
biomolecules and cells, which may attach to the biomaterial surface
and affect the surface reactions [52].
Table 5.1
Typical chemical composition of human blood plasma [52]
Concentration (mmol
⋅
L
-1
)
Ion
Na
+
142.0
K
+
5.0
Mg
2+
1.5
Ca
2+
2.5
Cl
−
103.0
HC O
3
−
27.0
HP O
4
2−
1.0
S O
4
2−
0.5
The corrosion can be classiied into the following types (Fig. 5.2)
[6, 10, 22, 51]:
(i) Uniform corrosion is deined as a chemical or electrochemical
reaction that proceeds uniformly over the exposed surface.
(ii) Galvanic corrosion occurs due to the galvanic coupling of
two or more different metals in the voltage range (Fig. 5.1).
Less corrosion-resistant metal become anode and undergo
corrosive attack.
(iii) Crevice corrosion causes the regions of stagnant solutions,
which attacks the material through enhanced local ions lux.
(iv) Pitting is a localized corrosion that results in breakdown of the
protecting passive layer and holes formation on the surface.
(v) Intergranular corrosion occurs through the grain boundaries,
because of theirs higher reactivity (anode area) with respect
to the grains (cathode area).
(vi) Selective corrosion (dealloying) results in removal of one
element (more anodic with respect to the second one) from a
solid alloy by corrosion process.
(vii) Erosion corrosion occurs when a relative movement between
a corrosive luid and the material surface is present, which
