Biomedical Engineering Reference
In-Depth Information
E
E
ii
exp 2.303
exp 2.303
(6)
corr
b
b
a
c
where
EEE
(7)
corr
i
11
R
1
2.303
i
(8)
t
corr
E
b
b
EE
a
c
corr
and
bb
i
i
ac
(9)
corr
2.303(
bb E
)
a
c
EEcorr
The corrosion rate in the anodic sites on the metal surface is proportional to the current
intensity. The current intensity flowing through the current cell results in change of
potentials of both anodic (oxidation) and cathodic (reduction) reactions (Hryniewicz et al.,
2009). The cathodic potential shifts into negative direction and anodic potential shifts into
positive direction.
The GPES (General Purpose Electrochemical Software) provides a convenient interface for
making Tafel plots, calculating Tafel slopes and corrosion rates. First we specify the anodic
and cathodic Tafel region. Once the regions are selected the GPES software automatically
calculates the Tafel slopes and the corrosion currents. A correct estimate of the Tafel slopes
is possible only if the linear Tafel region covers at least one decade in current. Some
additional data are the density of investigated material, equivalent mass, and the studied
surface area. Having these the algorithm serves to calculate corrosion current density,
polarization resistance, and the corrosion rate CR.
The corrosion studies of conventionally electropolished (EP) and magnetoelectropolished
(MEP) titanium samples below oxygen evolution regime were carried out in a Ringer's
solution (Table 2) at 25 C (Figs. 5, and 6). Ringer's (
Solution Ringeri
by Fresenius Kabi) and
Hank's solutions are the main artificially created human fluids generally recognized by the
researchers to carry out the corrosion studies on biomaterials.
Solution components
g/dm
3
Ions
mEq/dm
3
mmol/dm
3
Sodium chloride
8.60
Na
+
147.16
147.16
Potassium chloride
0.30
K
+
4.02
4.02
Calcium chloride
0.48
Ca
2+
4.38
2.19
Cl
156.56
156.56
Table 2. Ringer's solution composition used for the corrosion study.
