Page 149 - Corrosion Engineering Principles and Practice

124 C h a p t e r 5 C o r r o s i o n K i n e t i c s a n d A p p l i c a t i o n s o f E l e c t r o c h e m i s t r y 125

Imaginary Axis Point 3

Point 2

Point 1

Real Axis
R s
(R + R )
p
s
FIGURE 5.28 Schematic of the extrapolation method to obtain the polarization
resistance from EIS data.

which allows for a single data logger to monitor multiple devices in
the same general vicinity [Fig. 5.29(a) and (b)] [20].
The wireless EIS sensor determines the impedance at 15 to
20 independent frequencies, by measuring amplitude and phase at
each frequency (Fig. 5.30). It computes corrosion rate, conductivity,
and coating impedance and transmits the result wirelessly to a data
logger. The miniature and wireless features make it suitable for
embedding in concrete or placing in hidden and inaccessible locations,
for example, in HVAC systems. Its minimal power consuming aspect
lends itself useful for long-term monitoring of coating integrity. The
miniature EIS system has been tested in various environments,
namely concrete, water, and under coatings [Fig. 5.31(a) and 5.31(b)].

Electrochemical Noise Analysis
Fluctuations of the corrosion potential of a corroding metallic
specimen are a well known and easily observable phenomenon.
Electrochemical noise analysis (ENA) as a corrosion tool has
increased steadily since Iverson’s paper in 1968 [21]. The study of