Page 139 - Corrosion Engineering Principles and Practice

114 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 115

FIGURE 5.23 Commercial sensor elements to carry out linear polarization
resistance (LPR) measurements. (Courtesy of Metal Samples Company)

TCA in a 6 M HCl solution. One can first estimate the R from the
p
slopes of the polarization curves. Assuming that b and b have the
c
a
same value, that is, 0.1 mV per decade of current, each R can then
p
be converted to a corrosion current with the help of Eq. (5.22).
–355
–360
–365
–370
E (mV vs. SHE) –380
–375

–385
–390
–395
–400
–405
–2000 –1500 –1000 –500 0 500 1000
–2
Current Density (µA cm )
(a)
FIGURE 5.24 Corrosion of AISI 1018 carbon steel in 6 M HCl containing
(a) no inhibitor, (b) 250 ppm trans-cinnamaldehyde (TCA), (c) 1000 ppm TCA,
and (d) 5000 ppm TCA. The dotted line in these figures has been added to
estimate the slope of the curves that can be related to the polarization
resistance (R ).
p