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Gamry introduced the EFM140
Electrochemical Frequency Modulation Software in 2004. The EFM140 makes
Electrochemical Frequency Modulation (EFM) commercially available for the
first time.
What is EFM?
EFM is an electrochemical technique in which two sinusoidal potential
signals are summed and applied to a corrosion sample through a
potentiostat. The resulting current is measured and the time-domain data is converted to the
frequency domain to measure the signal at the applied fundamental
frequencies, at harmonics of the fundamental frequencies, and at
intermodulation frequencies.
What Are the Advantages of EFM?
By the appropriate mathematical manipulation, EFM gives the corrosion
engineer a great deal of useful information, including:
1. Corrosion Rate
2. Tafel Constants
3. A causality factor to validate the data
Unlike Polarization Resistance experiments, Tafel Constants are not needed
to calculate the corrosion rate with EFM. The measurement of Tafel
Constants during the EFM experiment is a bonus that can have
significant implications. For example, by monitoring the Tafel
Constants, it may be possible to determine if the mechanism of corrosion
is changing during a long-term corrosion study, such as inhibitor
evaluations.
Also, the acquisition of sufficient EFM data to calculate a corrosion rate
requires only 2-10 minutes! And since the amplitude of the
AC voltage waveform is only 10-20 mV, EFM is considered to be a
non-destructive technique. In this respect, EFM is similar to
Polarization Resistance and Electrochemical Impedance Spectroscopy.
How Was EFM Developed?
EFM started with the Butler-Volmer
equation, so EFM is well-founded in established corrosion theory. EFM was
developed at the University of Leuven by Dr. Walter Bogaerts and his
students, with support from EPRI. Publications detailing the theory of EFM are below:
“Electrochemical Frequency Modulation: A New Electrochemical Technique
for Online Corrosion Monitoring”, R.W. Bosch, J. Hubrecht, W. F.
Bogaerts, and B.C. Syrett, Corrosion, 57 (2001): p. 60.
“Instantaneous
Corrosion Rate Measurement with Small-Amplitude Potential Intermodulation
Techniques”, R. W. Bosch and W. F. Bogaerts, Corrosion, 52 (1996): p.
204.
Studies suggest that results from EFM compare well with polarization
resistance, EIS, and weight loss, but the number of systems that have been
evaluated thus far are very limited. It will be interesting to see how EFM
performs in a wider range of applications.
How Does the EFM140 Software Work?
If you're a Gamry user, the EFM140 is easy to implement. The EFM140
Electrochemical Frequency Modulation Software can control any Gamry Potentiostat. The
price of the EFM140 is less than $550.
How Does EFM Compare to Other
Techniques?
A quick comparison in our labs of corrosion
rates measured by EFM, LPR, and EIS shows excellent correlation.
The staff at the 2004 Penn State
Corrosion Short Course compared EFM, LPR, EIS, and Tafel Plots for the
measurement of the corrosion rate of iron in sulfuric acid. The
results are here.
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