Multiplexed EFM Trend Purpose

This experiment allows you to follow changes (for up to eight samples) in the corrosion rate versus time. A Gamry ECM8 Multiplexer connects your Gamry potentiostat to each of the active channels in sequence. The Multiplexed EFM Trend script makes a series of Electrochemical Frequency Modulation measurements at fixed time-intervals on each of the active channels. The resulting data is very useful for metal or inhibitor screening studies and for on-line monitoring.

See the previous help sections for information concerning the EFM Trend measurement. Basically, the EFM technique is used to obtain a rapid estimate of the corrosion rate of a metal in a solution. It is particularly applicable to long-term monitoring because it involves small (<20 mV) excursions relative to Eoc. Such small excursions are less likely to change the sample than the larger voltages applied in other techniques.

EFM data, after suitable mathematical manipulation, yields an estimate of corrosion current, Icorr, which can be used to calculate a corrosion rate. Icorr is calculated directly from the EFM data. A priori knowledge of the Tafel constants is not required to find Icorr. Values of the sample’s area, density, and equivalent weight are required to convert the corrosion current value into a corrosion rate in mpy or mmpy. Although the calculation of corrosion rate does not require Tafel constants (βs), knowledge of the mechanism of corrosion is needed. Corrosion rates can be calculated assuming Activation control (Butler-Volmer kinetics), Diffusion control, or Passive Film control.