Instantaneous corrosion rate measurement with small-amplitude potential intermodulation techniques

With the intermodulation technique, a potential distortion using two sine waves is applied to a corrosion system. The alternating current (AC) response consists of amplitudes measured at different frequencies. Simple relations are derived from the current-vs-potential relation for a corroding process under activation control, from which the corrosion rate and Tafel parameters can be calculated. These are valid when the amplitude of the applied potential distortion is sufficiently small. With the intermodulation technique, the corrosion rate and Tafel parameters can be obtained within one measurement, which makes this technique an ideal candidate for application as a corrosion monitoring tool. Results obtained with this technique were shown to be in agreement with other electrochemical methods for corrosion rate measurement, such as Tafel extrapolation, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS).