A two-step method for the evaluation of corrosion rate in metals
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We analyze the negative influence of the polarization capacity of corroding electrodes on the accuracy of evaluation of the corrosion rate. Due to the influence of deposits, the impedance of the electrode has an abnormally high capacity [(104 - 105) μF/cm2]. The difficulties encountered in measuring the polarization resistance and, hence, the corrosion rate in the process of galvanostatic polarization are caused by the uncertainty of the time of complete charging of the capacity and, hence, the time of termination of measurements. We deduce the analytic dependence of the true value of corrosion rate on various polarization currents in the process of measurements and check it with the help of an experimental model of the source of direct current with galvanostatic polarization and recording the polarization voltage on the equivalent circuit of two-electrode corrosion transducer. The results obtained by using the proposed two-step method are independent of the polarization capacity and the duration of the transition process, whereas the period of measurements is much shorter than the period of complete (98%) charging of the polarization capacity and admissible for the corrosion measurements.
Keywordscorrosion rate polarization resistance polarization capacity low-carbon steel neutral aqueous medium
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