The Determination of the Corrosion Rate of Zinc in Solution by the Differential Pulse Method

The electrochemical measurement of the corrosion rate of zinc in near-neutral solutions using a differential pulse polarograph as been achieved to a greatly improved accuracy compared with previous w~rk. The perturbation of the corroding system is minimized as the potentiostatic polarizing pulse is applied for only 60 msec. The double layer charging of the electrode is moni-tored on an oscilloscope and the faradaic urrent measurements made by the normal Y recorder output of the polarograph. The iR correction facility on the polarograph is used to determine the Tafel parameters and can also be used if resistance overvoltage is a problem during the polarization resistance mea-surements. Four different solutions are examined where the cathodic processes are either separately or jointly oxygen reduction or hydrogen evolution. Where only one cathodic process occurs, the correlation of the weight loss with the corrosion current calculated by the Stern-Geary method is within 7%. Where two cathodic processes occur, errors of up to 15 % are encountered.