ELECTRODE IMPEDANCE STUDIES OF STEEL IN NEUTRAL SULFATE-SOLUTIONS, COVERED WITH AN OIL COATING CONTAINING A NITRATED PETROLEUM-PRODUCT

The mechanism of interaction of a nitrated petroleum product with steel was studied by the impedance technique. Steel electrodes were covered with an oil coating containing a nitrated petroleum product and completely immersed in a not de-aerated solution of K2SO4. The electrode impedance was interpreted quantitatively in terms of finding individual elements of a model which is likely to describe a real system best. By means of numerical methods it has been shown that the studied system can be described by the model with two time constants, which contains a constant phase element (CPE) instead of a capacitor. On the basis of experimental results it was established that the high anticorrosive effectiveness of the coating can be attributed to the mechanism of action, which is based, at the beginning, on the complete blocking of the surface. While penetration of the coating and the protective film by the electrolyte proceeds the barrier action recedes and further protection is preserved due to hindering of electrode reactions.