GALVANOSTATIC RESPONSE OF THE PASSIVE FILM ON IRON IN ACID-MEDIA

The galvanostatic technique applied to the passive system enables access to be made to the region between zero current and the steady state passivation current in the potentiostatic polarization diagram. It permits visualization of the electric field apploed to the passive film out of its steady state value. A good correlation with the impedance behavior of the passive iron is observed in the entire frequency range. The long time domain of the potential/time curves reveals an exceptional degree of linearity in a wide range of current applied. In this region the passive film may be represented by a capacitor whose charge is defined not only by the applied potential but also by the actual film thickness. The hydrodynamic conditions affect the galvanostatic transient in the case of the Fe/H//3PO//4 passive system.