ELECTRONIC PROPERTIES AND PITTING SUSCEPTIBILITY OF PASSIVE FILMS ON FERRITE AND PEARLITE IN CHLORIDE-CONTAINING SOLUTION

摘要

A comparison of electronic properties and pitting susceptibility between ferrite and pearlite has been made by using electrochemical noise analyses, anodic polarization measurements and Mott-Schottky analyses. It was found that, in 0.01M Na_2CrO_4 + 0.05M NaCl solution, ferrite is more susceptible to pitting than pearlite: ferrite has a higher standard deviation of current fluctuations, a higher metastable pitting rate and a lower passive film breakdown potential than those on pearlite. These differences are explained by the electronic properties obtained from Mott-Schottky analyses. The passive films on both ferrite and pearlite in 0.01M Na_2CrO_4 solution are highly disordered n-type semiconductors with two donor levels: shallow and deep. However, the passive films on ferrite have higher donor concentrations than those on pearlite. A galvanic effect occurred when ferrite and pearlite coupled together in chromate solution containing chloride ions with ferrite as the anode.