SEMICONDUCTING PROPERTIES OF PASSIVE FILMS FORMED ON STAINLESS-STEELS- INFLUENCE OF THE ALLOYING ELEMENTS

Passive films formed on stainless steels in a berate buffer solution ( pH 9.2) have been investigated by capacitance measurements and photoel ectrochemistry. The study was carried out on films formed on AISI type 304 and 316 stainless steels and high purity alloys with differing ch romium, nickel, and molybdenum contents. Complementary research by Aug er analysis shows that the passive films are composed essentially of a n inner chromium region in contact with the metallic substrate and an outer iron oxide region developed at the film/electrolyte interface. T he semiconducting properties of the passive films are determined by th ose of the constituent chromium and iron oxides which are of p-type an d n-type, respectively. Thus the influence of the alloying elements on the semiconducting properties of the passive films is explained by ch anges in the electronic structure of each of these two oxide regions.