On the conduction mechanisms of passive films on molybdenum-containing stainless steel

The effects of alloying with molybdenum to 18Cr-10Ni steel were studied by analyzing the conduction mechanisms through the passive films. Current-voltage characteristics were obtained from measurements conducted on steel-passive film-metal structures. It was shown that the conduction mechanism was interface controlled and that the passive film could be considered as an n-type semiconductor. In this respect, a reduction of the donor density was related to the effect og molybdenum. The measurements of the capacitance and its frequency of voltage dependence further indicated that the mobile positive charge density was lowered when molybdenum was alloyed to the stainless steel (SS). On the basis of these results, a mechanism was proposed to demonstrate how molybdenum lowered the conductivity of the passive film, considering the results in the literature on the passivity of SSs