Electrochemical Properties of Passive Film on Stainless Steel Surface in Nitric Acid Solution

The relationship between the corrosion resistance of 304 stainless steel and the properties of passive film on its surface at different temperatures and different concentrations of nitric acid solution was studied by polarization curve, electrochemical impedance spectrum (EIS) and Mott-Shottky curve. The results show that with the increase of temperature and nitric acid concentration, the protection and stability of the passive film on stainless steel surface reduced. The passive film forming in nitric acid solution was characterized by P-type semiconductor. XPS analysis show that the passive film was mainly composed of Cr and Fe oxides, besides high content of Cr(Ⅵ) was found in passive film generated at high temperature and high concentration of nitric acid. The changes of temperature, nitric acid concentration and the generation of some strong oxidizing ions in the passive film have different effects on the generation and dissolution rate of the passive film, which affect the corrosion resistance of the stainless steel.