MOTT-SCHOTTKY ANALYSIS OF PASSIVE FILMS AND CORROSION BEHAVIOR OF TYPE 316LN STAINLESS STEELS

摘要

The passive films formed on type 316 LN stainless steels were investigated by capacitance measurement using the Mott-Schottky (MS) approach. The passive films were potentiostatically formed in acidic (1 N H_2SO_4), acidic chloride (1 N H_2SO_4 + 0.1 M NaCl), and in neutral chloride (0.1 M NaCl) media. In the capacitance measurement, the nitrogen content of the alloy and the concentration of the electrolyte does not affect the estimated donor and acceptor densities of the n-type and p-type of the passive oxide layers. The decrease in flat band potentials decreasing with increasing nitrogen content was observed. The assessments of pitting corrosion resistance in acidic chloride (1 N H_2SO_4 + 0.1 M NaCl) and in neutral chloride (0.1 M NaCl) media were carried out at room temperature. In the acidic chloride media, the passive film current density decreases with increase in nitrogen content with secondary passivation potential In 0.1 M NaCl solution, the pitting resistance was found to increase with increase in nitrogen content. Based on the results obtained, an attempt was made to correlate the electronic properties of the passive films with pitting corrosion resistance.