A comparative study of semiconducting behavior of passive film of high nitrogen and Ni and Mn free stainless steels in 3.5 wt. % NaCL

Abstract

The semiconducting property of passive films formed on Alloy 1 (18Cr-2Mo-1N), Alloy 2 (17.5Cr-3Mo-0.5N) and Alloy 3 (Type 316 SS) were studied by using the Mott-Schottky (M-S) approach in 3.5 wt. % NaCl solution of pH 2, 7 and 12. The M-S analysis shows that the film acts as n-type and p-type semiconductors across the potential range. The donor density of Alloy 1 has been found to be lower by about 31%, 11% and 6% as compared to that of Alloy 2 at pH 2, 7 and 12 respectively. However, Alloy 3 has higher donor density 44%, 27% and 30% in comparison with Alloy 1. The donor density of Alloy 3 found to be greater about 21%, 18% and 25% to the Alloy 2 at pH 2, 7 and 12 respectively.These results indicate that the sensitivity of electrolyte composition and the presence of alloying elements like nitrogen and nickel on the donor density of passive film. High nitrogen stainless steels exhibited a lower donor density that corresponds to good protectiveness, more stable passive film which is in agreement with a low passive current density (i<inf>pass</inf>), higher pitting potential (E<inf>pit</inf>) and polarization resistance (R<inf>p</inf>). © (2013) Trans Tech Publications, Switzerland.