The semiconductor properties of passive films and corrosion behavior of stainless steel reinforcing bars in simulated concrete pore solution

The vulnerability of concrete reinforcing steels to corrosion when depassivation occurs, typically in the presence of chloride, makes it important to understand the nature of the steels' passive films. In Part I of the study, electrochemical techniques and Mott-Schottky analysis were used to investigate these films formed on five different grades of stainless steel and carbon steel reinforcing bars exposed to simulated concrete pore solution. The influence of the steel composition and surface finish on Mott-Schottky plots and the electronic properties are discussed in relation to the steels' corrosion resistance. A p-type semiconductor behavior was observed in the stainless steel alloys in the cathodic potential regions and an n-type in the anodic potential regions. The n-type behavior is similar to that observed in the carbon steel. The electronic and electrochemical properties of the austenitic grades were superior to the duplex grades. The molybdenum-containing grades, 316LN and 2205, did not show the expected superior properties compared to molybdenum-free grades, 304L and 2304. Also, the replacement of nickel by manganese in the 24100 alloy was not found to be detrimental. The as-received bars showed electronic and electrochemical properties that are more realistic to field conditions than those of the polished cross-sections.