Electrochemical and Semiconducting Properties of Passive Films on Steel Surfaces in Alkali-Activated Slag Extraction Solution

Abstract

The purpose of this paper is to investigate the electrochemical and semiconducting properties of passive films on steel surfaces in alkali-activated slag extraction solution (NSAS) using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and Mott-Schottky (M-S) analysis. The diffusivity of point defects (D) in the passive film on steel surfaces in NSAS, based on the point defect model (PDM) theory, was calculated for the first time. Passive film on steel surfaces in an ordinary portland cement extraction solution (OPCS) was also studied for comparative purposes. The results show that steels in NSAS and OPCS all show typical passive system features. Passive film on steel surfaces in NSAS was thicker than that in OPCS at the same film formation potential. All the passive films in this paper were n-type semiconductors, and the donor density of the passive film in NSAS was on the order of 119–12 cm−3, and that of passive films in OPCS was on the order of 12 cm−3. The D of steel in NSAS was lower than that in OPCS. The EIS analysis, M-S analysis, and calculation of D all supported the same conclusion: passive film on steel surfaces in NSAS was more protective than that in OPCS.