Abstract
A testing methodology for using Mott–Schottky (M-S) analysis to study the semiconductive properties of passive films that form on carbon steel in simulated concrete pores solutions (pH > 12.5) is presented. The development of the methodology includes determining the proper M-S potential sweep range, rate, and frequency for the passive steel, which were found to be −0.5 to 0.5 V, 18 mV/s, and 1000 Hz, respectively. The methodology was then applied to steel rebar in a saturated calcium hydroxide passivating solution (pH 12.6) to simulate the highly alkaline environments seen in concrete. Potentiostatically formed passive film was different from the film formed under open-circuit conditions. The passive film on steel rebar was found to be n-type with two discrete donor species. A donor density on the order of 1021 cm−3, a flatband potential of −0.53 V, and a maximum space charge layer thickness of 0.4 nm at full passivation were reported.
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