MOTT-SCHOTTKY INVESTIGATION OF THE PASSIVE FILM ON REBAR IN CONCRETE

摘要

The rebar in concrete is under passivated due to the high alkali environment of concrete. The electrochemical behavior of passive film is related to its semiconductor nature. Saturated Ca(OH)2 solutions were used to simulate concrete pore solutions, in which the semiconductor characteristics of passivation film on rebar were investigated by Mott-Schottky (M-S) plots. It is shown that in the potential region of -0.78 to 0.37 V the passive film of rebar in concrete is of highly disordered n-type semiconductor and the donor density is in the order of 1026m-3. The capacitance is dependent on frequency which result in strong dispersion of the M-S plots. In the presence of chloride (wt.Cl- %, < 0.2%) in system solutions, the slope of M-S plot decreased apparently, showing that chloride ion is to cause passive film corrosion and breakdown. Although M-S plots of passive film on rebar embedded in concrete with or without various mineral admixtures are similar to that in simulated system solution, introduction of proper quantity admixtures in concrete could lead to the thicker space-charge layer and thus the thicker passive film layer.