Study on the adsorption of OH− and CaOH+ on Fe (100) surface and their effect on passivation of steel bar: Experiments and DFT modelling

Abstract The differences in the formation mechanism of passivation films of steel bar in Ca(OH)2 and NaOH solutions were studied by experiments and DFT simulations. The electrochemical tests indicate that the stability of passive film formed in Ca(OH)2 solution is greater than that in NaOH solution. In Ca(OH)2 solution, not only OH− but also CaOH+ adsorb on the iron surface and cause the zeta potential shift from negative to positive. The interaction of Fe (100) surface with CaOH+ is stronger than NaOH, and the adsorption of CaOH+ decreases the spin value of Fe and thereby being unfavorable to adsorption of O2.