engleski

Impedance of anodically passivated Fe80B20 glassy alloy in solutions of various pH

Anodic passive films grown on the glassy alloy Fe80B20 under strongly controlled conditions are characterized by an impedance technique in solutions of different pH (7.4-12.1) and potentials covering passive and begining of the oxygen evolution reaction (OER) regions. Modellizations of the passive film/solution (F/S) interface region is proposed on the basis of shapes of Bode plots and Mott-Schottky dependences. Semiconductor behaviour due to the oxygen nonstoichiometry with Nernstian pH dependence is obtained over almost the whole passive potential region. Passive current densities independent of the electrolyte pH indicate that the corrosion current is determined by a pH independent electric field strength within the space-charge layer. At higher anodic potentials and higher electrolyte pH, due to the surface deprotonation reaction, there is an increased density of basic (MOH^-) surface groups acting as surface states, and reactants in the first step of OER. Further increase in anodic potential facilitates surface oxidation of (MOH^-) to (MOH^o). In the OER potential region, the passivated Fe80B20 electrode acts as a classical oxygen electrode. Comparison of the data with those obtained on the pure Fe passivated under the same conditions, shows the detrimental effect of B on either the corrosion properties of the passive film in the passive potential region, or on the parameters of OER.

Glassy alloy Fe80B20 ; Fe-based anodic oxide films ; passive films ; impedance

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