THERMODYNAMIC CALCULATION OF THE FLADE POTENTIAL OF METALS Fe, Ni, AND Cr TAKING ACCOUNT OF THEIR SURFACE GIBBS ENERGY

摘要

A method for the thermodynamic estimation of the active-passive transition potential of metals (Flade potential) in sulfuric acid (pH 0) is proposed. This theoretical calculation of the Flade potential (E~0_F) differs from the conventional one in that the Gibbs formation energy of the metal oxide on the surface △G~0_Me/Ox is a sum of the Gibbs formation energy of the oxide △G~0_T＜ 0 and the surface Gibbs energy of the metal △G~0_ S,me> 0. The technique of△G~0_ S,meestimation used is based on the concept of the self-adsorption of metal, atoms (A) in the superficial layer and obeys the Gibbs adsorption equation σ = -ΓA△μA. The estimated Flade potentials of Ni, Cr, and Fe agree with the known experimental data.