Chemisorption model of electrochemical passivity of metals and thermodynamic calculation of the flade potential of metals Ni and Cr taking into account their surface Gibbs energy

• Published in: Protection of metals and physical chemistry of surfaces Vol. 51; no. 5; pp. 730 - 739
• Main Authors: Andreev, Yu. Ya, Bobkov, T. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.09.2015; Springer Nature B.V
• Subjects: Activation; Adsorption; Characterization and Evaluation of Materials; Chemisorption; Chemistry and Materials Science; Chromium; Corrosion and Coatings; Critical point; Energy; First principles; Free energy; Heat of formation; Hypotheses; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Mathematical models; Metal oxides; Metallic Materials; Metals; Nickel; Passivity; Physical chemistry; Physicochemical Processes at the Interfaces; Sulfur; Surface chemistry; Surface energy; Surface layers; Tribology; KSCN; Passive State; Passive Film; Standard Gibbs Energy; Gibbs Energy
• ISSN: 2070-2051; 2070-206X
• DOI: 10.1134/S2070205115050032

A model of the chemisorption passivity of metals based on the consideration of equality of the electrochemical potentials of the metal ion at the interfaces between the bulk of a metal, the monoatomic surface layer (SL) of a metal, and the surface metal oxide has been proposed. Thereby, unlike the Vetter model, this approach takes into account the occurrence of the Galvani potential of the metal atoms (ions) in the SL in the form of the surface Gibbs energy Δ G S ( hkl ) of a particular crystal face. On this basis, a formula of the Flade potential E F(S) of a metal has been derived; this formula, along with the chemical Gibbs energy of formation of oxides, makes allowance for the Δ G S ( hkl ) value (of a low-index face of the metal). Normal potential E F(S) 0 (a pH of 0) has been calculated using the data of the first-principle calculation of the surface energy of metals. The calculated E F(S) 0 values of 0.46 and−0.19 V for Ni and Cr, respectively, are in good agreement with the literature data. The calculated E F(S) values and the critical points in the anodic curves of passivation and activation of nickel in a 0.5 M H 2 SO 4 solution and in the presence of KSCN additives have been compared.