The negative adsorption of chromium atoms on alloy-oxide film boundaries during oxidation in air and anodic passivation of Fe-Cr and Ni-Cr alloys

• Published in: Russian Journal of Physical Chemistry A Vol. 83; no. 10; pp. 1768 - 1774
• Main Authors: Andreev, Yu. Ya, Safonov, I. A.
• Format: Journal Article
• Language: English
• Published: Moscow Nauka/Interperiodica 01.10.2009
• Subjects: Chemistry; Chemistry and Materials Science; Physical Chemistry; Physical Chemistry of Surface Phenomena; Passive Film; Alloy Oxidation; Chromium Atom; Adsorption Activity; Oxide Film
• ISSN: 0036-0244; 1531-863X
• DOI: 10.1134/S0036024409100252

Equilibrium of Cr atoms between the surface layer and bulk of a binary alloy was analyzed. The Gibbs adsorption equation was used to obtain the dependence of the adsorption activity of atoms in the surface layer on their activity in the bulk. An approximate thermodynamic method was used to calculate the adsorption of Fe (Ni) and Cr atoms in the surface layers of Fe-Cr and Ni-Cr alloys. According to calculations, there was negative adsorption, X Cr ≪ 1, in the surface layer of the alloys caused by a large difference between the Gibbs surface energies of Cr and Fe (or Ni). The negative adsorption of Cr shifted chemical reaction equilibria on the alloy-oxide film boundary both in oxidation in air and in anodic passivation, 3FeO (NiO) + 2Cr = Cr 2 O 3 + 3Fe(Ni), toward oxide film enrichment in the FeO (or NiO) oxide. A unified method for calculating the composition of oxide films on alloys was used for both processes. The method was based on the use of the initial data on the Gibbs surface energy of metals constituting alloys. The calculated oxide film compositions were close to the experimental X-ray photoelectron spectroscopy data.