Determining the partial currents of silver ionization, its oxide formation, and chemical dissolution by multicycle chronoammetry with an RRDE

• Published in: Protection of metals 2008-05, Vol.44 (3), p.301-309
• Main Authors: Kudryashov, D. A., Grushevskaya, S. N., Vvedenskii, A. V.
• Format: Article
• Language: English
• Subjects: Anodic; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Discs; Disks; Dissolution; Electrodes; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Investigation Methods for Physicochemical Systems; Ionization; Materials Science; Metallic Materials; Oxides; Silver; Tribology
• ISSN: 0033-1732; 2070-2051; 1608-327X; 2070-206X
• DOI: 10.1134/S0033173208030144

A multicycle chronoammetry with a rotating disc electrode with a ring (RRDE) enables one to experimentally discriminate between the partial currents of the substrate metal ionization, anodic formation of the oxide, and chemical dissolution of the oxide in the summary polarization current of the disc. The technique is approved by an example of Ag|Ag 2 O|OH − (H 2 O) system. In a range of relatively small anodic potentials of the Ag disc (0.48 to 0.51 V), the active dissolution of silver at the open surface sites and via pores in the surface film dominates; the phase formation current and, accordingly, the current efficiency of the process rapidly drop. At the potentials of the voltammogram maximum (0.52 to 0.53 V) when the silver active dissolution current is suppressed, the phase formation currents prevail and substantially exceed the chemical dissolution rate of the oxide. The thickness of an Ag 2 O film rapidly increases under these conditions, and the current efficiency of the oxide formation is close to 100% for the whole polarization period. The rate constant of the chemical dissolution of an Ag(I) oxide is practically independent of the anodic phase-formation potential, but slightly depends on the oxide film thickness, reflecting changes in the film structure and, possibly, in its composition, from AgOH to Ag 2 O.