INVESTIGADORES
CERE silvia
congresos y reuniones científicas
Título:
79. Electrochemical and surface study of films formed on copper and brass at open circuit potential in slightly alkaline solutions in presence of chloride ions
Autor/es:
R. PROCACCINI,; W. H. SCHREINER; M. VALCARCE; M. VÁZQUEZ; S. CERÉ
Lugar:
Niza, Francia
Reunión:
Congreso; 61st Annual Meeting of the International Society of Electrochemistry; 2010
Institución organizadora:
International Society of Electrochemistry
Resumen:
The oxide films
growth on copper and brass (Cu77Zn21Al2) in borax 0.1 mol L-1
solution was investigated. The effect of the presence of chloride ions (0.01
mol L-1) in the electrolyte was also evaluated. Both objectives were
carried out by a set of different electrochemical, optical and surface
techniques. It was evident that Zn incorporation as an alloying element changes
the composition and thickness of the surface films resulting a more porous and
dielectric film than on copper, as was observed by several techniques as cyclic
voltammetry, differential reflectance, impedance spectroscopy and X-ray Photoelectron
Spectroscopy. Also, the formation of Cu2O/CuO duplex close to and at more positive potentials than the rest
potential (Ecorr) is evidenced as well as the fact that even at lower
potentials than Ecorr in freshly polished electrodes, in slightly alkaline
deaerated solutions at pH 9.2, the presence of Cu2O it was observed.
For brass, zinc oxides were observed at negative potentials than Ecorr, and
zincate ions near Ecorr, in good agreement to cyclic voltammetry results. By
comparing the reflectance spectra for copper and brass at open circuit
potential it was observed that brass showed lower transmittance than for copper
indicating that surface film on brass is thicker than that for copper agreeing
to potentiodynamic and chronopotentiometric curves. Within this frame, zinc
species are main constituents in surface films growth on brass at negative
potentials than Ecorr, whereas copper oxides are incorporated to surface film
near and approaching the Ecorr. Raman spectroscopy showed that Cu2O
and CuO were present in the surface films aged on both materials at OCP in
agreement to XPS spectra observed for copper and brass in borax 0.1 mol L-1
without chloride ions. The presence of chloride ions at low concentrations
contributes to oxo-hydroxides dissolution formed in the early aged stages at
open circuit potential as well as the formation of copper chloro-compounds, as
showed for Raman spectroscopy for both copper and brass electrodes. Besides, XPS
and Auger spectra showed that Cu2O and Cu(OH)2 are
observed mainly for brass aged at open circuit potential after 24 hs of
immersion in presence of oxygen, whereas ZnLMM Auger line confirm
the Zn species incorporation to surface film formed on brass.