INVESTIGADORES
ELSNER Cecilia Ines
congresos y reuniones científicas
Título:
The protection of electrogalvanized steel by passivation treatment with trivalent chromium and cobalt ions.
Autor/es:
C.R. TOMACHUK; J.D. CULCASI; C.I. ELSNER; ISOLDA COSTA; A.R. DI SARLI
Lugar:
Lausanne
Reunión:
Congreso; 65th Annual Meeting of the International Society of Electrochemistry; 2014
Institución organizadora:
ISE
Resumen:
Electroplated
zinc coatings have been largely employed as active galvanic protection for
steel substrates. However, as zinc is highly electrochemically active, its
corrosion rate may be very high. For this reason, a post treatment to increase
the lifetime of the coatings is necessary, which, in industrial practice,
consists of immersion in a chemical bath that forms a conversion layer on
plated zinc. This layer must be a dielectric passive coating with high
corrosion resistance that also offers good adherence to paints. The main
problem of conventionally used post treatments is the presence of Cr6+ salts
which are carcinogenic substances whose usage was forbidden by European
regulations. In this work the effect of trivalent chromium and Co ions in
solution of passivation treatments on the corrosion resistance of
electrogalvanised steel has been investigated in 0.1 M Na2SO4 solution by
electrochemical impedance spectroscopy (EIS) and polarization curves. Prior and
after the corrosion tests, the chemical composition and morphology of the
electrogalvanised surface was characterized by SEM and XPS. The EIS results
showed that impedance values associated to the surface with Cr3+ + Co
treatments were inferior to those exhibited by the Cr6+ treated ones. The
higher impedances related to the Cr6+ samples could be explained by the
self-healing effect of this type of coating. The SEM analyses revealed coating
cracks associated to the surface of the Cr6+ treated samples whereas for those
treated in the Cr3+ + Co solution, elongated fissures were seen. These last
samples presented inferior corrosion resistance to that of the Cr6+ passivated
ones. The cobalt addition to the trivalent chromium containing solution was not
sufficient to increase the corrosion resistance to acceptable levels in
comparison to the Cr6+ conversion coating.