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Determination of the Chemical Potentials of Highly Supersaturated Cu-Co Alloys

Published online by Cambridge University Press:  15 February 2011

F. Gärtner ,
R. Busch ,
P. Haasen  and
R. Bormann
F. Gärtner
Affiliation:
Institut für Metallphysik, Hospitalstrasse 3-7, D-37073 Göttingen, F.R. Germany
R. Busch
Affiliation:
Institut für Metallphysik, Hospitalstrasse 3-7, D-37073 Göttingen, F.R. Germany
P. Haasen
Affiliation:
Institut für Metallphysik, Hospitalstrasse 3-7, D-37073 Göttingen, F.R. Germany
R. Bormann
Affiliation:
GKSS Research Centre, Institute for Materials Research, Max-Planck-Strasse, D-21502 Geesthacht, F.R. Germany
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Abstract

With the CALPHAD approach based on the regular solution model, the thermodynamic functions of the Cu-Co system can be extrapolated to compositions where the homogeneous fee solid solution is thermodynamically unstable. Up to now it has been unclear how reliable such extrapolations are in view of the driving forces for decomposition and whether the Gibbs energy is well described by the model in the unstable region. Therefore, electromotive force measurements were performed to determine directly the chemical potentials of highly supersaturated Cu-Co alloys. Under the prerequisite that time scales of the electrochemical exchange reaction are fast compared with the kinetics of decomposition, the thermodynamics of the alloys can be investigated quasi statically. Within the experimental accuracy the results for both a metastable and an unstable alloy agree well with the calculated chemical potentials. In addition, the experiments demonstrate that the electrochemical cell reaction is reversible upon small external concentration fluctuations of the investigated alloys. Possible reasons for this unexpected stability are discussed taking the kinetics of the decomposition into account.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 400: Symposium E – Metastable Metal-Based Phases and Microstructures , 1995 , 119
Copyright
Copyright © Materials Research Society 1996

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