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Selective Dissolution in Copper-Tin Alloys: Formation of Corrosion-Resistant Patina on Ancient Chinese Bronze Mirrors

Published online by Cambridge University Press:  10 February 2011

Michelle Taube ,
Alison J. Davenport ,
Alexander H. King  and
W. Thomas Chase III
Michelle Taube
Affiliation:
University of New York at Stony Brook, Department of Materials Science and Engineering, Stony Brook, NY 11794-2275 Brookhaven National Laboratory, Department of Applied Science, Upton, NY 11973-5000
Alison J. Davenport
Affiliation:
Brookhaven National Laboratory, Department of Applied Science, Upton, NY 11973-5000 University of Manchester/UMIST, Manchester Materials Science Centre, Manchester Ml 7HS, United Kingdom
Alexander H. King
Affiliation:
University of New York at Stony Brook, Department of Materials Science and Engineering, Stony Brook, NY 11794-2275
W. Thomas Chase III
Affiliation:
Freer Gallery of Art, Department of Conservation and Scientific Research, Smithsonian Institution, Washington, DC 20560
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Abstract

Many ancient Chinese bronze mirrors have survived with a patina that leaves the delicate relief surface decorations intact. The microstructure of these ancient mirrors is two-phase and consists of acicular α-phase (Cu-rich) regions encased in a δ-phase (Sn-rich) matrix. At the surface, there is evidence of selective dissolution of the α-phase; the α-phase regions are replaced pseudomorphically by a mineral product with the δ -phase remaining metallic. Electrochemical polarization has been used to drive the copper dealloying process in modern, cast bronze. Synchrotron x-ray diffraction was employed to compare the ancient samples with those that were prepared potentiostatically. Poorly crystallized tin oxide (SnO2) was found in the α - replacement products of both sample types. The corrosion-resistance of the potentiostatically-treated bronze samples was tested by atmospheric exposure. Comparison with exposed, untreated samples indicated that the treatment was protective.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 432: Symposium S – Aqueous Chemistry and Geochemistry of Oxides , 1996 , 283
Copyright
Copyright © Materials Research Society 1997

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