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Title: Electrochemical and electron-microscopical studies of anodically corroded silver-gold alloys
Author: Carter, David A. W.
ISNI:       0000 0001 3522 5283
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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The aims of the project are to investigate the electrochemical parting of silver from silver-gold. Direct measurements by X-ray analysis of corroded specimens show that silver cannot be parted from alloys with initial concentrations of under 55at% silver, it can be incompletely parted from alloys with between 55at% and 80at% silver, and it can be fully parted from alloys which are over 80at% silver. The alloys are used to produce well-defined and characteristic voltammograms, and the lowest potential at which silver can be dissolved from them is shown to be composition-dependent, higher potentials being required to part silver from the less silver-rich alloys. Cyclic voltammograms, together with coulometric measurements, and X-ray analyses of specimen compositions before and after electrochemical treatments provide evidence that the dissolution of silver from these alloys is accompanied by the formation of a new phase, possibly a gold oxide. Since, at the potentials of under 1400mV used for this work, this new phase is not formed on pure gold, it is inferred that the dissolution of silver is associated with the formation a chemical and/or a physical environment in which the new phase can form. This phase has a maximum thickness for alloys with an initial silver concentration of about 64at%. A specialised electrochemical cell, designed and built for this work« is used for the electrochemical treatment of thin, electron-transparent specimens of gold and silver-gold. Following corrosion the specimens are examined with transmission electron microscopy. The development of corrosion micromorphologies is seen not to be strongly composition-dependent, commencing in all silver-rich silver-gold alloys by the formation of isolated pits with diameters of about 50A. After longer periods of corrosion, channels about 50A wide cover the surface of the intragranular regions; when more charge is passed, even these previously apparently uncorroded regions close to grain boundaries and holes through the alloy become covered with networks of channels. The electrochemical observations presented lead to the idea that gold atoms are redistributed from the centres of developing pits and channels by the formation and decomposition of the new phase during the dissolution of silver.
Supervisor: Not available Sponsor: Science Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; QD Chemistry ; TS Manufactures