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Lookup NU author(s): Dr Todd Green,
Professor Sudipta Roy
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An analysis of the speciation of gold plating solutions containing sulfite and thiosulfate as complexing agents has been performed. In the case of gold sulfite baths, it was found that the observed stability and electrochemical behavior were inconsistent with the commonly assumed stability constants of Β= 1010 for the Au (S O3) 2 3- species. The data are, however, consistent with a much larger stability constant of Β= 1027. In gold plating baths containing sulfite and thiosulfate ligands, the speciation model predicts that the dominant species at neutral or basic are mixed complexes of the form Au (S2 O3) (S O3) 3- and Au (S2 O3) (S O3) 2 5-. The thiosulfate complex Au (S2 O3) 2 3- is only dominant under acidic conditions. It is shown that the electrodeposition characteristics reported in many studies can be interpreted in terms of the existence of such mixed ligand complexes. Finally, the effect of the stability of various gold plating solutions on colloidal gold formation has been explored. For free-standing solutions, decomposition is more likely to occur via the disproportionation of Au(I) species such as AuOH, Au (OH) 2-, and Au Cl2- rather than free aurous ions. The stability of gold baths during electrodeposition is mainly influenced by the formation of dithionite ions which reduce Au(I) complexes to form colloidal gold. © 2006 The Electrochemical Society. All rights reserved.
Author(s): Green TA, Roy S
Publication type: Article
Publication status: Published
Journal: Journal of the Electrochemical Society
ISSN (print): 0013-4651
ISSN (electronic): 1945-7111
Publisher: Electrochemical Society, Inc.
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