Journal of Dental Research, Vol 63, 1014-1018, Copyright © 1984 by International & American Associations for Dental Research Online Journals
Tarnish and corrosion of a commercial dental Ag-Pd-Cu-Au casting alloy
L. Niemi and R. I. Holland
The correlation between microstructure, tarnish, and corrosion behavior of
a commercial dental Ag-Pd-Cu-Au casting alloy after various heat treatments
was studied. The attacked structural components were identified by
comparing SEM micrographs with light optical micrographs taken after
exposure of the alloy to a 2% Na2S solution and after dynamic polarization
in de-aerated artificial saliva. The characteristic dynamic polarization
curves for the alloy after the heat treatments were established. The
results were verified by analogous testing of two experimental alloys with
compositions similar to those of the analyzed components in the commercial
alloy annealed at 600 degrees C for seven wk. The matrix of the commercial
alloy was decomposed, according to the heat treatments, into varying
proportions of a tarnish- and corrosion-resistant Cu- and Pd-rich component
(A) and a nonresistant Ag-rich component (B). The presence of A
considerably increased the tarnish rate of B, due to galvanic coupling.
Age-hardening of the alloy increased the proportion of the tarnish- and
corrosion-prone component B.
