Journal of Dental Research, Vol 55, 1012-1022, Copyright © 1976 by International & American Associations for Dental Research Online Journals
Microprobe analysis of a Au-containing alloy and its amalgam
D. B. Mahler, J. D. Adey and J. van Eysden
Under near-equilibrium conditions, an alloy ingot containing approximately
64% Ag, 26% Sn, and 10% Au was found by X-ray diffraction to consist of
large grains demonstrating the gamma (Ag-Sn) structure. Microprobe analysis
of these grains showed a 64.2% Ag, 25.3% Sn, and 10.5% Au composition with
very small amounts of AuSn2 and AuSn4 segregated at the grain boundaries.
When this alloy is manufactured in the form of rapidly colled spherical
particles, X-ray diffraction shows both beta (Ag-Sn) and gamma (Ag-Sn)
structures with Au substituting for Ag, and microprobe analysis
demonstrates a segregation of small high Sn, high Au areas having a AuSn2
composition. When Hg is mixed with these spherical particles, gamma1, some
gamma2, and Sn-Au phases (AuSn2 and AuSn4) form. The Au that combines with
Sn seems to come from the beta or gamma phases rather than from the Sn-Au
segregations in the alloy. The small amount of the gamma2 phase that is
initially formed apparently disappears after a short period of time
although there is some question as to whether a very small amount may still
remain. The Ag-Hg hase (gamma1) is essentially the same as found in
conventional amalgams as is the small amount of gamma2 initially formed.
Furthermore, a nonequilibrium state seems to be necessary for the early and
possibly complete elimination of gamma2. In the as-cast condition, after a
period of time at 37 C, A Ag-Hg-Sn phase (beta1) is formed that is similar
to that found in conventional amalgams that serve as restorations in the
mouth for a period of time. However, in the 135-annealed amalgam, no beta1
appears.
