Evaluation of the amalgamation reaction of experimental Ag-Sn-Cu alloys containing Pd using a mercury plating technique

A mercury plating technique was used to determine the phases forming on experimental Ag-Sn-Cu alloy powders (with and without Pd) exposed to electrolytically deposited mercury. Four series of alloy powders were made: a) 1.5% Pd with 10-14% Cu (CU series); b) 1.0% Pd with 10-14% Cu (1PD series); c) 1.5% Pd with different ratios of Ag₃Sn (γ) to Ag₄Sn (β) with 12% Cu (AGSN series); and d) 9-13% Cu with no Pd (NOPD series). Each powder was pressed on a freshly prepared amalgam specimen made from the same powder and metallographically polished until cross sections appeared; mercury was electroplated on the alloy particles. Alloy powders, amalgams and electroplated specimens were examined using XRD and SEM/EDS. XRD confirmed the presence of γ₂ in amalgams made from alloys with Cu < 13% or with Ag₃Sn/Ag₄Sn > 0.8. Specimens with moderately plated Hg showed γ₁ (Ag₂Hg₃) polyhedra and η′ Cu₆Sn₅, but not γ₂. This method effectively identifies alloys prone to forming γ₂.