The reaction zone around commercially available amalgam alloy particles of Ag-Cu eutectic composition.

An electron microprobe was used to investigate the composition and microstructure of regions in the reaction zones around particles of approximately Ag-Cu eutectic composition in commercially available and experimental dispersion modified amalgams. Two distinct regions were identified. Techniques of phase composition analysis were further developed in order to identify and quantify the component phases present in the two regions. The outer, somewhat clumped region contained principally a network of strands and particles of eta 1 (Cu6Sn5) composition and some gamma 1 phase. After phase composition analysis, the inner region was found to contain eta 1 phase and substantial quantities of gamma 1 phase, a Cu-Hg phase (probably Cu4Hg3 formulation) and unreacted Ag-Cu. The two regions may be best described as eta 1-rich and eta 1-sparse, respectively.