and spherical particles of different or the same composition (admixed). The properties of set amalgam depends upon the alloy composition—particle size, shape and distribution—and heat treatment controls the characteristic properties of the amalgam. Low copper alloy During trituration, mercury diffuses into the silver-tin particles. Then, silver and tin dissolve, to a very limited extent, into the mercury. As this occurs, the particles become smaller. Because the solubility of both silver and tin in mercury is limited and because silver is much less soluble in mercury than is tin, silver precipitates out first as silver-mercury (γ1) followed by tin in the form of tin-mercury (γ2). The set amalgam consists of unreacted gamma particles surrounded by a matrix of gamma 1 and gamma 2. The amalgamation is summarised as follows: Ag3Sn, Ag5Sn + Hg → Ag2Hg3 + Sn8Hg + Ag3Sn i.e. (γ + β) + Hg → γ1 + γ2 + γ High copper alloy In high copper alloy, copper is added to improve mechanical properties, resistance to corrosion and marginal integrity. The higher copper is supplied by either the silver-copper eutectic or the Cu3Sn (ε) phase. The fact that tin had a greater affinity for copper than for mercury meant that the gamma-2 phase was reduced or eliminated. This resulted in the dramatic improvement in physical properties. The higher copper content is supplied as two types: High copper admix alloy (spherical particles of the silver-copper eutectic alloy to a low-copper lathe-cut alloy in a ratio of 1:2) Uni/single-composition alloy Admix alloy setting reaction During trituration, the dissolved silver from the silver-tin particles reacts, as in low copper alloys, to form the γ1 phase. The dissolved tin migrates to the outside of the silver-copper particles to form Cu6Sn5, the eta prime (η′) phase of the copper-tin system. Thus, copper reacts with sufficient tin to prevent the formation of γ2. The amalgamation reaction may be simplified as follows (notice the absence of γ2 phase): γ(Ag3Sn) + Ag-Cu (eutectic) + Hg → γ1 (Ag2Hg3)+ η ′ (Cu6Sn5)+ unreacted γ (Ag3Sn) + unreacted Ag-Cu (eutectic) Uni/single composition alloy Here, the alloy particles contain both Ag3Sn(γ) and Cu3Sn(ε), similar to the low-copper lathe-cut alloys, but with much greater amount of the Cu3Sn(ε) phase. These alloys are usually spherical. When liquid mercury is mixed with these alloys, it diffuses into the surface of these particles forming Ag2Hg3 as well as Cu6Sn5. γ(Ag3Sn) + ɛ(Cu3Sn) + Hg →