Microstructures of the set amalgams
Microstructures of the set amalgams of the (A) low-copper, lathe-cut, (B) the high-copper, admix and (C) the high-copper, unicompositional types. These photographs were made by superimposing microprobe X-ray scans of the elements through colored filters; blue for silver, red for copper, and green for tin. The blue/black matrix phase is A2Hg3 (γ1) for all amalgams. The green colored Sn7-8Hg (γ2) phase is only present in the low-copper alloy A. The tangerine colored Cu6Sn5 (η′) phase is minimal in alloy A but substantial in alloys B and C. In alloy B, the source of the increased copper is in the spherical silver-copper eutectic phase where the η′ surrounds this spherical particle. In alloy C, the source of the increased copper is in the additional Cu3Sn added to the spherical Ag3Sn particle and Cu6Sn5 (ηʹ) phases are present around this spherical particle. (Courtesy of Mahler DB, OHSU School of Dentistry, Portland, Oregon.)