STRUCTURE OF DENTAL GALLIUM ALLOYS

The interest in gallium alloys as a replacement for amalgam has increa sed in recent years due to the risk of environmental pollution from am algam. Alloy powders with compositions close to those for alloys of am algam are mixed with a liquid gallium alloy. The mix is condensed into a prepared cavity in much the same way as for amalgam. The aim of the present work was to study the structure of: (1) two commercial alloy powders containing mainly silver, tin and copper, and (2) the phases f ormed by mixing these powders with a liquid alloy of gallium, indium a nd tin. One of the alloy powders contained 9 wt% palladium. Cross-sect ions of cylindrical specimens made by these gallium mixes were investi gated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Discrete grains of the following phases were fo und to be present in both gallium alloys: hexagonal Ag2Ga, tetragonal Cu(Pd)Ga-2, cubic AggIn4 and tetragonal beta-Sn. Indications of hexago nal or orthorhombic Ag2Sn were found in the remaining, unreacted alloy particles. In the palladium-containing alloy the X-ray reflections in dicate a minor fraction of cubic CugGa4 in addition to the Cu(Pd)Gap p hase. Particles of beta-Sn are probably precipitated because Sn-Ga pha ses cannot be formed according to the binary phase diagram. (C) 1996 E lsevier Science Limited