Dental gallium alloy composites studied by SEM and TEM.

Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag-Sn-Cu rich alloy powder) and a GF powder (Ag-Sn-Cu-Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag-based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X-ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high-resolution electron microscopy and energy-dispersive X-ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag3Sn, cubic Ag9In4, tetragonal beta-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions were observed consisting of an intergrowth of tetragonal CuGa2 and one of the cubic gamma-Cu9Ga4 phases. In addition to these phases cubic Ga7Pd3 was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga7Pd3.