Microprobe Analysis of Amalgam: I. Effect of Surface Preparation

The electron microprobe was used to study the effect of surface preparation on the quantitative analysis of amalgam. Silver-mercury contamination particles were iden-tified. The effect of this contamination could be minimized with careful polishing proce-dures, followed by an immediate analysis in which these particles are avoided. The electron microprobe has been used to analyze the microstructure of dental amal-gam.1-5 The condition of the surfaces of test specimens should be considered, especially if quantitative analysis is to be attempted. Be-cause this instrument has a small diameter electron beam that excites elements primar-ily at the surface of the structure to be an-alyzed, any artifacts on the surface will af-fect X-ray emission. The microstructure of amalgam shows the metallic phases of Ag-Sn (y) and Cu-Sn (Cu3Sn) contained within a matrix of Ag-Hg (yi) and Sn-Hg (y2). Test surfaces that are characteristic of the actual structure in the bulk of the specimen are difficult to prepare because of the different hardnesses of the phases and problems with the phases that contain Hg. Sources of contamina-tion or artifacts may include: (1) bulk transfer of phases caused by differences in hardness; (2) transfer of Hg from the Hg-containing phases caused by surface melting and smearing; and (3) Hg transfer from the Hg-containing phases caused by evap-oration. Several experiments were conducted to examine this problem. The effects of polish-ing procedures, excitation voltages, and Hg vapor on the analysis of the phases of amalgam were determined