This study provides further information about the thermal behavior of dental amalgams. A differential thermal analyzer with a thermogravimetric analyzer, and a differential scanning calorimeter (DSC) were employed to examine the thermal stability and phase changes of low and high-copper amalgams. The analysis was performed in air over a temperature range of 25-130°C. Within experimental error (TG sensitivity=20 μg), there was no weight change in any of the amalgams tested. It is suggested that a film formed on the amalgam surface that kept mercury release to a minimum. As previously reported, DSC thermograms have indicated the existence of a phase transformation in both low and high-copper amalgams. Near 80°C, the γ1 in low-copper amalgam transformed to a liquid phase as a result of a solid-state reaction between the existing phases. In high-copper amalgam, the phase transformation occurred at a higher temperature, approximately 100°C, due to the reaction between γ1 and γ and the lack of γ2 in the amalgam. In both cases, the γ1 phase transformed to β1 at the endothermic peak. The heat of reaction estimated from integration of the endothermic peak in each DSC thermogram was approximately the activation energy for diffusion of mercury in amalgam phases and the heat of fusion of γ1 and γ2 in the amalgams.
- amalgam, thermal stability, phase change
ASJC Scopus subject areas
- Materials Science(all)
- Mechanics of Materials