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Abstract
Crystallographic data have been used to calculate the volumes of reactants and products involved in the amalgamation of Ag, Sn, and Ag-Sn alloys. The calculated volumes have been compared with direct volumetric measurements of macroscopic specimens both with and without porosity. When porosity was zero both before and after amalgamation, all of the specimens contracted during setting, in agreement with calculations. Therefore, any specimens showing expansion during setting developed pores during the process.
Ag-Hg products showed little or no ability to move into or form in pores previously occupied by Hg. Therefore, Ag amalgams developed high porosity and showed great macroscopic expansion during setting.
The Sn-Hg product (γ-phase) appeared to have high mobility and filled the pores readily. Therefore, high-Sn amalgams had little porosity and showed zero dimensional change or contraction during setting.
Initial contraction during setting is believed due to Hg moving into microcracks in the alloy particles. The major expansion is due to crystal growth (γ-Ag-Hg) accompanied by an increase in porosity. Long-term contraction is due to the γ1 – β1 phase transformation.