Solid solubility of germanium in silver

Abstract

The solid solubility of germanium in silver has been measured in the temperature range of 520K to 913K via measurements of density and of electrical conductivity of two near-eutectic Ag–Ge alloys. The atomic fraction of germanium in solid solution varied between 0.014 and 0.089 over the mentioned range of temperature and an extrapolated maximum solubility of 0.093 at the eutectic temperature of 924K is found. For samples with spheroidized Ge-particles before the equilibrium heat treatments at low temperature for 24 or 48h, thermodynamic equilibrium was supposedly not achieved at temperatures below 723K. Much longer heat treatments (tens of days) on the significantly finer as-cast microstructure allowed to reach equilibrium probably down to 600K. Independently of whether thermodynamic equilibrium was reached or not the electrical conductivity and the density measurements yielded good agreement typically within a few tenth of percent of atomic Ge-concentration in solid solution in α-Ag for a given temperature. The results are close to, yet consistently slightly lower than, the values given by Owen and Rowland on which the current assessment of the solvus in the Ag–Ge binary is based. More recent results by Filipponi and co-workers are clearly not in agreement with the data presented here.