Measurement of solid solubility of germanium in aluminum

The solid solubility of Ge in aluminum was determined by resistivity measurement at 77 K of Al-Ge alloys annealed at various temperatures for times sufficient to complete the precipitation of the equilibrium Ge phase. The solid solubility of Ge in aluminum was found to vary from 0.252 at. pct at 533 K to 1.82 at. pct at 693 K. From the temperature dependence of the solid solubilities, the excess entropy of mixing ΔS and heat of mixing ΔH associated with the formation of solid solution of Ge in aluminum were calculated to be 2.77 R and 38.5 kJ mol^-1, respectively. Using these values of ΔS and ΔH, the maximum solid solubility of Ge in aluminum was calculated to be 2.08 at. pct at the eutectic temperature 697 K. The magnitude Δρ _Ge ⁷⁷ /Δc due to 1 at. pct impurity was determined to be 8.60 nΩm/at. pct Ge. The resistivity of Al-1.32 at. pct Ge alloys aged at 573 and 623 K was measured at 77 K to determine the time variation of the average concentrationc of the solute in the matrix during coarsening of the Ge precipitates. The value ofc, calculated using the value of Δρ _Ge ⁷⁷ /Δc, decreased linearly in accordance with the t^-1/3 law. The concentration of the solute in the matrix, in equilibrium with the Ge particle of infinite size, was determined by extrapolating thec vs t^-1/3 plot to infinite time, in excellent agreement with the above solid solubility. Formerly Graduate Student, Department of Materials Science, Tohoku University