Solvent diffusion in α-silver-tin alloys

Abstract

Coefficients for diffusion of Ag 110m in α- Ag-Sn alloys were measured as a function of temperature and concentration over the temperature range 950–1150 K and 0 to 9 at.% tin.The standard sectioning technique and the method developed by Kriukov and Shukovitzky were applied. The latter involves less experimental effort and, as for relative measurements, even proved to be the more accurate. A strong non-linear increase in the solvent diffusion upon alloying was observed in agreement with results on similar alloys, such as Ag-Cd, Ag-In and Ag-Sb. This is very much in contrast to recent data on solvent diffusion in Ag-Sn, published by Gas and Bernardini, who found a linear enhancement up to 6 at.% tin. The marked dependence of solvent diffusion on temperature and impurity concentration is discussed in terms of the complex model proposed by Hehenkamp, Schielt and Sander to describe the solvent and solute diffusion beyond the limit of infinite dilution. Changes in the solvent correlation factor upon alloying are taken into account by introducing effective jump frequencies. It is shown, how the experimentally observed proportionality of the normalized solvent diffusion coefficient to the normalized vacancy concentration serves to get useful information about the diffusion behaviour such as the linear enhancement factor, average effective jump frequencies, activation energies and free binding enthalpies of impurity-vacancy-associates. According to Lidiard the impurity correlation factor in the case of infinite dilution is calculated, combining the linear enhancement factor with data on solute diffusion. The results are in good agreement with values from measurements of the isotope effect.