The thermodynamic properties of liquid Ag−Si alloys

Abstract

The vapor transportation method was used to determine the partial pressure of silver above molten Ag−Si solutions in the temperature range of 1450° to 1600°C. With the use of previously determined values for the partial pressure of liquid pure silver, values for the activity of silver were calculated and fitted to the orthogonal polynomial “Z-series” recently developed by Williams to represent the thermodynamic behavior of binary solutions. The silicon properties were determined analytically using the Gibbs-Duhem equation and the coefficients obtained from the silver data. Silver was found to exhibit positive deviations from ideality in alloys containing less than about 50 at. pct Ag. In the silver-rich solutions, silver showed negative deviations from Raoult's law. However, at 1550° and 1600°C, the negative silver departures were quite small. Within the limit of experimental error, silicon showed positive deviations from ideality at all temperatures studied for alloys containing more than 10 at. pct Si. At infinite dilution the silicon deviations were quite small. Regular solution behavior cannot describe the thermodynamics of liquid Ag−Si alloys.