THERMODYNAMIC PROPERTIES OF THE PHASES-ZETA AND AUSN IN THE SYSTEM AU-SN

Metal solution calorimetry has been used to measure the low temperature heats of formation and heat contents of two phases in the system Au-Sn. The heats of formation of zeta containing 11.1, 14.0 and 16.0 at. pct Sn and AuSn at 78 K and of zeta containing 16.0 at. pct Sn and AuSn at 195 and 273 K have been measured. The heat contents (H 273K-H 78K) and (H 195K-H 78K) of zeta (16· at · pct Sn)and AuSn have also been measured. Heat contents at several temperatures and the standard heat and free energy of formation of AuSn at 298 K have been calculated. The stability of zeta and the unusual composition dependence of its heat of formation have been discussed in terms of its electronic structure. © 1979 American Society for Metals and the Metallurgical Society of AIME.