Thermodynamics of theβ’-NiZn intermetallic phase exhibiting the CsCl-structure

Abstract

The thermodynamic activity, partial molar entropy and partial molar enthalpy of zinc have been calculated based on the measurement of partial pressure of zinc above eleven β’-NiZn alloys exhibiting the CsCl-type of structure over the temperature interval 1042 to 1159 K, using the dew-point method. Good correlations are found between theory and experiment for all three partial quantities. Furthermore, from these results and the recently reported data on the f.c.c. terminal solid solutions, the corresponding partial quantities of nickel in β’-NiZn alloys are computed as well as the integral quantities. It is found that the thermal entropy of this phase remains constant with composition, an assumption used by Chang and co-workers in deriving the theoretical equations to account for the compositional variations of the thermodynamic properties for this type of ordered phase. A similar analysis is also made for the thermodynamic properties of the low-tempe rature form of the equi-atomic phase exhibiting the face-centered tetragonal superlattice structure.