A Thermodynamic Framework Bridging the Composition and Temperature Dependence of Bulk Modulus With Enthalpy of Mixing

Abstract

The intrinsic thermodynamic links that exist between thermochemical and thermophysical quantities, especially their temperature, pressure, and composition dependence, have seldom been analyzed in sufficient detail in literature. In this connection, an attempt is made to establish a thermodynamic bridge, relating Δo H mix, the standard enthalpy of mixing with Δo B T , the change in isothermal bulk modulus as a result of alloying and its composition and temperature dependence. In essence, by adopting the standard regular and subregular solution approximations to the composition dependence of mixing enthalpy; and furthermore, incorporating separately the configurational (Δo S conf) and vibrational (Δo S Vib) entropy contributions to mixing Gibbs energy change (Δo G mix), simple models have been derived for the composition and temperature variations of excess bulk modulus ΔB T . In particular, a regular or subregular solution analog of the composition variation of ΔB T is shown to be possible if Δo H mix could be described likewise. The vibrational entropy contribution to ΔB T is found to be important only when the change in Gruneisen parameter during alloying turns to be significant. The practical utility of the theoretical framework developed in this study has been demonstrated by applying it to disordered fcc Cu1−x Ni x alloys, wherein it is shown that Δo H mix and Δo B T are linearly correlated, as predicted by the theory.