The modified quasichemical model I—Binary solutions

Abstract

Further improvements to the modified quasichemical model in the pair approximation for short-range ordering in liquid and solid solutions are presented. The energy of pair formation is expanded in terms of the pair fractions rather than the component fractions, and coordination numbers are permitted to vary with composition. A formalism is introduced whereby the quasichemical equations are shown to be equivalent to the equations of an associate model if the pairs are formally treated as fractional associates. The model is applied to the liquid phase in a new optimization of the KCl-MgCl 2 system.

Thermodynamic Assessment of the Al-Mn and Mg-Al-Mn Systems

“…The MQM in the pair approximation [8] was used to model the liquid Al-Mn alloys. The liquid phases in the Mg-Al and Mg-Mn sub-systems of the Mg-Al-Mn system were also modeled previously with the MQM.…”

“…[9,10] This model, which takes SRO into account, has been used extensively for molten salts, [11][12][13] slags [14] and sulfides. [15][16][17] All details of the model and notation have been described previously [8] and only a brief summary is given here.…”

“…where g A and g B are the molar Gibbs energies of the pure components, and DS config is the configurational entropy of mixing given by randomly distributing the (A -A), (B -B) and (A -B) pairs in the one-dimensional Ising approximation: [8] …”

“…The composition of maximum SRO is determined by the ratio of the coordination numbers Z B /Z A , as given by the following equations: [8] 1 are defined similarly. (Note that Z A AB and Z A BA represent the same quantity and can be used interchangeably.)…”

“…From the MQM model parameters for the binary liquid phases, the thermodynamic properties of a ternary liquid phase may be estimated as discussed previously. [18] If ternary experimental data are available, additional ternary model parameters may be added if required.…”