Quasichemical solution model

A more accurate type of quasi-chemical solution model was introduced by Guggenheim [E. A. Guggenheim, Mixtures (Oxford University Press, New York, 1952)] to account for specific A + B AB association corrections in both Hfs (x) and st(x). The quasi-chemical approach employs an explicit pair partition function for the equilibrium population of A B complexes in solution. More general associated solution models were also developed to incorporate AB complexes of other than 1 1 stoichiometry [A. D. Pelton and M. Blander. Metall. Trans. 17B, 805-15 (1986)]. Although such quasichemical and solution models can be more accurate, they are also more difficult to implement. 

Note.- We have seen that relation [2.70] of the strictly-iegular solution model was called the Bragg and Williams zero-order approximation. Similarly, in view of relation [2.89], the quasichemical solution is called an approximation of order 1. The order at hand is, in fact, the power to which the exponential appearing in relation [2.89] is raised power zero for the Bragg and Williams model, and power 1 for the quasi-chemical model. 

A useful tool for the development of physically motivated approximate models of solution thermodynamics, particularly in view of quasichemical extensions... 

Pratt and co-workers have proposed a quasichemical theory [118-122] in which the solvent is partitioned into inner-shell and outer-shell domains with the outer shell treated by a continuum electrostatic method. The cluster-continuum model, mixed discrete-continuum models, and the quasichemical theory are essentially three different names for the same approach to the problem [123], The quasichemical theory, the cluster-continuum model, other mixed discrete-continuum approaches, and the use of geometry-dependent atomic surface tensions provide different ways to account for the fact that the solvent does not retain its bulk properties right up to the solute-solvent boundary. Experience has shown that deviations from bulk behavior are mainly localized in the first solvation shell. Although these first-solvation-shell effects are sometimes classified into cavitation energy, dispersion, hydrophobic effects, hydrogen bonding, repulsion, and so forth, they clearly must also include the fact that the local dielectric constant (to the extent that such a quantity may even be defined) of the solvent is different near the solute than in the bulk (or near a different kind of solute or near a different part of the same solute). Furthermore... 

After the seminal work of Guggenheim on the quasichemical approximation of the lattice statistical-mechanical theory[l], various practical thermodynamic models such as excess Gibbs energies[2-3] and equations of state[4-5] were proposed. However, the quasichemical approximation of the Guggenheim combinatory yields exact solution only for pure fluid systems. Therefore one has to resort to numerical procedures to find the solution that is analytically applicable to real mixtures. Thus, in this study we present a new unified group contribution equation of state[GC-EOS] which is applicable for both pure or mixed state fluids with emphasis on the high pressure systems[6,7]. 

A number of directions can be taken to generalize these distributions systematically. Multigaussian models are natural possibilities, and suggest the quasichemical theory taken up later. Here we assume that the distribution P (e i ") in Eq. (4.19) can be expressed as a linear combination of gaussians corresponding to configurational substates of the system. As an example for aqueous solutions, the... 

The equilibrium and dynamics of adsorption processes from micellar surfactant solutions are considered in Chapter 5. Different approaches (quasichemical and pseudophase) used to describe the micelle formation in equilibrium conditions are analysed. From this analysis relations are derived for the description of the micelle characteristics and equilibrium surface and interfacial tension of micellar solutions. Large attention is paid to the complicated problem, the micellation in surfactant mixtures. It is shown that in the transcritical concentration region the behaviour of surface tension can be quite diverse. The adsorption process in micellar systems is accompanied by the dissolution or formation of micelles. Therefore the kinetics of micelle formation and dissociation is analysed in detail. The considered models assume a fast process of monomer exchange and a slow variation of the micelle size. Examples of experimental dynamic surface tension and interface elasticity studies of micellar solutions are presented. It is shown that from these results one can conclude about the kinetics of dissociation of micelles. The problems and goals of capillary wave spectroscopy of micellar solutions are extensively discussed. This method is very efficient in the analysis of micellar systems, because the characteristic micellisation frequency is quite close to the frequency of capillary waves. 

The thermodynamic properties of the liquid Co-Fe-S solutions were predicted using the modified quasichemical model for short-range ordering by [1999Kon] and very good agreement with experimental data was obtained. 

The idea of treating in one dimension a system which has proved intractable in three is of course not new, and a number of authors have treated one-dimensional solutions. The results have proved to be semi-quantitatively applicable to the corresponding three-dimensional situation, and constitute the justification of the so-called quasichemical approximation. In view of this it might be hoped that the one-dimensional plasma would also serve as a model for the actual three-dimensional system, but it will appear that the equations of state for the two cases are quite different. 

The solution thus modeled is called Fowler and Guggenheim s quasichemical model. 

The Modified Quasi-chemical Model [10,11] has been applied successfully to slag solutions. However, for a solution where substitution is possible on two sublattices ([Ca, Fe ][0, F] in the present case) the quadnqrlet approximation should be used [12]. The two most important quasichemical reactions between quadruplets can be represented as follows ... 

A. D. Pelton, S. A. Degterov, G. Eriksson, C. Robelin, and Y. Dessureault, "The modified quasichemical model I - Binary solutions," Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science, 31(4) (2000), 651-59. 

We tiy to model the high-temperature phase of T alumina as a solid solution of substitution, hydroxide ions being substituted by oxygen ions. Express the quasichemical reaction of water departure. Consider that the model led to a concentration... 

Ale] Calculation Application of quasichemical model predict activity of C in solid solutions... 

---