Solutions strictly regular solution

This is a model of a strictly regular solution as used by R. Fowler and E. A. Guggenheim, Statistical Thermodynamics, Cambridge University Press, New York, 1949. 

As an example of the application of the above formulae let us examine the behaviour of a strictly regular solution. In a ternary regular solution we have... 

These examples show the generality of these qualitative rules which were in fact only derived above for strictly regular solutions.f... 

Equation (6.27) is frequently used in the calculation of surface adsorption in dilute solutions. For strictly regular solutions, the activity coefficient is defined as... 

Such a transfer to the model of strictly regular solutions can be made by giving the quantity Ae in Equation 28 the meaning of an additional increment of the Gibbs potential... 

Therefore, transfer to the model of strictly regular solutions leads to the addition of the second summand to the expression for x comparison with Equation 33... 

The expressions of the Gibbs potential of mixing, like Equations 31 and 32 with x comprising two summands, Xs + Xh derived immediately within the framework of the methodology of strictly regular solutions, see Equations 4.65 and 4.80 in (Tompa, 1956). In the zero approximation... 

A model for the strictly regular solution ASmix.uncomt 0) requires x = X, =... 

Hildebrand [19] used this term to suggest that these are mixtures whose behaviour is regular as revealed by experiment Guggenheim [20] added the concept of a strictly regular solution. The strictly regular... 

Fig. 1.2 Solvus (solid line) and spinodal (dashed) for a strictly regular solution (Wg = 0), assuming Wh to be constant. Phases within the spinodal are unstable with respect to internal diffusion...

By choosing the model of a strictly-regular solution for the solid solution, we obtain the results shown in Figure 3.1, where we show the hydrogen pressure at equilibrium as a function of its atomic fraction in the solid. Note that we have a very good coincidence between the curves given by the model and the experimental points. These results are as satisfeetory for zones with a... 

Figure 13.4 The phase diagram for strictly regular solutions...

Essentially, we are looking at the solubility of metals in other metals - i.e. monophase metal alloys. The most commonly used solution models are the models with similar atomic volumes, which give us the perfect solution, the infinitely-dilute solution and the strictly-regular solution. Thus, we will then look at Guggenheim s quasi-chemical model, which includes the notion of short-distance order. 

Thus, the difference between the strictly-regular solution and the perfect solution is simply the exchange energy, which is null for the latter. ... 

Let us look again at the above model of the strictly-regular solution (section 2.3.3). If the number of molecules in B is smaller than that of A - i.e. if the solution is very dilute in terms of B - then relation [2.72] gives us ... 

Thus, the ideal dilute solution is a specific case of the strictly-regular solution when one of the components is present only in very small proportions. 

We have just examined three models of solutions. The most commonly found is that of the strictly-regular solution. The other two models are two specific cases that of the perfect solution if we make... 

Figure 2.11 shows the gap between the excess Gibbs molar energy of the strictly-regular solution and that of this model, for the values T = 800 K, z = 12 and NaWAB = 30 kJ. The two curves exhibit a minimum at Xa = Xb = 0.5. 

In order to evaluate the functions g(5) and E s), we need to know the distribution of the atoms on the lattice for the given value of s. Two models have been developed the Gorsky, Bragg and Williams model and the quasi-chemical model. The hypotheses upon which these models are based are similar, respectively, to those used for the model of a strictly-regular solution (see section 2.3.3) and those used for Fowler and Guggenheim s quasi-chemical solution model (see section 2.3.5). 

A group of solutions known as strictly-regular solutions is of significant interest for a number of reasons ... 

As strictly-regular solutions are, by definition, regular, we can deduce that the entropy of mixing is the same as that of a perfect solution and therefore that the excess entropy is null. 

We shall now calculate the other main thermodynamics involved in strictly-regular solutions. 

As the enthalpy of mixing for a perfect solution is zero, the enthalpy of mixing for a strictly-regular solution is identical to its excess enthalpy, so for the the partial molar values ... 

As we saw earlier, because a strictly-regular solution is a regular solution, it obey s Kopp s law of additivity (see relation A.2.14 in Table A.2.1, Appendix 1) for the molar heat capacities. 

Figure 2.2. Activity (in convention I) of a component of a strictly regular solution as as a function of the composition...

Figure 2.3 illustrates the activity of a strictly-regular solution as a function of the composition. We can see that the solution displays positive deviation in relation to Raoult s law if B/T < 0, and negative deviation if B/T > 0. If B/T is greater than 2, the inflection point indicates demixing into two solutions, whose compositions are given by the endpoints of the plateau. The activities on either side of the plateau correspond to a metastable phase. 

Note 2.2.- the strictly-regular solution becomes a perfect solution if the parameter 5 is 0 for all compositions B/T = 0). The corresponding curve in... 

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