Main types of fluid phase behavior

Solid circles are the critical points of pure components A and B open triangles are the critical endpoints N (Li = Lj-G) and R (Li = G-L2). Solid lines are the monovariant curves L-G of pure components A and B dashed lines are three-phase equilibrium L1-L2-G dot-dashed lines are the critical curves L = G, originated in the critical points of pure components two-dots-dashed lines are the critical curves Li = L2 originated in critical endpoint N. 

However, the available experimental data show that the above-mentioned seven types of phase diagrams do not describe some versions of fluid phase behavior in the highly asymmetric binary systems where the melting temperature of nonvolatile component is significantly greater than the vapor-liquid critical point of the volatile one. 

---

The classification shown in Figure 1.12 is popular and is convenient to use because it demonstrates not only the main types of fluid phase behavior but also the fluid phase diagrams which appear when the heterogeneous fluid equilibria are bounded not only by another fluid equflibria but also by the equflihria with solid phase that is usually observed in the most real systems. 

The systematic classification in Figure 1.13 consists of four rows (a, b, c, and d) of the diagrams corresponding to the described four main types of fluid phase behavior. 

The complete form of the liquid-liquid immiscibility region can be achieved only if there is no interference of immisci-bihty region and crystallization surface, and this region does not touch the crystallization surfaces but exists only in solid unsaturated solutions (the main types of fluid phase behavior). Types lb, Ic and Id are the versions of complete phase diagrams with three different types of immiscibility region in their complete form. 

The experimental investigations were and are the main sources of information about phase behavior in ternary systems. In the beginning of the twentieth century Smiths (1910, 1913, 1915) using the topological method and available experimental information has considered 12 versions of complete phase diagrams with various types of fluid phase behavior and solid phase transformations. But it was not a systematic classification. 

The following are general regularities for fluid phase behavior in ternary mixtures summarized after the analysis of all main types of fluid phase diagrams ... 

Similarly to the phase diagrams for binary systems, the main types for fluid phase diagrams of ternary mixtures should not have an intersection of critical curves and inunis-cibUity regions with a crystallization surface in them. Combination of four main types of binary fluid phase behavior la, lb, Ic and Id (Figure 1.2) for constituting binary subsystems gives six major classes of ternary fluid mixtures with one volatile component, two binary subsystems (with volatile component) complicated by the immiscibility phenomena and the third binary subsystem (consisted from two nonvolatile components) of type la with a continuous solid solutions. These six classes of ternary fluid mixtures can be referred as ternary class I (with binary subsystems Ib-lb-la), ternary class II (with binary subsystems Ic-lc-la), ternary class III (with binary subsystems Id-ld-la), or ternary class IV (with binary subsystems Ib-ld-la), ternary class V (with binary subsystems Ib-lc-la) and ternary class VI (with binary subsystems Ic-ld-la). 

When molecules in gaseous state adsorb onto the surface of a condensed phase, usually a solid, different behaviors can be observed depending on the adsorbate, the substrate, and the experimental conditions such as temperature. Brunauer et al. (1940) gave a classification with five main fypes which remains in use today, albeit extended with a sixth type (Sing 1985). These types cover the majority of situations, except in some cases supercritical fluids show different behavior (Donohue and Aranovich 1998). Here we discuss the six classical types. 

---