Phase diagrams classification

Data for the hydrogen sulfide-water and the methane-n-hexane binary systems were considered. The first is a type III system in the binary phase diagram classification scheme of van Konynenburg and Scott. Experimental data from Selleck et al. (1952) were used. Carroll and Mather (1989a b) presented a new interpretation of these data and also new three phase data. In this work, only those VLE data from Selleck et al. (1952) that are consistent with the new data were used. Data for the methane-n-hexane system are available from Poston and McKetta (1966) and Lin et al. (1977). This is a type V system. 

Partial pressure as a variable. As mentioned in 2.1, many types of thermodynamic variables may be used in the construction of phase diagrams. The various rules of construction, based on the laws of chemical thermodynamics, which apply to the different types of phase diagrams have been discussed in several books and papers (for instance, Pelton and Schmalzried 1973, Okamoto 1991, Pelton 1991). Following a classification proposed by Pelton, the various, bidimensional, phase diagrams may be subdivided into three types as follows ... 

Considering now a few common methods and techniques for the experimental definition of a phase diagram, it may be useful to refer to their usual classification into two groups polythermal and isothermal methods. 

The mysteries of the helium phase diagram further deepen at the strange A-line that divides the two liquid phases. In certain respects, this coexistence curve (dashed line) exhibits characteristics of a line of critical points, with divergences of heat capacity and other properties that are normally associated with critical-point limits (so-called second-order transitions, in Ehrenfest s classification). Sidebar 7.5 explains some aspects of the Ehrenfest classification of phase transitions and the distinctive features of A-transitions (such as the characteristic lambda-shaped heat-capacity curve that gives the transition its name) that defy classification as either first-order or second-order. Such anomalies suggest that microscopic understanding of phase behavior remains woefully incomplete, even for the simplest imaginable atomic components. 

In this section we will discuss the phase behaviour of binary systems. In 2.2.2.1 the classification of fluid phase behaviour according to van Konynenburg and Scott [5] is discussed. The occurrence of solid phases introduces an extra complication in binary phase phase diagrams. This is discussed in 2.2.2.2. 

Figure 14.10 The five types of (fluid + fluid) phase diagrams according to the Scott and van Konynenburg classification. The circles represent the critical points of pure components, while the triangles represent an upper critical solution temperature (u) or a lower critical solution temperature (1). The solid lines represent the (vapor + liquid) equilibrium lines for the pure substances. The dashed lines represent different types of critical loci. (l) [Ar + CH4], (2) [C02 + N20], (3) [C3H8 + H2S],...

A number of additional DTA experiments were undertaken with various compositions within the binary system up to 66.6 at. % S (= MoS2 composition). In Fig. 7 a phase diagram is shown in which all results are incorporated. With respect to the above-mentioned classification of sulfide systems14), the Mo—S system, as well as the Cr—S system, exhibits Type 1 two regions of immiscible liquids one field of liquid immiscibility in the metal-rich portion at high temperatures, and a second two-liquid field in the sulfur-rich region beyond MoS2 which is not shown in Fig. 7. 

The systematic investigation of order phase diagrams, such as that shown in Fig. 9 but for different molecular interactions, the location of inherent structures in the order plane, and the comparative exploration of order (or disorder) in computer glasses generated by different quenching protocols are, we beheve, fruitful avenues for research into the nature, classification, and quantification of disorder in glasses and other technologically important nonequilibrium materials. 

Figure 8. P-T projections of main phase diagram types. The roman numbers correspond to the classification introduced by Scott and van Konynenburg the solid lines are critical curves the dashed lines are vapor pressure curves of pure components with critical points Ci and the dash dotted lines are three phase lineg C is critical end point.

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