Generalized binary phase

Phase diagrams are the roadmaps from which the number of phases, their compositions, and their fractions can determined as a function of temperature. In general, binary-phase diagrams can be characterized as exhibiting complete or partial solid solubility between the end members. In case of the latter, they will contain one or both of the following reactions depending on the species present. The first is the eutectic reaction is which a liquid becomes saturated with respect to the end members such that at the eutectic temperature two solids precipitate out of the liquid simultaneously. The second reaction is known as the peritectic reaction in which a solid dissociates into a liquid and a second solid of a different composition at the peritectic temperature. The eutectic and peritectic transformations also have their solid state analogues, which are called eutectoid and peritectoid reactions, respectively. 

Fig. 38. Isothermal sections at 25°C of (a) intra-lanthanide and (b) intra-actinide generalized binary phase diagrams, showing equilibrium phase boundaries [with estimated hysteresis for (a)] as full hnes (Benedict et al. 1986). The broken line in (a) indicates the interpolated boundary for the volume collapse transition of the lanthanides. The atomic radius of Ce at room temperature as a function of pressure is shown in (c) (Franceschi and Olcese 1969), with the Kondo-volume collapse transition at about 7 kbar. This transition can be traced to negative pressures by alloying (Lawrence et al. 1984), as seen in (d) via the temperature dependence of the resistance.

W. G. Moffat, Handbook of Binary Phase Diagrams, General Electric Co., Schenectady, N.Y., 1976. 

The general thermodynamic treatment of binary systems which involve the incorporation of an electroactive species into a solid alloy electrode under the assumption of complete equilibrium was presented by Weppner and Huggins [19-21], Under these conditions the Gibbs Phase Rule specifies that the electrochemical potential varies with composition in the single-phase regions of a binary phase diagram, and is composition-independent in two-phase regions if the temperature and total pressure are kept constant. 

The binary compounds of palladium and platinum show a higher diversity of structures than found for the Rh-Ir and Ru-Os systems. Aside from several other reported binary phases, four general families can be distinguished ... 

Thermodynamic models are widely used for the calculation of equilibrium and thermophysical properties of fluid mixtures. Two types of such models will be examined cubic equations of state and activity coefficient models. In this chapter cubic equations of state models are used. Volumetric equations of state (EoS) are employed for the calculation of fluid phase equilibrium and thermophysical properties required in the design of processes involving non-ideal fluid mixtures in the oil and gas and chemical industries. It is well known that the introduction of empirical parameters in equation of state mixing rules enhances the ability of a given EoS as a tool for process design although the number of interaction parameters should be as small as possible. In general, the phase equilibrium calculations with an EoS are very sensitive to the values of the binary interaction parameters. 

Figure 2.13. Building blocks of binary phase diagrams examples of three-phase (invariant) reactions. In the upper part the general appearance, inside a phase diagram, of the two types of invariant equilibria is presented, that is, the so-called 1 st class (or eutectic type) and the 2nd class (or peritectic type) equilibria. In the lower part the various invariant equilibria formed by selected binary alloys for well-defined values of temperature and composition are listed. In the Hf-Ru diagram, for instance, three 1 st class equilibria may be observed, 1 (pHf) — (aHf) + HfRu (eutectoid, three solid phases involved), 2 L — (3Hf + HfRu (eutectic), 3 L —> HfRu + (Ru) (eutectic).

In the previous chapter we looked at some questions concerning solid intermetallic phases both terminal (that is solubility fields which include one of the components) and intermediate. Particularly we have seen, in several alloy systems, the formation in the solid state of intermetallic compounds or, more generally, intermetallic phases. A few general and introductory remarks about these phases have been presented by means of Figs. 2.2-2.4, in which structural schemes of ordered and disordered phases have been suggested. On the other hand we have seen that in binary (and multi-component) metal systems, several crystalline phases (terminal and intermediate, stable and also metastable) may occur. 

An-An alloys. A summary ofthe phase diagrams for adjacent actinide metals is shown in the connected binary phase diagrams of Fig. 5.11. The structure of this diagram resembles that reported in Fig. 5.10 for the lanthanides notice, however, that such a sequence of interconnected diagrams could be used as a generalized diagram in a more limited way only, possibly for the heavier actinides from americium onward. 

The term surface alloy is somewhat generic and may refer to a variety of different systems. Here, we apply it to those systems where ultra-thin metal layers (i.e. a few atomic layers thick) are deposited on a bulk metal surface and where the system is subsequently annealed in vacuum in order to obtain alloying in a surface region a few atoms thick. In these conditions it is possible to obtain single atomic layer binary phases, or multilayer surface alloy phases (also termed epitaxial alloys (for a general discussion of these surface alloys, see [5]. Relatively to the subject of the present paper, two Pt-Sn systems have been studied Sn-Pt(l 11) and Sn-Pt(lOO). The behavior and the structural properties of these systems will be discussed in detail in the following. 

---