Heterogeneous phase equilibria

Minimization of Gibbs energy and heterogeneous phase equilibria... 

Let us now include an additional component to the Fe-0 system considered above, for instance S, which is of relevance for oxidation of FeS and for hot corrosion of Fe. In the Fe-S-0 system iron sulfides and sulfates must be taken into consideration in addition to the iron oxides and pure iron. The number of components C is now 3 and the Gibbs phase rule reads Ph + F = C + 2 = 5, and we may have a maximum of four condensed phases in equilibrium with the gas phase. A two-dimensional illustration of the heterogeneous phase equilibria between the pure condensed phases and the gas phase thus requires that we remove one degree of... 

In the last two sections the formal theory of surface thermodynamics is used to describe material characteristics. The effect of interfaces on some important heterogeneous phase equilibria is summarized in Section 6.2. Here the focus is on the effect of the curvature of the interface. In Section 6.3 adsorption is covered. Physical and chemical adsorption and the effect of interface or surface energies on the segregation of chemical species in the interfacial region are covered. Of special importance again are solid-gas or liquid-gas interfaces and adsorption isotherms, and the thermodynamics of physically adsorbed species is here the main focus. 

The equilibrium conditions for systems with curved interfaces [3] are in part identical to those defined earlier for heterogeneous phase equilibria where surface effects where negligible ... 

Equation (6.27) is the Laplace equation, or Young-Laplace equation, which defines the equilibrium condition for the pressure difference over a curved surface. In Section 6.2 we will examine the consequences of surface or interface curvature for some important heterogeneous phase equilibria. 

Sobocinski, D.P. and F.Kurata. 1959. Heterogeneous phase equilibria of the hydrogen sulfide-carbon dioxide system. AlChE ). 5 545-551. Stouffer, C.E., Kellerman, S.J., Hall, K.R., Holste, J.C., Gammon, B.E., Marsh, K.N. 2001. Densities of carbon dioxide + hydrogen sulfide mixtures from 220 K to 450 K at pressures up to 25 MPa. /. of Chem. Eng. Data 46 1309-18. 

Kohn, J.P. and Kurata, F. 1958. "Heterogeneous Phase Equilibria of the Methane-Hydrogen Sulfide System", AlChE /., 4 211-216. 

As already shown in earlier review papers [2-6,10,12], three different types of heterogeneous phase equilibria are found in fluid mixtures, namely... 

Much more information regarding the construction of ternary and quaternary phase diagrams and also other possibilities of their representation can be obtained from the monographs [1,2]. Also, Refs [3,4] should be recommended as excellent source of fundamental knowledge on heterogeneous phase equilibria. 

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