Single Solid Phases

Selwood, Proceedings of the 4th International Congress on Catalysis , Moscow, 1968, Akademiai Kiado, Budapest, 1971, Vol. 2, p. 248. 

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Alloys are classified broadly in two categories, single-phase alloys and multiple-phase alloys. A phase is characterized by having a homogeneous composition on a macroscopic scale, a uniform structure, and a distinct interface with any other phase present. The coexistence of ice, liquid water, and water vapor meets the criteria of composition and structure, but distinct boundaries exist between the states, so there are three phases present. When liquid metals are combined, there is usually some limit to the solubility of one metal in another. An exception to this is the liquid mixture of copper and nickel, which forms a solution of any composition between pure copper and pure nickel. The molten metals are completely miscible. When the mixture is cooled, a solid results that has a random distribution of both types of atoms in an fee structure. This single solid phase thus constitutes a solid solution of the two metals, so it meets the criteria for a single-phase alloy. 

S. K. Sarkar, R. S. Garigipati, J. L. Adams and P. A. Keifer, An NMR method to identify nondestructively chemical compounds bound to a single solid-phase-synthesis bead for combinatorial chemistry applications, J. Am. Chem. Soc., 1996, 118, 2305-2306. 

T. Parkas, L Loo, J. Teuscher, and K. Kallury, "Rapid and Reproducible Extraction of Acrylamide in French Fries Using a Single Solid-Phase Sorbent," Am. Lab. New Ed. October 2003, p. 10.]... 

EUTECTOID. This is a phase transformation analogous to an eutectic where n single solid phase, instead of a liquid phase, is transformed into two or more different solid phases. The number of solid phases in the... 

It might occur that CaO and CaC03 form a solid solution or a mixture in which the particles are so small that it is preferred to consider them as constituting a single solid phase. The system then has two phases and two degrees of freedom. The additional degree of freedom is now the concentration of the solid phase, which is analogous to the relative amounts of the two solid phases when they are considered as separate phases. We are free to set either of these quantities. 

Lacey ME, Sweedler JV, Larive CK, Pipe AJ, Farrant RD, 1H NMR Characterization of the product from single solid-phase resin beads using capillary NMR flow probes, J. Magn. Reson., 153 215-222, 2001. 

Sarkar S, Garigipati RS, Adams JL, Keifer PA, An NMR method to identify nondestructively chemical compounds bound to a single solid-phase-synthesis... 

At the cryohydric point, therefore, we are not dealing with a single solid phase, but with two solid phases, ice and salt and, as we have already learned, the constancy of temperature and composition at the cryohydric or eutectic point is due to the fact that we are dealing with an invariant system. 

Solubility Curves at the Transition Point.—At the transition point, as has already been shown, the double salt and the two constituent salts can exist in equilibrium with the same solution. The transition point, therefore, must be the point of intersection of two solubility curves the solubility curve of the double salt and the solubility curve of the mixtures of the two constituent salts. It should be noted here that we are not dealing with the solubility curves of the single salts separately, for since the systems are composed of three components, a single solid phase can, at a given temperature, be in equilibrium with solutions of different composition, and two solid phases in contact with solution (and vapour) are therefore necessary to give a univariant system. The same applies, of course, to the solubility of the double salt for a double salt also constitutes a single phase, and can therefore exist in equilibrium with solutions of varying composition. If, however, we make the restriction (which we do for the present) that the double salt is not decomposed by water, then the... 

Since the salts were originally present in equimolccular proportions, the final result of evaporation will be the pure double salt. If when the solution has reached the point E the salt A which had separated out is removed, double salt only will be left as solid phase. At a given temperature, however, a single solid phase can exist in equilibrium with solutions of different composition. If, therefore, isothermal evaporation is continued after the removal of the salt A, double salt will be deposited, and the composition of the solution will change in the direction EF. At the point F the salt B will separate out, and on evaporation both double salt and the salt B will be deposited. In the former case (when the salt A disappears on evaporation) we are dealing with an incoftgruently saturated solution but in the latter case, where both solid phases continue to be deposited, the solution is said to be congruently saturated -... 

In Fig. 143, it may be mentioned, the curves dg eg and fg represent quaternary solutions in equilibrium with two solid phases, while the areas adgf hdge and cegf represent quaternary solutions in equilibrium with a single solid phase A, B, or C. 

The different areas, adkh, bdke, etc., of the projection figure represent the composition of solutions with which the single solid phases FeSO. 7H2O, Li2S04. HgO, etc., can exist. Since the curves separating two areas represent solutions in equilibrium with the two solid... 

Ternary Systems.—Wq pass over the binary system FeClg—HgO, which has already been discussed (p. 187), and the similar system HCl—HgO (see Fig. 132), and turn to the discussion of some of the ternary systems represented by points on the surface of the model between the planes XOT and YOT. As in the case of carnallite, a plane represents the conditions of concentration of solution and temperature under which a ternary solution can be in equilibrium with a single solid phase (bivariant systems), a line represents the conditions for the co-existence of a solution with two solid phases (univariant systems), and a point the conditions for equilibrium with three solid phases (invariant systems). 

A more detailed representation of phase equilibrium in a pure fluid, including the presence of a single solid phase, js given in the three-dimensional PVT phase diagram of Fig. 7.3-5. Such complete phase diagrams are rarely available, although data may be available in the form of Fig. 7.3-4, which is a projection of the more complete diagram onto the P-V plane, and Fig. 7.3-6, which is the projection onto the P-T plane. 

Figure 7.3-5 The PVT phase diagram for a substance with a single solid phase. [Adapted from J. Kestin, A Course in Thermodynamics, vol. I. 1966 by Blaisdell Publishing Co. (John Wiley Sons, Inc.) Used with permission of John Wiley Sons, Inc.]...

We start with Eq. 7.4-23 for a single solid phase with the assumption that the solid is incompressible ... 

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