Crystals, mutual solubility

Silver and gold form a simple alloy system because they have nearly the same atomic diameters 2.89 and 2.88 Angstroms, respectively. Both have f.c.c. crystal structures, and both come from the same column of the Periodic Table so they are isoelectronic. The two metals are mutually soluble with a heat of mixing, AUm = -48meV/atom. The molecular volume, Vm = 8.5 x 10 24cm3, so the heat of mixing density, AUm/Vm is 90.4 x 108ergs/cm3. 

Nitrides are closely related to carbides. Several of them have the same NaCl crystal structure, and similar lattice parameters. Also, the carbide and nitride of the same metal are mutually soluble. Their hardnesses are similar. 

Indeed, in the world of tomorrow we can expect new aspects of polymer solids to extend the conventional and successful structure ideas of this century. These, of course, were the recognition as molecular identities of the chains of repeating chemical monomers. The circumstances of those entities have resulted in interesting concepts of solubilities, viscosity, and other mechanics, and especially thermodynamic limitations m mutual solubility or comparability of polymer mixtures. But we have known for decades that even homogeneous regular chain polymers such as Carothers polyesters and polyamides formed solids with manifold imperfections and irregularities, such as order-disorder crystal configurations.(22,23)... 

Figure 2.11. The Au-Si diagram is an example of a simple eutectic system with complete mutual solubility in the liquid state and no (or negligible) solubility in the solid state at a temperature of 363°C the liquid having the composition of 18.6 at.% Si solidifies with the simultaneous crystallization of the practically pure gold and silicon mechanically mixed. In the Cr-U system a slightly more complex situation due to the solid-state transformations of uranium is shown.

Almost all the crystalline materials discussed earlier involve only one molecular species. The ramifications for chemical reactions are thereby limited to intramolecular and homomolecular intermolecular reactions. Clearly the scope of solid-state chemistry would be vastly increased if it were possible to incorporate any desired foreign molecule into the crystal of a given substance. Unfortunately, the mutual solubilities of most pairs of molecules in the solid are severely limited (6), and few well-defined solid solutions or mixed crystals have been studied. Such one-phase systems are characterized by a variable composition and by a more or less random occupation of the crystallographic sites by the two components, and are generally based on the crystal structure of one component (or of both, if they are isomorphous). 

Although polymorphism in plastic crystals is less frequent than in liquid crystals, it does exist. Tetrakis(methylmercapto)methane, C(SCH3)4, for example, has four crystal modifications of which the three high temperature forms have a high degree of plasticity 100). Also, it has been observed that plastic crystals are frequently mutually soluble 16b), a consequence of the less restrictive crystal structures. Phase separation of these solutions occurs often on transition to the fully ordered crystal, giving rise to quite complicated phase diagrams102). 

Determine the appropriate operating temperature for the crystallizer. Figure 10.6 shows the mutual solubility of benzene and naphthalene. Most of the naphthalene can be crystallized by cooling to (i.e., operating the crystallizer at) the eutectic temperature of —3.5°C (25.7°F), where the solubility... 

Mutual solubility relationships are of great importance in many industrial processes. The principles of fractional crystallization are used... 

If the monomer and polymer are not mutually soluble, the bulk reaction mixture will be heterogeneous. The high pressure free radical process for the manufacture of low density polyethylene is an example of such reactions. This polyethylene is branched because of self-branching processes illustrated in reaction (6-89). Branches longer than methyls cannot fit into the polyethylene crystal lattice, and the solid polymer is therefore less crystalline and rigid than higher density (0.935-0.96 g cm ) species that are made by coordination polymerization (Section 9.5). 

Impurities, i.e. components chemically different from the constituents which form the perfect crystal structure, may be accommodated in the structure, in similar ways to the above, provided that the atoms, ions or molecules of the additive are chemically compatible with those of the host phase. This usually means that their size, shape and bonding properties are similar to those of the constituents of the host material. Incorporation is a specific process. Some binary, or more complex, combinations have only restricted ranges of mutual solubility, while other mixtures are capable of forming the complete range of intermediate solid solutions from 100%Ato 100%B. 

SO that the curve is in agreement with the results obtained by A. Fock, but not with those of M. Herz. The mutual solubility of the two salts in the solid state is complete and the more soluble salt is always in greater proportion in the soln. than in the crystals. The solubility curve of potassium chromate and molybdate is similar. L. Stibing gave for mixtures of potassium sulphate and chromate in soln. and solid soln., when the composition is expressed in molar per cent. K2Cr04 per litre ... 

First, there is only a very small mutual solubility of the elements and, second, one finds a strong tendency to de-mix even if only one crystal structure is considered, reflected by the "camel back" curves for each of the solid phases. In other words, even if there were no structural differences between Sn and Zn, they would immediately de-mix. The "camel back" is also observed for the liquid phase ( ) such that Sn and Zn behave in a strongly xenophobic way to each other. In classical terms, Sn and Zn de-mix because of the very positive mixing enthalpies for each of the phases. These enthalpies AH (with reference to the respective pure solid elements) are shown in Figure 3.50(a), and all three curves AH vs. X were calculated from the above Gibbs energy data by taking the appropriate temperature derivatives. 

The suitability of the amines diisopropylamine (DiPA) and dimethylisopropylamine (DMiPA) as antisolvents for the crystallization of sodium chloride from its aqueous solution has been demonstrated. Both amines decreased the sodium chloride solubility substantially. The presence of a two liquid phase area offered the opportunity to separate the amines from the mother liquor after crystallization by a temperature increase. In the two liquid phase area the mutual solubilities of the water and the amines were low, so the separability was good. Continuous crystallization experiments were carried out at temperatures below the liquid-liquid equilibrium line in the single liquid phase area. The product consisted of cubic agglomerated NaCl crystals with maximum primary particle sizes of 10-70 pm. 

The amines DiPA and DMiPA are suitable candidates for the antisolvent crystallization of sodium chloride. Both amines reduce the sodium chloride solubility substantially. At the antisolvent recovery conditions the mutual solubilities of the water and the amines were low, so the separability after crystallization was generally good. 

Boron-based ternary phase diagrams with two transition metals have been investigated for exploitation of the diborides with an AIB2 structure, which have high hardness and a high melting point. Due to the identical crystal structure, most of the transition metal diborides have been considered of high mutual solubility... 

Figure 11.12 shows the proposed scheme for the stractural evolution during the synthesis, based in a liquid-crystal templating (LCT) mechanism. Initially, the aqueous acid solution is solubihzed in the cyhndrical reverse micelles forming the reverse hexagonal phase. Nonhydrolyzed TEOS molecules and PDMS chains are mutually soluble and therefore constitute the hydrophobic continuous medium. The hydrolysis is probably driven by interfacial diffusion of the water towards the... 

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