Systems, binary compound formation

Figure 5.6. Compound formation capability in the binary alloys of alkali metals. The different elements, the binary combinations of which with Li, Na, K, Rb, Cs are considered, are identified by their positions in the Periodic Table. No rehable data have been found about the stable equilibrium phases in the Na-P and Cs-As systems compound formation is, however, probable.

This applies to systems involving zinc or cadmium, on the one hand, and nitrogen or bismuth, on the other. For the remaining elements (Zn, Cd-P, As), the formation of solid solutions is most probable, owing to the strong interaction in the primary binary systems. The formation of variable phases based on antimony is predicted, but, because of the metastability of the binary compounds of the primary systems and also the absence of a structural analogy, the problem is complicated and requires a more detailed analysis. 

Chapter 12 - Spatial-energy criterion of structure stabilization was obtained. The computation results for a hundred binary systems correspond to the experimental data. The basic regularity of organic cyclic compound formation is given and its application for carbon nanostructures is shown. 

Figure 2.22. Compound formation capability in binary systems. The different element combinations are mapped on Mendeleev number coordinates and those systems are indicated in which the formation of intermediate phases has been observed (either from the liquid or in the solid state). Blank boxes indicate systems for which no certain data are available. Notice that the compound-forming alloys are crowded in a region corresponding to a large difference in the Mendeleev numbers of the elements involved (for instance, basic metals with semi-metals).

In the case of a ternary system, the formation of several, binary and ternary, stoichiometric phases, and different types of variable composition phases can be observed. One may differentiate between these phases by using terms such as point compounds (or point phases), that is, phases represented in the composition field by points, line phases , field phases , etc. 

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. 

Temperature, pressure, and concentration can affect phase equilibria in a two-component or binary system, although the effect of pressure is usually negligible and data can be shown on a two-dimensional temperature-concentration plot. Three basic types of binary system — eutectics, solid solutions, and systems with compound formation—are considered and, although the terminology used is specific to melt systems, the types of behaviour described may also be exhibited by aqueous solutions of salts, since, as Mullin 3-1 points out, there is no fundamental difference in behaviour between a melt and a solution. 

Consider the Mg-Ni binary phase diagram shown above. Note that in this system, inter-metallic compound formation is common for example, Mg2Ni, MgNi2 are stoichiometric compounds. 

As the author points out, the sulfuric acid-water system is one of the few examples of a liquid binary system in which certain properties change discontinuously. In this case dsjdp, where s is the specific gravity and p the per cent concentration of H2S04, has discontinuities at certain values of p. The most pronounced correspond to the compositions H2S04—H20 and H2S04—2H20. Mendeleev (102) believes that these characteristic points are connected with the formation in the solutions of definite chemical compounds. The more stable the compound the sharper the discontinuity in the property versus composition. 

Abstract—The equilibrium diagrams of the binary systems of sulphuric add with nitromethane and with o-y m- and p-nitrotoluene have been investigated. It has been shown that addition compounds of the type 1 1 are formed in these systems, analogous to the compound sulphuric acid-nitrobenzene (Chebbuuez Helv, Chim, Acta 1923 6 281 and Masson J. Chem. Soc. 1931 3201)t The formation of these addition compounds is due to hydrogen bonding between the components, rather than to proton transfer. Their stability in the crystalline phase seems to be contradictory to the known basicities of mononitrocompounds (Gillespie and Solomons J. Chem. Soc, 1957 1796), because of the effect of temperature on the equilibria in the liquid phase. 

The investigation of viscosities, electrical conductivities, refractive indexes and densities of binary liquid systems of sulphuric acid with nitromethane, nitrobenzene and 0-, m and p-nitrotoluene was made in order to obtain a clearer picture of the behaviour of these binary mixtures, regarding the stability of the addition compounds formed between the components. The application of these methods of physicochemical analysis to a number of binary systems with sulphuric acid [1, 2, 3] has enabled us to get some idea of the way in which the formation and stability of addition compounds affects the liquid phase properties of these systems. The binary systems of sulphuric acid with mononitrocompounds are particularly suitable for comparison with each other, because of the close similarity of the liquid media in these systems, due to comparable values of dielectric constants and liquid phase properties of the mononitrocompounds. The stability of the addition compounds in these systems in the crystalline phase [4] has... 

Figure 6-3. a) T-Nt and b) G-N, diagram of a binary system with (nonstoichiometric) compound y. The reaction path for isothermal compound formation is indicated by arrows (see text). 

J. B. Ott, J. R. Goates, and N. F. Mangelson, Solid-Liquid Phase Equilibria in Binary Mixtures of p-Dioxane with CCI4, CBrClj, and CFCI3. Solid Compound Formation in the CCI4 and CFCI3 Systems , J. Chem. Eng. Data, 9, 203-206 (1964). 

Of course, not all methods of cocrystal production require the use of auxiliary solvents. Thermal microscopy was used to determine if a particular carboxylic acid could cocrystallize with 2-[4-(4-chloro-2-fluorophe-noxy)phenyl]pyrimidine-4-carboxamide, with positive interactions being detected as crystalline material being produced at the binary interface [35]. Once identified, authentic cocrystal systems were prepared on a larger scale using solution-phase methods. In a similar study, hot-state microscopy was used to screen the possible interactions of nicotinamide with seven compounds of pharmaceutical interest that contained carboxylic acid groups [36]. A screening method for cocrystal formation based on differential scanning calorimetry has also been described, and used to demonstrate cocrystal formation in 16 out of 20 tested binary systems [37],... 

Similar to other binary /(-p-clcment systems, the formation of binary rare earth - antimonides with a simple stoichiometry is a characteristic feature of these systems. The largest number of structure types formed was encountered for the group of RSb2 compounds (4 members). The polymorphic modifications were observed for GdSb2 and TbSb2 as well as the RSb (R = La, Ce) and RsSb (R = Yb, Y and Sc) compounds were noted to undergo the solid state transformations. 

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