Mixtures solid solution formation

The composition of the equilibrium mixture shows that Br has been enriched significantly in the solid phase in comparison to the liquid phase (D > 1). If one considered the concentrations of aqueous [Br"] and [Ag+], one would infer, by neglecting to consider the presence of a solid solution phase, that the solution is undersaturated with respect to AgBr ([Ag+] [Br ]/KsoA Br = 0.1). Because the aqueous solution is in equilibrium with a solid solution, however, the aqueous solution is saturated with Br. Although the solubility of the salt that represents the major component of the solid phase is only slightly affected by the formation of solid solutions, the solubility of the minor component is appreciably reduced. The observed occurrence of certain metal ions in sediments formed from solutions that appear to be formally (in the absence of any consideration of solid solution formation) unsaturated with respect to the impurity can, in many cases, be explained by solid solution formation. 

Monotectic mixtures arise when the individual components have similar melting points, molecular volumes and polymorphic forms. Figure 17.12(a) represents a possible phase diagram for monotectic mixtures. A typical monotectic solution occurs when SSS is mixed with SOS. Lutton (1955) determined that the a form was present and associated with limited solid solution formation, and contrasted with the a forms of other glyceride mixtures that formed continuous solid solutions (Rossell 1967). It was found, for this system, that tristearin incorporates about 50% of the SOS into a solid solution on the other hand, SOS incorporates very little SSS into a solid solution. 

For a mixture of 10" Af iodide and 10" Af bromide, calculate the theoretical percentage error in titration of the iodide and the bromide with AgNOa, neglecting dilution and solid-solution formation. TakeATsp Agi = 10" , A ,p.AgBr = 4 X 10- 3... 

Because of the extieme reactivity of MoW(0200(0113)3)4, chromatographic methods for sepaarting the mixture were very difficult to apply. Thus it was not possible to obtain the pure, neutral mixed-metal compound. However, this greater reactivity could be advantageous in preparing a pure mixed-metal compound. It was natural to investigate the reaction with iodine with the expectation that the mixed-metal compound would react preferentially if a limited quantity of oxidant was available. The success of the method exceeded expectations, but it was surprising that a simple iodide salt was obtained rather than the triiodide salt as with the dimolybdenum compounds. This difference probably facilitates separation since the possibility of solid-solution formation between oxidized products is diminished. 

Solid solution formation, where two or more components form one crystal lattice over a continuous range of compositions, is frequently observed in dye and pigment chemistry l As a consequence, the X-ray diffraction pattern of such a solid solution is the same or very similar to that of one of the components, the host. In analogy to liquid solutions, the guesf molecules are dissolved into the crystal lattice of the hosf. In some cases this can also lead to a variation of the coloristic and other properties compared to a physical mixture of the individual pigments. A special case of solid solutions is a mixed crystal, where a specific composition containing two components results in a unique diffraction pattern different from the XRD of either of the components. In this case, a loose analogy can be drawn to the formation of azeotropes in the liquid state. Both cases have been observed within DPP chemistry. 

Later, it was shown that the phenomenon of solid solution formation is widespread in this family of pigments. The previously discussed scarlet pigment 4,11-dichloroquinacridone was greatly improved in weatherfastness by solid solution formation (P.R. 207, CAS 71819-77-7 ) with the parent compound. In this case the approximate composition is also two moles of quinacridone and one mole of the substituted counterpart, retaining largely the scarlet color of the latter and the photochemical stability of the former. The X-ray diffraction pattern of the solid solution is different from that of a mixture of the two ingredients (Figure 18-12) or those of the individual components. As in most cases, while the X-ray diffraction pattern of a mixture is simply additive and predictable, the solid solution shows a non-additive diffraction pattern and an unpredictable color effect. 

Similarly, quinacridone forms solid solutions with 2,9-dimethyl or 2,9-dichloroquina-cridone at about a ratio of two moles of unsubstituted to one mole of the substituted compound, the X-ray diffraction patterns of which are virtually identical and are different from those of mixtures of the individual ingredients (Figure 18-13). One blue-shade red is an article of commerce (P.V. 42, CAS 71819-79-9. In fact, using quinacridone and three 2,9-disubstituted derivatives, a series of binary and ternary solid solutions are formed, as depicted in Figure 18-14. The large triangle is subdivided into four smaller triangles and the areas where binary and ternary solutions are possible are shown. It is obvious that solid formation is unpredictable and requires numerous experimental determinations to delineate areas of solid solution formation. 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Since the values of the unit cell parameter of the acidic salts were not intermediate between those of the neutral salts and of the parent acid (ao = 1.216 and 1.217 nm, respectively, for H3PWX2O40 and H4SiWi204o), one may propose that there is no formation of solid solutions but rather a mixture of the neutral salt and of the acid highly dispersed on the neutral salt. 

Stabilization of Ru based oxides by valve metal oxides has not been studied in such detail using photoelectron spectroscopy. The most common compositions, however, with relatively high valve metal content, are not in favor of formation of a solid solution. Studies of the phase formation in Ru/Ti mixed oxides has shown [49] that homogeneous solutions are formed for compositions with Ru < 2% or Ru > 98% (see Section 3.1.1). Therefore electrodes with other compositions are better described as physical mixtures and the electrochemical behaviour is most likely that of a linear superposition of the single components. It has to be considered, however, that the investigations performed by Triggs [49] concern thermodynamic equilibrium conditions. If, by means of the preparation procedure, thermodynamic equilibrium is... 

Alloys of copper and zinc can be obtained by combining the molten metals. However, zinc is soluble in copper up to only about 40% (of the total). When the content of a copper/zinc alloy contains less than 40% zinc, cooling the liquid mixture results in the formation of a solid solution in which Zn and Cu atoms are uniformly distributed in an fee lattice. When the mixture contains more than 40% zinc, cooling the liquid mixture results in the formation of a compound having the composition CuZn. The solid alloy consists of two phases, one of which is the compound CuZn and the other is a solid solution that contains Cu with approximately 40% Zn dissolved in it. This type of alloy is known as a two-phase alloy, but many alloys contain more than three phases (multiple-phase alloys). 

Theoretical (dotted line) and experimental (continuous line) titration curves for such a mixture are shown in Figure 6.8(b). The formation of mixed crystals and solid solutions limits the accuracy to 1-2% when the halides are present in similar concentrations. 

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