Solution miscible solid

When two partially miscible solid solutions are formed there will be three phases present, and the system will be univariant. At constant temperature the pc curwt will be a straight line, as in the case of the formation of a compound. The behaviour of this system will, therefore, also be represented diagrammatically by Fig. 20. 

II. [d) Absorption of Gas and Formation of Two Partially Miscible Solid Solutions. 

I. Two Gaseous Components. II. a). A Gaseous and a Solid Component which can form Compounds. Ammonia compounds of metal chlorides. Formation of oxy-carbonates. Salts with water of crystallisation. Efflorescence. Indefiniteness of the vapour pressure of a hydrate. Suspended transformation. Eange of existence of hydrates. Constancy of vapour pressure and the formation of compounds. II. (6). The Gas is Absorbed BY THE Solid Component and No Compound is Formed. II. ( ). The Gas is Absorbed by the Solid Component and a Compound is also Formed. II. d). Absorption of Gas and Formation of T-wo Partially Miscible Solid Solutions. Palladium and hydrogen. 

Not all solid solution systems form continuous series some exhibit partial miscibility, i.e. one solid solution being partially miscible with another, and, as in the case of partially miscible liquids, the phase region between the two homogeneous phases is referred to as the miscibility gap. Partially miscible solid solution systems can exhibit a number of different types of behaviour, but only one simple case will be described here for illustration purposes. 

K) and copper and gold form a completely miscible solid solution (gold s 0o = 165 K), when the other physical properties of these two metals (silver and gold) are essentially identical. 

These generally gave two-phase blends with PIB and butyl rubber. Properties vs polyblend ratio usually indicated that these phases were partially miscible solid solutions [77]. Crosslinked phases increased stability of morphology and properties [26]. Intensive studies of HDPE -I- Butyl blends gave bimodal peaks for melt viscosity and ultimate elongation vs blend ratio, which were explained by two continuous laminar/fibrillar phases [188]. 

Some alloys are composed of metals that have different crystal structures. For example, nickel crystallizes in the face-centered cubic structure and chromium in the body-centered cubic structure. Because of their different structures, these two metals do not form a miscible solid solution at all compositions. At some intermediate composition, the structure has to change from that of one of the metals to that of the other. Figure 23.7 shows the nickel and chromium phase diagram from 700 °C to 1900 °C. Notice that the diagram has two different solid phases face-centered cubic and body-centered cubic. From pure nickel (0 mol % chromium) to about 40-50 mol % chromium, the structure is face-centered cubic. 

If the two metals in an alloy are similar in size and have the same crystal structure, they tend to form a miscible solid solution, which means that they can form an alloy at any composition ratio. If the two metals are dissimilar in size or crystal structure, the solubility of one atom in the other s crystal structure is often limited. At certain compositions two different crystals can coexist in equilibrium this is called a two-phase region. The lever rule determines which phase is present in a greater proportion. 

Figures 56.3a and 56.3b demonstrate cases of partial and total solid-state miscibility of the undesired salt in the desired salt, respectively. For the case of partial miscibility, solid solutions enriched with the desired salt (but not the pure desired salt) can be obtained and separation efficiency for a system at point P can be calculated as c = 2 (RO/WO) = Xw [(1-2Xo)/(l-Xo)]. where Xw represents for the...

Figure 8.20 SLE in solid solutions, (a) The solid solution is inisdble in aU proportions (b) a partially miscible solid solution.

Solvent power characterizes the miscibility of solute and solvent. This concept covers two types of uses dissolving a solid or reducing the viscosity of a liquid. The solvent power should be as high as possible. However, a solvent used as an extractant should also be selective, i.e., extract certain substances preferentially from the feed being treated. 

The general case of two compounds forming a continuous series of solid solutions may now be considered. The components are completely miscible in the sohd state and also in the hquid state. Three different types of curves are known. The most important is that in which the freezing points (or melting points) of all mixtures lie between the freezing points (or melting points) of the pure components. The equilibrium diagram is shown in Fig. 7, 76, 1. The hquidus curve portrays the composition of the hquid phase in equihbrium with sohd, the composition of... 

Calcium is miscible with Sr in the liquid and in all the solid bcc, hep and fee allotropic forms (Fig. 1). Barium exhibits no hep or fee forms, however, so that solid solubility between the close-packed structures of Ca and Sr, and the bcc structure of Ba is restricted in the Ca-Ba and also in the Sr-Ba systems. A continuous series of solid solutions is only achieved in Ca-Ba and Sr-Ba for the high-T bcc modifications. In Ca-Ba, the solid solutions are separated by a narrow heterogeneous field between 32 and 36 mol% Ba in Sr-Ba this occurs between 24 and 30 mol% Ba (Fig. 1). 

The phase diagram for aluminum/silicon (Fig. 4.5) is a typical example of a system of two components that form neither solid solutions (except for very low concentrations) nor a compound with one another, but are miscible in the liquid state. As a special feature an acute minimum is observed in the diagram, the eutectic point. It marks the melting point of the eutectic mixture, which is the mixture which has a lower melting point than either of the pure components or any other mixture. The eutectic line is the horizontal line that passes through the eutectic point. The area underneath is a region in which both components coexist as solids, i.e. in two phases. 

Two kinds of solid solutions crystallize, a solution of metal 1 in metal 2 and vice versa (limited miscibility). 

Two metals that are chemically related and that have atoms of nearly the same size form disordered alloys with each other. Silver and gold, both crystallizing with cubic closest-packing, have atoms of nearly equal size (radii 144.4 and 144.2 pm). They form solid solutions (mixed crystals) of arbitrary composition in which the silver and the gold atoms randomly occupy the positions of the sphere packing. Related metals, especially from the same group of the periodic table, generally form solid solutions which have any composition if their atomic radii do not differ by more than approximately 15% for example Mo +W, K + Rb, K + Cs, but not Na + Cs. If the elements are less similar, there may be a limited miscibility as in the case of, for example, Zn in Cu (amount-of-substance fraction of Zn maximally 38.4%) and Cu in Zn (maximally 2.3% Cu) copper and zinc additionally form intermetallic compounds (cf. Section 15.4). 

Gold forms a continuous series of solid solutions with palladium, and there is no evidence for the existence of a miscibility gap. Also, the catalytic properties of the component metals are very different, and for these reasons the Pd-Au alloys have been popular in studies of the electronic factor in catalysis. The well-known paper by Couper and Eley (127) remains the most clearly defined example of a correlation between catalytic activity and the filling of d-band vacancies. The apparent activation energy for the ortho-parahydrogen conversion over Pd-Au wires wras constant on Pd and the Pd-rich alloys, but increased abruptly at 60% Au, at which composition d-band vacancies were considered to be just filled. Subsequently, Eley, with various collaborators, has studied a number of other reactions over the same alloy wires, e.g., formic acid decomposition 128), CO oxidation 129), and N20 decomposition ISO). These results, and the extent to which they support the d-band theory, have been reviewed by Eley (1). We shall confine our attention here to the chemisorption of oxygen and the decomposition of formic acid, winch have been studied on Pd-Au alloy films. 

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. 

Positive deviations from ideal behaviour for the solid solution give rise to a miscibility gap in the solid state at low temperatures, as evident in Figures 4.10(a)-(c). Combined with an ideal liquid or negative deviation from ideal behaviour in the liquid state, simple eutectic systems result, as exemplified in Figures 4.10(a) and (b). Positive deviation from ideal behaviour in both solutions may result in a phase diagram like that shown in Figure 4.10(c). 

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