Immiscibility solids

Eutectic diagrams (from Greek svtt]ktoo- easily melted ) represent the T-x melting behavior for binary systems with completely immiscible solid phases a, /3. The solid a, /3 phases often correspond to (virtually) pure components A, B, respectively, so we may treat phase and component labels (rather loosely) as interchangeable in this limit. 

In Chapter 8, the simple case of totally immiscible solids, exhibiting a minimum melting eutectic, was discussed. There are a variety of other behaviors that can be demonstrated in solid-liquid equilibria. For example, a solid solution may be formed. In a solid solution, the arrangement of atoms shows some degree of randomness on the molecular level. This occurs in a substitutional solid solution, where the components are very similar and can substitute for each other in the solid lattice. Although the lattice is regular, which atoms in the lattice are substituted is random. (If the substitution were periodic, the system would be a compound.) Copper and nickel illustrate this behavior and form a substitutional solid solution at all concentrations. Another type of solid solution is an interstitial... 

For pure bcc or fee metals, experimental values of crsv and nearest-neighbour interaction model of Skapski (1956) (see Section 5.1). Usually, Pure metals and A-B alloys is of the order of 102 mJ/m2. However, for some highly immiscible solid A/liquid B systems, values of [Pg.164]

Oxysulfides are also rather important. Y2O2S is used as a host material for Ln + ion emitters (e.g. Eu, Tb) in some phosphors, notably those used in TV screens. When mischmetal is used to remove oxygen and sulfur from impure iron and steel, the product is an oxysulfide, which forms an immiscible solid even in contact with molten steel and thus does not contaminate the product. 

Figure 14.21 Txz diagrams.(a) Case I, ideal liquid and solid solutions (b)Case II, ideal liquid solution immiscible solids...

Figure 2. Depression of eutectic melting point by a supercritical fluid in an A-B-SCF system, where A,B are immiscible solids and Pj < Pa < Ps- 5 upper lines represent first freezing and the lower lines represent first melting (o Pi A - Pa, - Ps) ...

What is the interpretation to be put on these curves With regard to the two end portions, these represent bivariant, two-phase systems, consisting of a solid solution and gas. They correspond, therefore, to curve AB in Fig. 20 (p. 73). If the middle portion were horizontal, it would indicate either the formation of a compound or of two immiscible solid solutions. If a compound Pd2H were formed, then the middle portion would at all temperatures end at the same value of the concentration, viz. that corresponding to 0 5 atom of hydrogen to... 

In Fig. 9.26, the thermodynamic equilibrium, solid-liquid phase diagram of a binary (species A and B) system is shown for a nonideal solid solution (i.e., miscible liquid but immiscible solid phase). The melting temperatures of pure substances are shown with Tm A and Tm B. At the eutectic-point mole fraction, designated by the subscript e, both solid and liquid can coexist at equilibrium. In this diagram the liquidus and solidus lines are approximated as straight lines. A dendritic temperature T and the dendritic mass fractions of species (p)7(p)s and (p)equilibrium partition ratio kp is used to relate the solid- and liquid-phase mass fractions of species (p)7(p)J and (p)f/(p)f on the liquidus and solidus lines at a given temperature and pressure, that is,... 

In this section we consider a two-component system consisting of a liquid mixture and three immiscible solid phases pure solids 1 and 2 and a compound of composition (A",)v,(2G)v2- The temperature-composition diagram of this system is represented in Fig. 9-11. In this case, phase 1 is the liquid mixture and phase 2 is pure solid 1, pure solid 2, or solid compound of mole fraction )>2 = y = + 2). 

Phare diagram for a binary system of immiscible solids and (bdr complcicly miscilile... 

Let it be supposed, in the first place, that there are three phases present, namely, zinc oxide and carbon as immiscible solids, and a vapour phase consisting of CO, CO2 and zinc vapour. (The possibility of forming liquid zinc as a fourth phase will be discussed later.) The system would therefore be divariant if it were an entirely arbitrary mixture of the five species in question. However, the fact that it is prepared from zinc oxide and carbon implies a stoichiometric restriction on the composition of the vapour phase for every atom of zinc vapour there must be one atom of combined oxygen as CO or CO2. 

Let it be assumed, in the fimt place, that the system is prepared from zinc sulphide and from pure oxygen, in place of air. There are thus six species in all, and, since there are three independent reactions, there are three components. Assuming that the oxide, sulphide and sulphate are present as immiscible solids, there are four phases and the system is therefore univariant. 

In Section 3.3.7.S, the equilibrium partitioning of a species between a liquid phase and a solid phase was briefly considered for three types of liquid-solid equilibria. The separation between two species i and j for such liquid-solid two-phase systems is briefly considered here. There are systems where three phases can be present for example, two immiscible solid phases and a saturated solution, as in the case of solid salt, ice and a saturated salt solution. Figure 4.1.10 shows a temperature vs. composition phase diagram where solid phase 1 coexists with solid phase 2 and a saturated liquid solution at the eutectic point E. Below the eutectic temperature T, immiscible pure solid phase 1 and 2 are present together. For these and more complex systems, the reader should refer to appropriate texts (Darken and Gurry, 1953 DeHoff, 1993). Separation between species i and j in simpler two-phase systems described in Figures 3.3.6A, where the solid phase is a homogeneous solution, will be determined now. 

A positive heat of mixing in the solid phase tends to lower the solidus curve and will eventually result in solid immiscibility at low temperatures. If this heat of mixing is large enough for the solid-solid immiscibility to occur in the vicinity of the melting points of the pure components, a eutectic reaction may occur in which a melt at a certain composition and temperature may transform into two immiscible solids or s5mibolically L Si + S2 or L <-> a + (3. A similar reaction called a eutectoid reaction can also occur in the solid state in which -y a -T (3. 

The migration of additives—and hence their possible elimination—depends on the strength of polymer-additive interactions and on their molar mass, especially when they are organic substances (evaporation of volatile molecules) their physical state also matters (immiscible solids do not migrate easily). Additives with low vapor pressure and that afford homogeneous blends because of a negative interaction parameter (X12) are always preferred. 

FIGURE 6.25 Loss angle, 5, as a function of temperature for various types of polymer blends (a) miscible (dashed line), (b) immiscible (solid line), and (c) partially miscible (dotted line). The glass transition temperature, Tg, is the temperature at the peak of the loss angle. 

Figure 8.17 SLE in pure, immiscible solids, (a) Binary solution of a and b (b) a compound ajj forms.

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