Phase diagrams binary eutectic systems

Figure 12.8 Phase diagram for a binary eutectic system (Gill, 1994).

Figure 3.20. Phase diagram of the simple binary eutectic system.

The use of the differential thermal analysis in the phase diagram determination is illustrated in Figure 3.52. A hypothetical binary eutectic system A-B with the formation of the incongmently melting compound A4B was chosen. There are three thermograms (a) to (c) shown as examples. In thermogram (a), the first heat effect at temperature ai... 

The simple crystallization of a binary eutectic system only produces one of the components in pure form, while the residual mother hquor composition progresses towards that of the eutectic (section 4.3.1). There is often a need, however, to produce both components in pure form, and one way in which this may be achieved is to add a third component to the system which forms a compound with one of the binary components. Phase diagrams for systems with compound formation are discussed in section 4.3.2. 

In Figure 8.2-9 the phase diagram for an eutectic solidifying binary nrixture is shown. According to the given phase diagram (binary system without formation of mixed crystals) this soUd should contain less A than the feed. In this case the thermodynamic distribution coefficient for an impurity component i is defined by... 

Equations (1.76) and (1.77), together with Equations (1.45)and(1.46), indicate that similar information may be expressed in terms of activity. For cases where a two-phase mixture is stable, (Figure 1.6(b)), Equations (1.76) and (1.77) indicate that the activities are constant across the two-phase field. Figure 1.7 illustrates the above points and their relationship to the conventional T versus Xphase diagram for a hypothetical binary eutectic system. 

Figure 1.8 presents the phase equilibria in a hypothetical binary eutectic system similar to that in Figure 1.7, represented on each of the three types of diagrams. This diagram is similar to those for the Ag-Cu and Ni-Cr systems. The plot of T versus ub is a Type 1 diagram and the three-phase equilibrium a-L-(3 is represented by a point. The plot of T versus Ab is a Type 2 diagram and the a-L-(3 equilibrium is represented by three points on a line, the eutectic isotherm. The plot of S versus Xb is a Type 3 diagram and the a-L-(3 equilibrium is represented by an area. Note that the forms of these diagrams correspond to those for the unary system in Figure 1.4. (Numerous examples of the three types of phase diagrams are given for unary, binary and ternary systems in Chapter 13 of Reference [2], Reference [5] and Chapter 2 of Reference [8].

Depending on composition, several different types of microstructm-es are possible for the slow cooling of alloys belonging to binary eutectic systems. These possibilities will be considered in terms of the lead-tin phase diagram. Figure 9.8. 

A typical example of a phase diagram with coexisting phases is a binary eutectic system such as that of Pb and Sn, commonly used in solders. The Pb-Sn phase diagram is shown in Figure 4.8. There are a number of features to notice. First, both Pb and Sn can dissolve some of the other element in their solid form, but Pb can dissolve much more Sn and this solubility persists to much lower temperatures than for solubility of Pb in Sn. Second, at temperatures below 181°C (the horizontal line on the figure) the system consists of a mixture of solid phases of Pb and Sn or a solid... 

Binary Alloys. Aluminum-rich binary phase diagrams show tliree types of reaction between liquid alloy, aluminum solid solution, and otlier phases eutectic, peritectic, and monotectic. Table 16 gives representative data for reactions in tlie systems Al—Al. Diagrams are shown in Figures 10—19. Compilations of phase diagrams may be found in reference 41. 

The distribution-coefficient concept is commonly applied to fractional solidification of eutectic systems in the ultrapure portion of the phase diagram. If the quantity of impurity entrapped in the solid phase for whatever reason is proportional to that contained in the melt, then assumption of a constant k is valid. It should be noted that the theoretical yield of a component exhibiting binary eutectic behavior is fixed by the feed composition and position of the eutectic. Also, in contrast to the case of a solid solution, only one component can be obtained in a pure form. 

OC10H21)], in which rearrangement does not occur. All the mixtures studied display liquid crystal behavior with improved properties with respect to the pure components. A representative binary phase diagram and their corresponding DSCtraces are presented in Figures 8.24 and 8.25 respectively, and reveal the eutectic nature ofthese systems. 

A brief discussion of sohd-liquid phase equihbrium is presented prior to discussing specific crystalhzation methods. Figures 20-1 and 20-2 illustrate the phase diagrams for binary sohd-solution and eutectic systems, respectively. In the case of binary solid-solution systems, illustrated in Fig. 20-1, the liquid and solid phases contain equilibrium quantities of both components in a manner similar to vapor-hquid phase behavior. This type of behavior causes separation difficulties since multiple stages are required. In principle, however, high purity... 

There are many types of phase diagrams in addition to the two cases presented here these are summarized in detail by Zief and Wilcox (op. cit., p. 21). Solid-liquid phase equilibria must be determined experimentally for most binary and multicomponent systems. Predictive methods are based mostly on ideal phase behavior and have limited accuracy near eutectics. A predictive technique based on extracting liquid-phase activity coefficients from vapor-liquid equilibria that is useful for estimating nonideal binary or multicomponent solid-liquid phase behavior has been reported by Muir (Pap. 71f, 73d ann. meet., AIChE, Chicago, 1980). 

Figure 6.10. A generic binary phase diagram is shown for an A-B system in which two compounds, AB and ABm, are formed. Different parts of the liquidus line are indicated. 1 is the line of primary crystallization of the terminal solid-solution based on the component A (which, on cooling, will be followed by the peritectic formation of AB ) 2 is the line of primary crystallization of the compound AB (to be followed by the eutectic crystallization of AB + ABm) 3 and 4 are lines of primary crystallization of ABm (to be followed, respectively, by the crystallization of the eutectic AB + ABm or of the eutectic AB, + B-based solid solution).

Figure 15.4. Phase diagrams for binary systems (E - eutectic, L - liquid)...

A melt is a liquid or a liquid mixture at a temperature near its freezing point and melt crystallisation is the process of separating the components of a liquid mixture by cooling until crystallised solid is deposited from the liquid phase. Where the crystallisation process is used to separate, or partially separate, the components, the composition of the crystallised solid will differ from that of the liquid mixture from which it is deposited. The ease or difficulty of separating one component from a multi-component mixture by crystallisation may be represented by a phase diagram as shown in Figures 15.4 and 15.5, both of which depict binary systems — the former depicts a eutectic, and the latter a continuous series of solid solutions. These two systems behave quite differently on freezing since a eutectic system can deposit a pure component, whereas a solid solution can only deposit a mixture of components. 

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