Eutectic type

Column crystalhzers of the end-fed type can be used for purification of many eutectic-type systems and for aqueous as well as organic systems (McKay loc. cit.). Column ciystaUizers have been used for xylene isomer separation, but recently other separation technologies including more efficient melt ciystaUization equipment have tended to supplant the Phillips style ciystaUizer. 

No chalcogenide halides of zinc and cadmium are known. The phase diagrams of CdS-CdCl (7, 198, 210), CdSe-CdCl (220, 314), CdTe-CdClj 368), CdTe-CdBr2 (368), and CdTe-Cdl (323) are of a simple, eutectic type. The system CdS-CdCl shows a range of solubility of CdS in solid CdClj that extends to 5% of CdS at room temperature, and increases to a maximum of 12.5% of CdS at 500°C (7,210). 

Safonov et al. 330) also investigated the In-Te-I system by DTA and X-ray diffraction. The system contains three, congruently melting, ternary compounds InTel, Inl3-2Tel4 and InIs-STel, of which the latter two are out of the scope of this review. InTel melts congruently at 475°C. It forms part of the quasibinary cuts In Tea-Inla and Inl-Te, where the sections InTel-In Tes, InTel-Inia, InTel-Ini, and InTel-Te are all of the eutectic type (80). 

In the system Ti-W the continuous solid solution stable at high temperature decomposes on lowering the temperature through a eutectic-type reaction into... 

Figure 2.13. Building blocks of binary phase diagrams examples of three-phase (invariant) reactions. In the upper part the general appearance, inside a phase diagram, of the two types of invariant equilibria is presented, that is, the so-called 1 st class (or eutectic type) and the 2nd class (or peritectic type) equilibria. In the lower part the various invariant equilibria formed by selected binary alloys for well-defined values of temperature and composition are listed. In the Hf-Ru diagram, for instance, three 1 st class equilibria may be observed, 1 (pHf) — (aHf) + HfRu (eutectoid, three solid phases involved), 2 L — (3Hf + HfRu (eutectic), 3 L —> HfRu + (Ru) (eutectic).

The Te-S system is peculiar it is a simple eutectic-type diagram and shows (like an island completely surrounded by the single-phase field of the liquid) a small oval insolubility region situated between —37 and 41.5 at.% S and between two critical temperatures (upper Tc = 740°C and lower Tc = 690°C). This behaviour (often observed for instance in organic systems) among the different pairs of elements has been described only for Te-S. 

For the niobium-copper system different phase diagrams of the simple eutectic type (with the eutectic point very close to Cu) have been proposed, either with an S-shaped near horizontal liquidus line or with a monotectic equilibrium. It was stated that the presence of about 0.3 at.% O can induce the monotectic reaction to occur, whereas if a lesser amount of oxygen is present no immiscibility gap is observed in the liquid. 

The treatment above is the traditional derivation of the Scheil equation. However, it is not possible to derive this equation, using the same mathematical method, if the partition coefficient, k, is dependent on temperature and/or composition. The Scheil equation is applicable only to dendritic solidification and cannot, therefore, be applied to eutectic-type alloys such Al-Si-based casting alloys, or even for alloys which may be mainly dendritic in nature but contain some final eutectic product. Further, it cannot be used to predict the formation of intermetallics during solidification. 

If the surfactants have a more dissimilar structure or if the counterion is different with the same surfactant ion (e.g., sodium dodecyl sulfate and calcium dodecyl sulfate), the Krafft temperature of the mixture can be much less than either pure component (87—89) These systems show the classical eutectic type behavior and the crystals contain only one kind of surfactant or counterion in substantial amounts (87-89). 

In the case of non—eutectic systems, the solid phase shows nearly ideal mixing, so that the surfactant components distribute themselves between the micelle and the solid in about the same relative proportions (i.e., both the mixed micelle and mixed solid are approximately ideal). However, in the case of the eutectic type system, the crystal is extremely non-ideal (almost a single component), while the micelle has nearly ideal mixing. As seen in earlier calculations for ideal systems, even though the total surfactant monomer concentration is intermediate between that of the pure components, the monomer concentration of an individual component decreases as its total proportion in solution decreases. As the proportion of surfactant A decreases in solution (proportion of surfactant B increases) from pure A, there is a lower monomer concentration of A. Therefore, it requires a lower temperature or a higher added electrolyte level to precipitate it. At some... 

As explained previously, electrodissolution in ionic liquids is a simple and efficient process, particularly in chloride-based eutectics. Type III eutectics based on hydrogen bond donors are particularly suitable for this purpose. However, it has been noted that the polishing process only occurs in very specific liquids and even structurally related compounds are often not effective. It has been shown that 316 series stainless steels can be electropolished in choline chloride ethylene glycol eutectics [19] and extensive electrochemical studies have been carried out. The dissolution process in aqueous solutions has been described by two main models the duplex salt model, which describes a compact and porous layer at the iron surface [20], and an adsorbate-acceptor mechanism, which looks at the role of adsorbed metallic species and the transport of the acceptor which solubilises... 

Gvozdeva, L. I., and A. P. Lyubimov The Structure of the Liquid Eutectics and the Nature of the Viscosity composition diagram in Eutectic-Type Systems. Sb. Mosk. Inst. Stali i Splavov 41, 161 (1966). 

The behavior of aqueous solutions during freezing is much more complicated. At low cooling rates (1 to 5 K/min), crystallization in the water-salt system is thermodynamically controlled and can be satisfactorily described by the rules of eutectic crystallization, as most of these systems have eutectic-type phase diagrams (Figure 4.6). If the solution concentration is below the eutectic point (which is the usual case for most of the solutions used), crystallization of ice will be observed at T < T, followed by a systematic increase in concentration of the remaining solution until T, and simultaneous crystallization of ice and salt at T < Tg (Figure 4.6, line 1). For a solution with a eutectic concentration, only the last process will be observed (Une 2). 

Many SCWO applications involve mixtures of different salts. In such cases eutectic-type phenomena can occur, with broader regions of liquid phase behavior than with water-single salt systems. Further discussion of supercritical water systems containing mixed salts may be found in Hodes et al. ... 

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