Simple eutectic systems

In the case of a simple eutectic system shown in Fig. 22-2, a pure solid phase is obtaiuea by cooling it the composition oFthe feed mix-... 

Of the elements normally present in tin-rich alloys, lead forms a simple eutectic system with a eutectic composition at 63% Sn, and copper and antimony have a small solid solubility and form the intermetallic compounds Cu Sn, and SbSn respectively. ... 

In the case of a simple eutectic system shown in Fig. 20-2, a pure solid phase is obtainecf by cooling if the composition of the feed mixture is not at the eutectic composition. If liquid composition is eutectic, then separate crystals of both species will form. In practice it is difficult to attain perfect separation of one component by crystallization of a eutectic mixture. The solid phase will always contain trace amounts of impurity because of incomplete solid-liquid separation, slight solubility of the impurity in the solid phase, or volumetric inclusions. It is difficult to generalize on which of these mechanisms is the major cause of contamination because of analytical difficulties in the ultrahigh-purity range. 

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). 

Figure 2.11. The Au-Si diagram is an example of a simple eutectic system with complete mutual solubility in the liquid state and no (or negligible) solubility in the solid state at a temperature of 363°C the liquid having the composition of 18.6 at.% Si solidifies with the simultaneous crystallization of the practically pure gold and silicon mechanically mixed. In the Cr-U system a slightly more complex situation due to the solid-state transformations of uranium is shown.

Figure 9.1. Simple eutectic system with ideal mixing in the liquid and negligible solid solubility in the terminal solid phases, a and / .

The SEE diagram for a longer alkyl chain IL (2-hydroxy-ethyl)dimethyl undecyloxymethylammonium dicyanamide, [CnOCiEtOH(Ci)2N][dca] (1) in 1-octanol presents a typical SLE/LLE phase diagram—a simple eutectic system with immiscibility in the liquid phase with the UCST. The influence of the [dca] anion in spite of the long alkyl chain makes this salt liquid at room temperature = 283.5 K). Therefore, the choice of the anion can have a huge effect on the phase behavior of ammonium and imidazolium ILs. 

Similar to the imidazolium ILs, very low solubility of the ammonium ILs was observed in alkanes. Eor example, the solubility of butyl(2-hydroxyethyl) dimethylammonium bromide, [(Ci)2C4HOC2N]Br, exhibited a simple eutectic system with immiscibility in the liquid phase in the IL mole fraction range from XjL = 0.02 to 0.70 [53] the other ammonium salt, (benzyl)dimethyl-alkylammonium nitrate, [Be(Ci)2C N] [NOJ showed very small solubility in the liquid phase in hexadecane and it was slightly better in hexane (immiscibility from XjL = 10 to 0.90) [99] for the ammonium salt with an alkane substituent only, didecyldimethylammonium nitrate, [(Cio)2(Q)2N][N03], the solubility in the liquid phase was better in hexane (immiscibility from XjL = 10 to 0.50) than in hexadecane, where the immiscibility was observed in the whole IL mole frachon [100]. In all systems with imidazolium and ammonium salts, an increase in the alkyl chain length of the alkane (solvent) resulted in a decrease of solubility. 

FIGURE 18.4 Phase diagram of a simple eutectic system. AttemperaturesbelowcurveXYorYZ, either solid A [drug] or solid B [carrier] solidi es rstfrom the molten mixture, respectively. At eutectic composition Y both drug and carrier solidify simultaneously as a mixture of nely divided crystalline components. 

Consider a simple eutectic system shown in the following figure. When the melt s is cooled, find... 

FIGURE 10.6 Phase diagram for the simple eutectic system naphthalene-benzene. 

It is a well known phenomenon that metals can significantly influence the crystallization of amorphous Si. The temperature required to crystallize bare a-Si is about 600°C. The contact of a-Si with metals usually leads to a strong reduction of this crystallization temperature (metal-induced crystallization). Metal/Si systems can be divided into (1) compound forming systems, which form stable metal silicide phases in thermodynamic equilibrium (e.g., Ni/Si, Pd/Si, Pt/Si) and (2) simple eutectic systems, which do not form stable... 

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