Eutectic phase formation

R A. Monnard et al. from the laboratory of D. W. Deamer also worked on ice/eutectic phases at 255 K. They studied the influence of solutions of inorganic ions (such as Na+, CD, Mg2+, Ca2+ and Fe2+) both on the formation of vesicles and on non-enzymatic polymerization of activated RNA monomers (Monnard et al., 2002). 

It is also interesting to note that electroless plating of silver on carbon fiber surface improves the wettability between molten aluminum and PAN based carbon fibers using the liquid infiltration technique in vacuum (Warrier et al., 1993). This is attributed to the formation of an eutectic phase between silver and aluminum, and the silver coating of the fibers during processing. 

Figure 4. Section of the pseudobinary phase diagram of the sulfuric acid SLP catalytic material. The data were taken from Ref. 16. The data points were derived from anomalies of the conductivity versus temperature curves of the respective mixtures. At the high compositional resolution and in the range of the global eutectic, the formation of a vanadate-sulfato complex causes the local maximum in the solidus curve. It is noted that extreme precision in the experimental procedures was necessary to derive this result illustrating the characteristic of fused systems that compound formation can well occur in the molten state.

Industrially, milk fat is commonly added to cocoa butter to produce milk chocolate. However, there is a thermodynamic incompatibihty between the miUc fat and cocoa butter solids which results in eutectic phase behavior. This eutectic formation leads to a chocolate with a decreased hardness (Timms 1980 Bama et al. 1992 Bystrom and Hartel 1994 Reddy et al. 1996). Extensive work has been carried out on the addition of milk fat to cocoa butter because of its abihty to reduce the incidence of bloom formation in chocolate (Hartel 1996 Kleinert 1961 Dimick et al. 1993). Chocolate bloom is evident as a white-gray layer on top of the chocolate surface and eventually the chocolate will acquire a crumbly texture. 

Both lead (Pb ) and some lead minerals catalyze the formation of up to 10 mers starting from the 5 -phosphorimidazolide of adenosine (5 -ImpA). 21, 22) The oligomers are linked mainly by 2 , 5 -phosphodiester bonds. Uranyl ion (U02 ) is a more efficient catalyst of the reaction of the activated nucleotides of A, U, and C. (23) Chain lengths 16, 10, and 10 monomer units (mers), respectively are formed that are linked mainly by 2 5 -phosphodiester bonds. When the Pb reaction is performed in the eutectic phase of water at -18° C for... 

In subsequent paper. Senna et al. employed thymol as an efficient additive and showed that formation of eutectic complex facilitates Diels-Alder reaction in mechanical mill (Scheme 5.4) [5]. It was reasoned that formation of eutectic phase via charge-transfer complex leads to better fusion of two reactants and hence increases reaction rate. An equimolar mixture of 9,10-dimethylanthracene 10 and p-benzoquinone 8 with catalytic amount (10 mol%) of thymol 11 were mechanically milled in a closed agate mortar with a single vibrating agate ball to obtain Diels-Alder product 12 in high yield. 

The effect of a second component in the phase structure is treated in this chapter in several stages. First, it was assumed that both components were of identical size and behaved ideally, i.e., they do not interact. Assuming further that there is no cocrystallization, the typical eutectic phase diagram of Fig. 2.27 results. The discussion of the experimental evaluation of phase diagrams indicated the effect of formation of solid solutions, as seen in Fig. 7.2. The deviation from an ideal solution can be treated by introduction of an activity as in Fig. 7.3. Next, in Sect. 7.1.2 the shape-difference of two components was treated using the free-volume argument of Hildebrandt, and finally, the interaction parameter % was introduced to treat real solutions in Fig. 7.4-6. The examples treated in Sects. 7.1.3-5 dealt then with components that were isolated molecules. 

Three limiting theories are outlined next. The first is an equilibrium theory of the eutectic phase diagram of copolymers as developed by Hory which has been widely used, even for systems not in equilibrium. The second is the corresponding theory for the formation of solid solutions. The third is the application of cold crystallization to copolymers as a limiting, nonequilibrium theory of melting and crystallization. 

If the interfacial energy between the a and P phases is low compared to the liquid-a and liquid- interfacial energies, then the a and P phases will prefer to wet each rather than the liquid. As shown in Figure 6.36b, this can lead to the coordinated growth of long alternating lamellar or plateletlike formations of the a and P phases. Such lamellar microstmctures commonly occur for rapidly solidified eutectic phase transformations where insufficient time is provided to approach a more equilibrium microstructure. 

Upon mixing of the two colourless co-crystal constituents in the solid state, the formation of a yellow co-crystal phase is rapidly (within 1 min) observed at the interface of the two solids. Microscopic observation of the interface between two macroscopic single crystals of diphenylamine and benzophenone revealed melting of the surface which proceeds until most of the material is converted to a liquid at room temperature. Subsequent nucleation of the co-crystal phase results in the solidification of the entire melt to form the solid co-crystal. Consequently, the role of grinding in a eutectic-mediated cocrystallization is most likely two-fold first, it provides agitation to expose fresh reactant surfaces for eutectic formation and second, it enhances cocrystal formation by inducing co-crystal nucleation in the eutectic phase (Figure 8.13(c)). 

Fig. 1. Hypothetical To curves for a binary eutectic A-B system (a) To curves drop to low temperature glass formation is possible, (b) To curves intersect at low temperature pertitionless crystalline phase formation occurs (redrawn from Boettinger Perepezko, 1993).

The potential compatibility concerns of bismuth (Bi) containing solder alloys and tin-lead component terminations (or tin-lead solder alloys and bismuth containing component terminations), due to the formation of the low melting temperature (98 °C, or 208 °F) Sn-Pb-Bi ternary eutectic phase, have often been discussed in the literature however, the exact concentration of bismuth necessary to cause an actual reliability degradation (based on kinetics considerations) is not yet clear, and component terminations with tin iloys with low bismuth (1-3%) have been used with the tin-lead solder in actual products. As will be discussed later, bismuth is often used as an alloy addition to tin to reduce the risk of tin whisker growth. 

Let us now examine the formation of the microstructure of eutectic systems of various compositions. First consider the case where the starting composition Co intersects the solvus line between the a phase and the a + p region in the generic eutectic phase diagram shown in Figure 12.19. Once the temperature falls below the solidus line between a and a + L, the solid is a with average composition Cq. When the temperature falls below the solvus line, the a phase becomes supersaturated and small (3 particles will begin to... 

Schaefer, Matt Laub, Werner Foumelle, R.A. Liang, J. Evaluation of intermetaUic phase formation and concurrent dissolution of intermetallic during reflow soldering. Design and Reliability of Solders and Solder interconnections. The Minerals, Metals and Materials Society, 1997 247-257. Liu, A.A. Kim, H.K. Tu, K.N. Totta, P.A. Spalling of CugSns spheroids in the soldering reaction of eutectic SnPb on Cr/Cu/Au thin films. J. Appl. Phys. 1996, 80, 2774. 

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