Eutectic diagrams

The above thermodynamic information gives an idea about the maximum amount of material that will crystallize as a solid however, to get an insight into the rate of the prodnction of crystals we need information about its kinetics. The crystallization kinetics provide design information like crystal production rate, size distribution, and its shape. 

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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. 

The phase diagram of a binary system as shown below is effectively two simple eutectic diagrams linked together. Therefore there are two eutectic points in this kind of the system. A maximum point appears on the liquidus, which is the melting point of the congruently-melting compound. 

Fig. 18. Ternary eutectic diagram in the AljOj-YjOj-MgO system. After Bosomworth et al. [10],...

Generally, water freezes from an aqueous solution. A phase diagram (temperature versus composition) then gives the phase transitions that will occur, assuming equilibrium. Most solutes give a eutectic diagram characterized by a eutectic temperature (7).) and solute concentration (ij/e). Below ij/e, water will freeze upon cooling, and the solution becomes more... 

Eutectic Diagrams with Partial Solid Solubility and No Intermediate Compounds... 

SOLID-LIQUID EQUILIBRIA THE SIMPLE EUTECTIC DIAGRAM... 

It is conceivable that more than one compound is f ormed between the two substances this is often the case with salts and water. The salt forms several hydrates. An extreme example of this behavior is shown by the system ferric chloride-water Fig. 15.12. This diagram could be split into five simple eutectic diagrams. 

An example of the use of a ternary eutectic diagram for the assessment of a melt recrystallization process (for nitrotoluene isomers) is given in section 8.2.1. 

This analysis would not likely apply at the temperatures of the knee or plateau regions, as the dependence of activities on concentration is greatly complicated by the existence of micellar phenomena. Because no ternary aqueous surfactant phase study has been performed to date at a temperature below the Krafft eutectic of the binary aqueous surfactant system, little information exists regarding the influence of a third component on the crystal solubility of surfactants (except for the influence of added salts, as described above). It has been shown that plane sections through ternary diagrams of two surfactants and water have an appearance similar to the familiar eutectic diagram found in numerous nonsurfactant binary systems [45]. 

Sometimes, two substances A and B combine to form a compound corresponding to a stoichiometric compositional formula such as AB or AB2, etc. The melting point curve then takes the form of two or more simple eutectic diagrams juxtaposed at the point on the composition axis corresponding to the compositional formulas AB, AB2, etc. of the compounds. The curve has a maximum at these points on the composition axis, which is the melting point of the pure compound a composition corresponding to a mixture of the compound with one or more of its components would have a lower melting point. 

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