Water-salt eutectics

The found regularities are explained in view of features of crystallization of ice, mechanism of entrance of impurity in a solid phase during LTDC of water solutions, and of dependence of stmcture of a water-salt eutectic by nature of salt-macrocomponent. 

Range of water/salt eutectics Oto-64 Wider range Wide range... 

Transition Region Considerations. The conductance of a binary system can be approached from the values of conductivity of the pure electrolyte one follows the variation of conductance as one adds water or other second component to the pure electrolyte. The same approach is useful for other electrochemical properties as well the e.m. f. and the anodic behaviour of light, active metals, for instance. The structure of water in this "transition region" (TR), and therefore its reactions, can be expected to be quite different from its structure and reactions, in dilute aqueous solutions. (The same is true in relation to other non-conducting solvents.) The molecular structure of any liquid can be assumed to be close to that of the crystals from which it is derived. The narrower is the temperature gap between the liquid and the solidus curve, the closer are the structures of liquid and solid. In the composition regions between the pure water and a eutectic point the structure of the liquid is basically like that of water between eutectic and the pure salt or its hydrates the structure is basically that of these compounds. At the eutectic point, the conductance-isotherm runs through a maximum and the viscosity-isotherm breaks. Examples are shown in (125). 

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). 

LI Eutectic phase relations in water-salt systems These systems usually involve... 

Eutectic formation, as predicted by the phase rule, can have a dramatic effect on pH buffer solutions during freezing. In a ternary solution of two salts and water, four eutectic points may, in principle, be identified, of which one is a ternary eutectic (at the lowest temperature), while the other three are binary eutectics of the three pairs of components. Some eutectic data for sodium and potassium phosphate buffer salts with ice are summarised in Table For mixtures of the sodium salts, the... 

Many binary systems, both ideal and nonideal, have phase diagrams of the simple eutectic type. The phase diagram, water-salt, is the simple eutectic type if the salt does not form a stable hydrate. The diagram for H20-NaCl is shown in Fig. 15.10. The curve ae is the freezing-point curve for water, while efis the solubility curve, or the freezing-point curve, for sodium chloride. 

In the open-cycle externally cooled, two-fluid LMFR, the bismuth-uranium solution serves as the primary coolant as well as the fuel. In the reactor itself, there is no actual heat transfer. Instead, the solution acts as a transporter of heat to an external heat exchanger. In evaluating bismuth as a primary coolant, it is helpful to make a comparison between it and three other coolants sodium, a typical alkali metal coolant LiCl-KCl eutectic, a typical alkali halide salt mixture and water. (The salt eutectic used here would not be a suitable primary coolant for a thermal reactor. Its heat transfer properties, however, are typical of salt coolants.)... 

The reaction is exothermic, and multitubular reactors are employed with indirect cooling of the reactor via a heat transfer medium. A number of heat transfer media have been proposed to carry out the reactor cooling, such as hot oil circuits, water, sulfur, mercury, etc. However, the favored heat transfer medium is usually a molten heat transfer salt which is a eutectic mixture of sodium-potassium nitrate-nitrite. 

Hitec Heat-Transfer Salt. Hitec heat-transfer salt, manufactured by Coastal Chemical Co., is an eutectic mixture of water-soluble inorganic salts potassium nitrate (53%), sodium nitrite (40%), and sodium nitrate (7%). It is suitable for Hquid-phase heat transfer at temperatures of 150—540°C. 

Salt Brines The typical curve of freezing point is shown in Fig. II-IIO. Brine of concentration x (water concentration is I-x) will not solidify at 0°C (freezing temperature for water, point A). When the temperature drops to B, the first ciystal of ice is formed. As the temperature decreases to C, ice ciystals continue to form and their mixture with the brine solution forms the slush. At the point C there will be part ice in the mixture /(/i+L), and liquid (brine) /i/(/i-t-L). At point D there is mixture of mi parts eutectic brine solution Di [concentration mi/(mi-t-mg)], and mo parts of ice [concentration mol m -t- mo)]. Coohng the mixture below D solidifies the entire solution at the eutectic temperature. Eutectic temperature is the lowest temperature that can be reached with no solidification. 

The LCM baths use a mixture of nitrate/nitrite eutectic salts. As it contains up to 40% sodium nitrite the salt system is toxic and can cause water pollution, and also cause nitrosation of volatile secondary amines. 

Sodium chloride is found in salt beds, salt brines, and sea water throughout the world, and it is also mined is some locations. Consequently, sodium chloride is the source of numerous other sodium compounds. A large portion of the sodium chloride utilized is consumed in the production of sodium hydroxide (Eq. (11.23)). The production of sodium metal involves the electrolysis of the molten chloride, usually in the form of a eutectic mixture with calcium chloride. Sodium carbonate is an important material that is used in many ways such as making glass. It was formerly produced from NaCl by means of the Solvay process, in which the overall reaction is... 

Eutectic point (Tc) A single point on a temperature concentration phase (or state) diagram for a binary solution (e.g., water and sugars or salts) where the solution can exist in equilibrium with both crystalline solute and crystalline solvent. Under equilibrium conditions, cooling at Te results in simultaneous crystallization of solvent and solute in constant proportion and at constant temperature until maximum solidification has occurred (based on Fennema, 1996). 

However, there are no known SB systems with Mg in aqueous solutions. The Mg anode s irreversibility in aqueous solutions is thought to be due, in part to the existence of monovalent Mg ions during the electrochemical discharge, in part to the selfcorrosion and film formation, and in part caused by other factors (136,140). All attempts to deposit this metal on the negative electrode from aqueous electrolytes have failed. It is claimed that the Mg cell with molten salt electrolyte, LiCl-KCl eut., is reversible (141) it operates at temperatures above the eutectic melting point, i.e. about 400°C. Small amounts of water might decrease the operating temperature. 

Klochko, M.A., "On the Interrelation Between the Compositions of Conductance Maxima and of the Eutectic Point in Salt-Water Systems", Doklady, Adad. SSSR, 82, 261 (1952). 

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