NaCl phase diagram

C. Telang, R. Suryanarayanan and L. Yu, Crystallization of D-mannitol in binary mixtures with NaCl phase diagram and polymorphism, Pharm. Res., 2003, 20, 1939-1945. 

Concept Check 9.6 The following is a portion of the H20-NaCl phase diagram ... 

Potassium Heptafluorotantalate. Potassium heptafluoiotantalate [16924-00-8], K TaF, ciystallizes in colodess, rhombic needles. It hydroly2es in Foiling water containing no excess of hydrofluoric acid. The solubility of potassium heptafluorotantalate in hydrofluoric acid decreases from 60 g/100 mL at 100°C to 0.5 g/100 mL at room temperature. The different solubility characteristics of K TaF and K NbOF are the fundamental basis of the Matignac process (16). A phase diagram exists for the system K TaF —NaCl—NaF—KCl (68). Potassium heptafluorotantalate has an LD q value of 2500 mg/kg. The recommended TWA maximum work lace exposure for K TaF in air is 2.5 mg /m (fluoride base) (69). 

Figure 18. Phase diagram of the NaCl - NiCI2 system. The stipled area is the operating region of the ZEBRA cell.

Present production processes use two stage counter-current extraction to remove americium from molten plutonium with magnesium chloride based salts. Both 35 mole % NaCl - 35 mole % KC1 - 3D mole % MgCl2 and 50 mole % NaCl-26 mole % CaCl2 - 24 mole % Mg Cl 2 are used for americium extraction. Figures 4 and 5 show the ternary phase diagrams for these salt systemsU0). 

Figure 5. Ternary Phase Diagram for the NaCl-CaCl2-MgCl2 System.

The changes in osmotic coefficients with temperature and concentration make it difficult to solve the above equations accurately, but accurate determinations of the composition and relative amounts of the concentrated liquid and ice can be made from phase diagrams which are plots of the freezing points of solutions versus their concentration. From these, it is possible to determine the exact NaCl concentration at any temperature. Examples are shown in Figure 9 for solutions of 0 to 2.0 M glycerol in 0.15 M NaCl. This figure nicely illustrates how the presence of glycerol reduces the concentration of NaCl in the residual unfrozen solution. 

FIG. 1 Partial phase diagram of brine, decane, and AOT system as a function of temperature (T) and decane-to-brine weight fraction (a). The brine is aqueous 0.6% (w/w) NaCl the AOT composition is constant at 12% (w/w). The double-ended arrow depicts the isothermal composition range examined in this study at 45°C. The lamellar (L ), and two-phase regions (2,2) are described in the text. (Adapted from Fig. 5 of Ref. 20.)... 

Fig. 1. Phase diagram for the AlCl3-NaCl molten salt. Reproduced from Fannin et al. [32] by permission of the American Chemical Society, Inc.

The phase distribution observed in the alloys deposited from AlCb-NaCl is very similar to that of Mn-Al alloys electrodeposited from the same chloroaluminate melt [126 129], Such similarity may also be found between the phase structure of Cr-Al and Mn-Al alloys produced by rapid solidification from the liquid [7, 124], These observations are coincident with the resemblance of the phase diagrams for Cr-Al and Mn-Al, which contain several intermetallic compounds with narrow compositional ranges [20], inhibition of the nucleation and growth of ordered, often low symmetry, intermetallic structures is commonly observed in non-equilibrium processing. Phase evolution is the result of a balance between the interface velocity and... 

Fig. 2.19. A phase diagram of orientational states for adsorbed molecules on a square lattice. Phase-separating solid and dash-dotted lines correspond to the case Ki = 0. The dotted line enclosed by the markers x specifies parameters of the system CO/NaCl(100) (K /Ki = 0.207, 0= 25°)...

Figure 4.7 (a) Phase diagram of the system KCl-NaCl. (b) Gibbs energy curves for the solid and liquid solutions KCl-NaCl at 1002 K. Thermodynamic data are taken from reference [5]. 

Boryak, O.A. Stepanov, I.O. Kosevich, M.V. Shelkovsky, V.S. Orlov, V.V. Blagoy, Y.P. Origin of Qnsters. I. Correlation of Low Temperature FAB Mass Spectra With the Phase Diagram of NaCl-Water Solutions. Eur. Mass Spectrom. 1996,2,329-339. 

Lithium hydride, LiH, decomposes (under appropriate conditions of temperature and pressure) to solid Li and gaseous H2. Solid Li is a bcc crystal, while LiH has the NaCl structure. Constmct an ab initio phase diagram for LiH and Li as a function of temperature and H2 pressure. 

Ferrous oxide is known as wustite (FeO), and it has the NaCl (rock salt) crystal structure. Accurate chemical analysis demonstrates that it is non-stoichiometric it is always deficient in iron. The FeO phase diagram (Figure 5.25) illustrates that the compositional range of wustite increases with temperature and that stoichiometric FeO is not included in the range of stability. Below 570 "C, wustite disproportionates to a-iron and Fe304. 

Figure 3.3 Illustration of the calculation of the phase diagram of a mixed biopolymer solution from the experimentally determined osmotic second virial coefficients. The phase diagram of the ternary system glycinin + pectinate + water (pH = 8.0, 0.3 mol/dm3 NaCl, 0.01 mol/dm3 mercaptoethanol, 25 °C) —, experimental binodal curve —, calculated spinodal curve O, experimental critical point A, calculated critical point O—O, binodal tielines AD, rectilinear diameter,, the threshold of phase separation (defined as the point on the binodal curve corresponding to minimal total concentration of biopolymer components). Reproduced from Semenova et al. (1990) with permission.

Historically, however, it has been much more common for experimentalists to introduce a new variable into Figure 1, changing either the temperature of one or more samples of fixed composition, or the electrolyte concentration in a series of samples of fixed amphiphile—oil—water ratio. The former constitutes a temperature scan the latter experiment is widely known as a salinity scan. When the temperature of an amphiphile—oil—water system is varied, the phase diagram can be plotted as a triangular prism (because temperature is an intensive or field variable). When a fourth component (eg, NaCl) is added at constant temperature, tetrahedral coordinates, are appropriate (conjugate phases have different salinities, and the planes of different tietriangles are no longer parallel). 

Figure 4. Phase Diagram for diesel (EACN=13.3) at 22°C for 2.0% AOT, 2.0% Tween 80, and NaCl.

Figure 5. Phase Diagram for hexadeeane (EACN=16) at 22°C for 2% AOT, 2% Tween 80, and NaCl. The open circles are data. The closed squares represent the phase diagram for a surfactant system which progresses through types ]4=>IIle II with neither phase separation nor precipitation.

Urusova MA, Valyashko VM. Tricritical phenomena in the NaCl-Na2B407-H20 system and the transformation laws of complete phase diagrams. Russ J Inorg Chem 1998 43 948-955. 

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