Liquids liquidus curve

Uquidus curve The freezing point of a molten mixture of substances varies with the composition of the mixture. If the freezing points are plotted as a function of the composition, the line joining the points is called a liquidus curve. Such mixtures usually freeze over a range of temperature. If the temperature at which the last traces of liquid just solidify (assuming that sufficient time has been allowed for equilibrium to be established) are plotted against composition the resulting line is called a solidus curve. 

For the alloy marked 1 , on cooling, the liquidus curve was intercepted at a relatively high temperature and there was a fair temperature interval during which for the Mg crystals it was possible to grow within the remaining part of liquid. The solidification finally ended at the eutectic temperature. At this temperature the eutectic crystallization occurs (L (Mg) + Cu2Mg) in isothermal conditions, where the simultaneous separation of the two solid phases results in a fine mixture... 

The system is strictly binary only for T < 1078 °C. In K-rich compositions at higher T, the sanidine solid mixture (Sa jn.) is metastable with respect to the leucite solid mixture (K, Na)AlSi206 (Le jn.)- On the Na-rich side of the join (Abg jn.) the crystallization trend of an initial liquid mixture of composition Cl (80% Ab by weight) is similar to that of the previous example. On the K-rich side of the join, cooling of an initial composition C2 (50% Ab by weight) leads to initial formation of crystals the residual liquid moves along the liquidus curve until it reaches the peritectic reaction point P (T = 1078 °C). At P, Le jn. converts into while T remains constant. As shown in figure 7.6B, the... 

The immiscibility in the liquid phase was observed for [CjoCilm]Cl with water and for [C8Qlm]Cl wifh water and 1-octanol [51]. For both salts the solubility in 1-octanol was higher than that in water. Only [C8Cilm]Cl was liquid at room temperature (melting point, = 285.4 K) [51]. The binary mixtures of [Ci2Cilm]Cl with n-alkanes and ethers have shown a very flat liquidus curve, but only in [C42Cjlm]Cl + n-dodecane, or methyl 1,1-dimeth-ylether] the immiscibility in the liquid phase was observed for the very low solvent mole fraction [95]. 

The interesting influence of the cation on the SLE diagram IL + water can be observed [99,100] from the diagrams of ammonium salts [(Cio)2(Q)2N][N03] and [Be(Ci)2C N][N03]. Simple liquidus curve and no immiscibility in the liquid phase for the didecyldimethylammonium cation with the eutectic point shifted strongly to the solvent-rich side was noted (see Figure 1.11). 

The general case of two compounds forming a continuous series of solid solutions may now be considered. The components are completely miscible in the solid state and also in the liquid state. Three different types of curves are known. The most important is that in which the freezing points (or melting points) of all mixtures lie between the freezing points (or melting points) of the pure components. The equilibrium diagram is shown in Fig. 1,16, 1. The liquidus curve portrays the composition of the liquid phase in equilibrium with solid, the composition of... 

The dashed lines in (7.90) illustrate an expected cooling path for a liquid chosen to be of initial concentration v = xB — 0.1. As cooling proceeds (1), the first precipitate of solid a appears when the cooling path meets the a-liquidus curve. Thereafter, as solid a proceeds to freeze out of solution, the melt is successively depleted of component A and moves down the a-liquidus curve (2) toward the eutectic point. At this point, the remaining liquid freezes to a mix of solid a and /3 (in proportion to eutectic composition), and the mix of solids... 

The two upper curves, termed the liquidus curve, define the temperatures at which Au-Si alloys begin to solidify. The curves meet at 363°C at an alloy composition containing 18.6 atomic percent Si. At this temperature, all Au-Si alloys, irrespective of composition, complete their solidification by the eutectic separation of a fine mixture of Au and Si from the liquid phase containing 18.5 atomic percent Si. The horizontal line at 363°C is called the solidus because below such a line all of the alloys arc completely solid. 

H. 0. Jones and J. K. Mathews found that when nitrosyl chloride and hydrogen are passed over reduced platinum cooled by a freezing mixture, the ammonium chloride produced contains 5 per cent, of hydroxylamine chloride. W. J. van Heteren found liquid chlorine and liquid nitrosyl chloride are miscible in all proportions. N. Boubnoff and P. A. Guye examined the f.p. of the binary system N0C1-C12, and found that the liquidus curve exhibits no maximum, and there is no sharp minimum at the eutectic temp., —109°, Fig. 99. The bending of the curve near —107° indicates... 

The bottom line of the diagram is called the liquidus curve. This line represents a collection of the melting points of all mixtures and of the pure components A and B. The top line is called the solidus curve and is a collection of all the solidification points of all mixtures and the pure substances A and B. In the L field one liquid phase and in the S field one solid phase occur. In the L + S field a solid and a liquid phase are present. How should such a diagram be read First of all it is important to realise that every point in the diagram represents a system which is characterized by a temperature, com-... 

The saturation concentration is equal to the solubility of a solid in a liquid at a given temperature. Therefore, its value can in principle be found from the liquidus curve of the equilibrium phase diagram of the A-B binary system (see Fig. 1.1). 

Applying pressurized gases for melt crystallization is advantageous due to their enhanced solubility in liquids. Correspondingly the freezing curve (liquidus curve) depends on pressure, sort of gas and melt. In this the effects of inert gases (i.e. N2) are small and similar to static pressure, but those of more soluble gases (i.e. C02) are much more distinct. 

Equation (7) is obtained from Equation (2) by noting that the solid phase is pure, and therefore the mole fraction and activity coefficient in the solid phase are both unity. The ratio of pure-component fugacities can be obtained from any one of Equations ((3) to (6)), and the activity coefficient in the liquid, Ji, must be estimated. The composition-temperature behavior along the liquidus curves may then be calculated. The eutectic point is found from the intersection of the two liquidus curves. 

If the solution is dilute (i.e. the liquidus curve exists over a narrow concentration range near the pure solvent axis), then the activity coefficient of the solute in the liquid solution can be replaced by its value at infinite dilution. Furthermore, a simple relationship may be employed for the temperature-dependence of the infinite-dilution activity coefficient as follows ... 

The liquidus curves can be obtained by solving the thermodynamic relationship already presented above, since pure solid A, pure solid B, or pure solid AB is in equilibrium with a liquid phase in each of the instances described. The fugacity of pure subcooled liquid AB may be obtained by considering the reaction equilibrium in the liquid phase, so that... 

The thermodynamic relationships for equilibrium between a pure solid and a (ternary) liquid solution have already been presented in equation (7). However, the activity coefficient is now a function of the mole fractions of the three components, as well as the temperature. Along the liquidus curve Eg -D, pure B and pure C crystallize as the solution is cooled. We may therefore write... 

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