Liquidus curves

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. 

Fig. 3. The viscosity and liquidus curves for molten sodium silicates, where the numbers on the dashed lines ate viscosity ia Pa-s (1).

The binary system lead-thallium shows an unusual type of phase diagram. Fig. 1, taken from Hansen (1936), represents in the main the results obtained by Kumakow Pushin (1907) and by Lewkonja (1907). The liquidus curve in the wide solid-solution region has a maximum at about 63 atomic percent thallium. The nature of this maximum has not previously been made clear. 

MOLTEN SODIUM SILICATES, VISCOSITY AND LIQUIDUS CURVES... 

Molten sodium silicates, viscosity and liquidus curves for, 22 462 Molten sulfur, handling, 23 771 Molten tin, 24 786 silicon and, 22 489... 

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... 

Figure 2.40. Phase diagram of the Mg-Cu alloy system. For the alloys marked (1) (at 5 at.% Cu) and (2) (at 20 at.% Cu), the DTA curves are shown on the right. Notice that, on cooling, a sharp thermal effect due to the invariant eutectic transformation is observed. At higher temperature the crossing of the liquidus curves is detected. (The coordinates of the eutectic point are 485°C and 14.5 at.% Cu.)...

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... 

Figure 7.9A shows the NaAlSi04-Si02 (nepheline-silica) system, after Schairer and Bowen (1956). Let us first examine the Si02-rich side of the join. At P = 1 bar, the pure component Si02 crystallizes in the cristobalite form (Cr) at r = 1713 °C (cf figure 2.6). At P = 1470 °C, there is a phase transition to tridymite (Tr), which does not appreciably affect the form of the liquidus curve, which reaches the eutectic point at P = 1062 °C. 

Figure 1. Melting point diagrams for the three types of enantiomer systems (only the liquidus curves are shown).

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). 

Figure 1.12 Influence of pressure on the liquidus curve of [CjCjIm][CjS04] (1) + 1-hexanol (2) up to 360 MPa (Adapted from Domariska, U. and Morawski, R, Green Chem., 9, 361, 2007.) experimental points (O), solid line, description with the Yang equation. (Adapted from Yang, M. et al.. Fluid Phase Equilib., 204, 55, 2003.)...

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... 

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