Liquidus boundaries

Kushiro 1. (1975) On the nature of silicate melt and its significance in magma genesis regularities in the shift of the liquidus boundaries involving olivine, pyroxene, and silica minerals. Am. J. Sci. 275, 411-431. 

Analogous phase behavior has been observed at the liquidus boundary of the DOACS water system. (DOACS is dioctadecylammonium cumenesulfo-nate, a thermally stable surfactant that also exists as a thermotropic lamellar liquid crystal phase at temperatures above its crystal phase.) A phase study of this system revealed that the temperature of this liquidus also increases as water is added [26]. Water would be expected to stabilize C12MG, provided no hydrolytic cleavage reactions (such as amide hydrolysis) occur [27], No... 

Five phases were found to exist between 25 °C and 130°C in the equilibrium Ci2MG-water system a crystal phase (XI), a liquid phase (to the dilute side of the diagram), and three liquid crystal phases (lamellar, cubic, and hexagonal, in order of decreasing surfactant composition). The liquid phase is contiguous with the water border, and the liquidus boundary has a classical form. The plateau region of the Krafft boundary also has a familiar form, except that it displays an unusually shallow slope [33]. This feature is important with respect to the interpretation of DSC data. 

There are insufficient data available at present to allow more extensive tests of the model on other systems. However by combining this model with the acid-base scale described above, the shifts in liquidus boundaries noted by Kushiro (1973, 1975) can be interpreted. 

For example, consider again the 35 wt% Ni-65 wt% Cu alloy at 1250°C, located at point B in Figure 9.3b and lying within the a -H L region. Thus, the problem is to determine the composition (in wt% Ni and Cu) for both the a and liquid phases. The tie line is constructed across the a -I- L phase region, as shown in Figure 9.3b. The perpendicular from the intersection of the tie line with the liquidus boundary meets the composition axis at 31.5 wt% Ni-68.5 wt% Cu, which is the composition of the liquid phase, Likewise, for the solidus-tie line intersection, we find a composition for the a solid-solution phase, Cq, of 42.5 wt% Ni-57.5 wt% Cu. 

DEF. The phase boundary which limits the bottom of the liquid field is called the liquidus line. The other boundary of the two-phase liquid-solid field is called the solidus line. 

In these phase diagrams, the liquidus line represents the temperature at which one of the components crystallizes, while, below the solidus line, the whole system solidifies. Between the solidus and liquidus lines are the regions where solid and liquid coexist. Since there is no solid phase above the liquidus lines and the liquid is thermodynamically stable. Ding et al. suggested that the liquidus temperatures should be adopted as the lower boundary of the liquid phase, instead of the solidus temperatures. The patterns of these phase diagrams are... 

Figure 4.5 shows the liquidus and solidus for In-Pb determined during cooling from the liquid the solidus, in this case, is a non-equilibrium boundary. This was demonstrated by Evans and Prince (1978) when they atmealed as solidified alloys for several hours just below their measured solidus. On re-heating melting occurred at a higher temperature than had been measured by DTA. The samples were then annealed for several hours just below the new measured melting temperature before being heated until melting was just observed again. The cycle was repeated until the solidus temperature became reproducible and the temperature then plotted as the true solidus. This is compared with the apparent solidus on the initial cooling experiment in Fig. 4.5. This paper shows the problems that can occur with...

Again, providing the various H and S terms are temperature-independent, the solution remains exact and provides a rapid method of calculating the liquidus temperature. Equation (9.10) is generally applicable to any phase boundary between a solution phase and stoichiometric compound, so could equally well be used for solid-state solvus lines. 

So, for this binary solution of components A and B, which mix perfectly at all compositions, there is a two-phase region at which both solid and liquid phases can coexist. The uppermost boundary between the liquid and liquid + solid phase regions in Figure 2.3f is known as the liquidus, or the point at which solid first begins to form when a melt of constant composition is cooled under equilibrium conditions. Similarly, the lower phase boundary between the solid and liquid + solid phase regions is known as the solidus, or the point at which solidification is complete upon further equilibrium cooling at a fixed composition. 

These lines are called liquidus isotherms. The intersections of adjoining liquidus surfaces like ae, be and ce are called the boundary curves. When a liquid whose composition lies in the region surrounded by Aceh is cooled, the first crystalline phase that appears is A, and hence A is called the primary phase and the region Aceh is the primary field of A. In this field, solid A is the last solid to disappear when any composition within this field is heated. Similarly,B and C are primary phases in their respective primary fields, Baec and Caeb. 

The preceding information may be assembled into an equilibrium phase diagram shown in part (f), which is typical for this type of system. The diagram shows the T-x regions in which the homogeneous solid or liquid is stable the two corresponding boundary lines are known as the solidus and liquidus the T-x... 

The primary phase fields that appear on the liquidus surface within the K20-Al203-Si02 system are shown in Fig. 6 [20]. The field of cristo-balite extends from 1470 10°C, the temperature of the boundary curve between cristobalite and tridymite to the melting point of cristobalite at 1713 + 5°C. 

As previously discussed, both potassium tetrasilicate and potassium disilicate melt congruently at 770 2°C and 1045 2°C, respectively. Both compounds crystallize readily from appropriate melts when no potash feldspar crystals are present. In the region of the boundary curve between the tetrasilicate field and potash feldspar field, it is possible to follow the metastable extension of the potassium tetrasilicate liquidus surface beneath the stable potash feldspar field. Near the boundary curve between the disilicate field and the potash feldspar field, a metastable extension of the disilicate liquidus surface beneath the stable potash feldspar field is also possible providing once again that no potash feldspar crystals are present. 

Thermochemical properties of numerous different condensed phases were determined from the gas phase data as shown in the preceding section. In addition phase boundaries were also evaluated thereby improving our knowledge of phase diagrams. The liquidus line determined by Timberg and Toguri... 

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