Solidus 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. 

We have found it possible to formulate a simple treatment of the lead-thallium alloys that accounts satisfactorily for the existence of a maximum in melting-point displaced from the composition PbTls of the ordered structure, and that also accounts in a reasonably satisfactory way for the shapes of the liquidus and solidus curves throughout the range 0—75 atomic percent thallium (Fig. 1). The maximum in these curves occurs at a composition near that for a compound Pb2Tl3 or a compound PbTl2. If either of these compounds existed, it would have to be considered as forming solid solutions with lead and with thallium. The data, however, give no evidence for the existence of such compounds. 

Fig. 7. The free-energy curves and the derivation of the liquidus and solidus curves.

The liquid fraction sensitivity is an important parameter for the determination of the semi-solid forming capability. It is defined as the rate of change of the liquid fraction in the alloy with temperature and is related to the relative slopes, in the phase diagram, of the liquidus and solidus curves. It may be determined by differential scanning calorimetry or predicted by thermodynamic modelling. Examples related to various Al alloys have been reported by Maciel Camacho et al. (2003), Dong (2003). See also several papers in Chiarmetta and Rosso (2000). 

Figure 5.24 Phase stability relations for end-members of pyroxene quadrilateral. Melting curves refer to anhydrous conditions. Solidus curves for CaMgSi206 in saturated vapor phase conditions are also shown for various CO2/H2O ratios in the vapor phase. Dashed lines are extrapolated. From Lindsley (1982). Reprinted with permission of The Mineral-ogical Society of America.

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). 

I believe that Dr. Mathot has raised the question of phase equilibration in our phase diagrams. If we consider a simple solid solution, fluid solution phase diagram for a binary mixture, there are two limiting consequences of lowering the temperature from above the fluidus curve (Tj) to below the solidus curve (T2). The solid phase may or may not have... 

It is also assumed that the composition of the grown crystal does not change in the cooling process. As is well known for the case of finite quantity of melt, the composition of melt (liquid) and solid change along the liquidus and solidus curves, respectively. 

SOLIDUS CURVE. A curve representing the equilibrium between the solid phase and the liquid phase m a condensed system of two components. The relationship is reduced to a two-dimensional curve by disregarding the influence, of the vapor phase. The points on the solidus curve are obtained by plotting the temperature at which the last of the liquid phase solidifies, against the composition, usually in terms of the percentage composition of one of the two components. 

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-... 

Figure 4. Section of the pseudobinary phase diagram of the sulfuric acid SLP catalytic material. The data were taken from Ref. 16. The data points were derived from anomalies of the conductivity versus temperature curves of the respective mixtures. At the high compositional resolution and in the range of the global eutectic, the formation of a vanadate-sulfato complex causes the local maximum in the solidus curve. It is noted that extreme precision in the experimental procedures was necessary to derive this result illustrating the characteristic of fused systems that compound formation can well occur in the molten state.

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