WHAT IS A PHASE DIAGRAM

A phase diagram is a graphic representation of the phase behavior of a system under study. The behavior of a single component as a function of temperature and pressure can be represented on a phase diagram, which will show the conditions under which a material is a solid, liquid, or gas. More complex phase diagrams may involve several components. Phase diagrams are very useful tools for formulation, as they allow one to define not only the acceptable composition range of a product but also enable one to optimize the order of addition of the different raw materials. 

Metallurgists and ceramicists quite often deal with simple two- and three-component systems and use phase diagrams to represent their experimental 

Phase diagrams represent equilibrium relationships. Once these are depicted, simple processes such as melting and crystallization can be considered, but because as represented on diagrams these involve continuous successions of equilibrium states, they are reversible processes in the sense of 2.6.2. 

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What is a phase diagram What useful information can be obtained from study of a phase diagram ... 

What is a phase diagram Draw a generic phase diagram and label its important features. 

Up to this point, we have considered only one solid at a time. However, when two (2) or more solids are present, they can form quite complicated systems which depend upon the nature of each of the solids involved. To differentiate and to be able to determine the differences between the phases that may arise when two compounds are present (or are made to react together), we use what are termed "phase-diagrams to illustrate the nature of the interactions between two solid phase compositions. You will note that some of this material weis presented earlier in Chapter 1. It is presented here again to further emphasize the importance of phase diagrams. 

A phase diagram is often considered as something which can only be measured directly. For example, if the solubility limit of a phase needs to be known, some physical method such as microscopy would be used to observe the formation of the second phase. However, it can also be argued that if the thermodynamic properties of a system could be properly measured this would also define the solubility limit of the phase. The previous sections have discussed in detail unary, single-phase systems and the quantities which are inherent in that sjrstem, such as enthalpy, activity, entropy, etc. This section will deal with what happens when there are various equilibria between different phases and includes a preliminary description of phase-diagram calculations. 

Most metals of practical importance are actually mixtures of two or more metals. Recall from Section 1.1.3 that these intimate mixtures of metals are called alloys, and when the bond between the metals is partially ionic, they are termed intermetallics. For the purposes of this chapter, and especially this section, we will not need to distinguish between an intermetallic and an alloy, except to note that when a compound is indicated on a phase diagram (e.g., CuAb), it indicates an intermetallic compound. We are concerned only with the thermodynamics that describe the intimate mixing of two species under equilibrium conditions. The factors affecting how two metal atoms mix has already been described in Section 1.1.3. Recall that the solubility of one element in another depends on the relative atomic radii, the electronegativity difference between the two elements, the similarity in crystal structures, and the valencies of the two elements. Thermodynamics does not yet allow us to translate these properties of atoms directly into free energies, but these factors are what contribute to the free energy of... 

Draw a phase diagram of water. What is called a phase, component, and degree of freedom How many phases and degrees of freedom are there at different points of the phase diagram of water What is known as the freezing (boiling) point of pure substances ... 

Using published data, draw a phase diagram of the sodium sulphate-water system. Proceeding from the phase rule, determine which parts of the diagram will characterize invariant, monovariant, and divariant systems. What is meant by the transition point ... 

What is a typical pressure-temperature phase diagram for sH hydrates ... 

The figure shown is the phase diagram of the substance A. P is the vapour pressure of A in equilibrium with the liquid A at the temperature 7 ,. Pa indicates the ambient pressure. If the temperature is raised to Tb, what would happen to the liquid ... 

The following is the phase diagram of sulphur. The stable form of sulphur at ordinaiy temperature is a sulphur which has a rhombic crystal structure. At what temperature will rhombic sulphur melt upon slow heating If the sulphur is heated rapidly, at what temperature will it melt ... 

For a polymer blend, where both mA and mB may be 1000, the critical value of x will be very small, Keep in mind what this means. Any value of x that is larger than means that the system will phase-separate at some composition. This is perhaps more easily seen if you recall that x varies approximately as 1/T, and a phase diagram can therefore be plotted as 1/x versus composition, if we so choose (Figure 11-22). Note also that the shape of the binodal and spinodal curves will depend upon the relative size of the molecules and will be skewed to one side or the other if mA is not equal to mB. 

C is correct. This is just a phase diagram with pressure on a log scale. There are many ways to manipulate the phase diagram. Don t be intimidated. Try to compare it to what you know. 

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