Vapour species diagrams

Vapour-species diagrams which allow the vapour pressures of compounds to be presented as a function of convenient variables such as partial pressure of a gaseous component. 

The use of the various vapour species and stability diagrams requires the knowledge of the reactive components in the gas phase. The following sample calculation illustrates how this can be accomplished in a simple case. 

Schick s work includes the study of borides, carbides, nitrides, and oxides of some elements in Groups IIA, IIIB, IVA, IVB, VB, VIIB, and VIII as well as selected rare earths and actinides. As far as possible, the tables have been made compatible with the JANAF tables. Among the subjects treated are phase diagrams, heat capacities, enthalpies, entropies, enthalpies of phase transformation, formation, and reaction, melting temperatures, triple points, free energies of formation, vapour pressures, compositions of vapour species, ionization and appearance potentials, e.m.f. of cells, and enthalpies of solution and dilution. Volume 1 summarizes the techniques used to analyse data and cites the data analysed, and Volume 2 gives tables of values produced by this study. 

Figure 5.1 presents the behaviour of a pure species that can exist as solid, liquid or vapour in a pressure-temperature diagram. We may have three types of two-phase equilibrium solid/liquid, vapour/liquid and solid/vapour. There is a point where all three phases coexist, designated by the triple point. Here the phase rule gives F=C+2-P= +2-3=Q degrees of freedom. Neither pressure nor temperature can be used to modify the equilibrium. If only two phases can be found at equilibrium F=l+2-2=l, and either pressure or temperature can vary. The most important equilibrium in process engineering is vapour-liquid equilibrium, abbreviate as VLE. It may be observed that the two phases will coexist up to a point where it is difficult to make a distinction between vapour and liquid. This is the critical point, a fundamental physical property characterised by critical parameters and. Above the critical point the state... 

Prototypical pure substances occur in at least one solid phase, a liquid phase, and a vapour (gas) phase and can be defined/identified in terms of their one-component-phase diagram, triple point(s) connecting the phases. Intermediate substances can be identified by their location in phase diagrams. Substances that seem to occur in only one phase or which cannot be put into bottles for one reason or another can be situated relative to protot3q>ical substances. Different research contexts may lead to different classifications of non-standard cases, but often a distinction of component, substance, and species will resolve some ambiguities. 

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