Trends in mutual liquid solubilities

All the phase diagrams reported above show a complete mutual solubility in the liquid state. The formation of a single phase in the liquid state corresponds to behaviour frequently observed in intermetallic (binary and complex) systems. Examples, however, of a degree of immiscibility in the liquid state are also found in selected intermetallic systems. Fig. 2.16 shows a few binary systems in which such immiscibility can be observed (existence of miscibility gaps in the liquid state). All the three 

The diagram Na-Al in Fig. 2.16(c) corresponds to extremely small solubilities the solubility of Na in Al has been evaluated in less than 0.002 at.%, while that of Al in Na is practically zero. 

A summary of all the metal pairs showing partial or complete immiscibility in the liquid state is presented in the map of Fig. 2.17. In the same figure metal pairs giving solid-gas equilibria are also shown. The solid-gas equilibria are especially observed in systems in which there is a large difference in the boiling points of the components (see for instance the systems formed by the alkali metals with refractory metals such as Cr, Mo, V etc.). Several groups of systems forming miscibility 

The Te-S system is peculiar it is a simple eutectic-type diagram and shows (like an island completely surrounded by the single-phase field of the liquid) a small oval insolubility region situated between —37 and 41.5 at.% S and between two critical temperatures (upper Tc = 740°C and lower Tc = 690°C). This behaviour (often observed for instance in organic systems) among the different pairs of elements has been described only for Te-S. 

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