Binary systems containing intermediate compounds

Gehlenite is the single intermediate phase in this system. None of the phases has any composition range, unlike the alloys described above, and such compounds are often called line phases. 

The phase diagram shows that gehlenite melts without any changes occurring. This feature is 

Not all intermediate compoimds show congruent melting. Many intermediate compoimds transform into a liquid at a peritectic point. On heating through a peritectic point, a solid transforms to a 

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FIOURE 16.42 E hase diagram for the binary system La203-Nb205, containing four congruently melting intermediate compounds [114]. 

The binary tungsten-carbon system (Fig. 4.1) [4.13-4.15] is of high technical importance. It contains three intermediate compounds W2C(P), WCi ((y), and WC(5), the latter being the main constituent in most of the commercial cemented carbides (hardmetals see Chapter 9). Besides, ternary and even more complex compoimds exist which are of interest in alloyed steels and cemented carbides. Tungsten hexacarbonyl is an important precursor for organic synthesis. 

Figure 3.21 Solvates (a) and polymorphs (b) characterized by their solubility curves in water. The phase diagrams of Mg(N03)2/H20 and NH4NO3/H2O are depicted in (a) and (b), respectively. Solvates are indicated by vertical lines in the binary system, thus characterizing intermediate compounds that can melt congruently or incongruently. In the case shown, different hydrates of magnesium nitrate containing 2, 6, and 9 mol water in the crystal...

Tellurium subhalides contain the series of isotypes Tc2X (X = Cl, Br, I). Solid solutions of the stable Te2Br and the metastable Te2l have been studied. Further examples of studies of ternary subhalides were based on selenium subhalides, with SeCl and a-/ 3-SeBr being the only known subhalides no intermediate binary compound exists in the Se-I system. The latter fact in i rticular stimulated the investigation of the ternary Se-Te-I system in order to find out whether there are distinct intermediate ternary subiodides and/or regions of ternary solid solutions based on the subiodide a-Tel. 

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