Congruently melting

Addition of the appropriate amount of water to anhydrous H3PO4, or crystallization from a concentrated aqueous solution of syrupy phosphoric acid, yields the hemihydrale 2H3PO4.H2O as a congruently melting compound (mp 29.3 "). The crystal structure shows the presence of 2 similar H3P()4 molecules which, together with the H2O molecule, are linked into... 

The largest crystallization field belongs to K3Nb02F4, which undergoes congruent melting at 986°C. 

Safonov et al. 330) also investigated the In-Te-I system by DTA and X-ray diffraction. The system contains three, congruently melting, ternary compounds InTel, Inl3-2Tel4 and InIs-STel, of which the latter two are out of the scope of this review. InTel melts congruently at 475°C. It forms part of the quasibinary cuts In Tea-Inla and Inl-Te, where the sections InTel-In Tes, InTel-Inia, InTel-Ini, and InTel-Te are all of the eutectic type (80). 

The phase diagram for the Sr-Au system shows three congruently melting phases, /3-SrAu (970°C), SrAu2 (1085°C) and SrAu, (1040°C) four phases formed in peritectic reactions are also observed, Sr Au (640°C), SrjAu (590°C), y-Srj Au (750°C) and 5-Sr,Au2, which has a limited stability range from the eutectoid (725°C) to the peritectic reaction (770°C). Independent structural investigations confirm the forma-... 

When it melts, however, the melt then decomposes into two separate phases. On either side of the congruently- melting composition is a phase... 

Nonstoichiometric Nature of Some Binary Congruently Melting... 

System in which the two components form a compound p>ossessing a congruent melting point. ... 

Figure 2.18. Examples of binary phase diagrams in each of which one stoichiometric phase is formed. In the Mg-Ge system we have the congruently melting Mg2Ge (33.3 at.% Ge) in Au-Sb, AuSb2 is formed through a peritectic reaction. In the Pt-Ag system one compound at 47 at.%...

In the Au-Bi system the compound Au2Bi is stable in a restricted range of temperature only it is formed by a peritectic reaction (371°C) and, at a lower temperature (116°C), it is decomposed according to the eutectoidal reaction Au2Bi — (Au) + (Bi). In the Zn-Te system, finally, we have the congruently melting compound ZnTe. In this system a miscibility gap in the liquid state may also be noticed. 

Figure 2.19. Examples of systems in which intermediate phases corresponding to small composition ranges are formed. These are SnTe (congruent melting), HfRu (congruent melting), ZrV2 (peritectic formation) and TaV2 (formed through a solid-state reaction).

Figure 3.3. Schematic representation of the diagrams for the alkali metals with a selected number of elements of the p-block. In each box the solid intermediate phases are represented in the positions approximately corresponding to their compositions (long bars congruent melting phases short bars non-congruent phases). In the top part of each box every mark corresponds to a characteristic composition of the liquid phase for which the formation of an associate ( liquid compound ) may be suggested, for instance by the presence of an extremum in the trend of some property of the liquid phase. The symbol 2 L shown for certain ranges of compositions in a few diagrams indicates the presence of a miscibility gap in the liquid state, that is two liquid phases.

Figure 3.50. The Yb-Cd binary phase diagram. The congruently melting compound YbCd57 is the first stable binary quasicrystal identified.

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