Melting diagrams

Additional evidence of the reaction described in Equation (11) is the section of the Li2C03 -Nb02F system s melting diagram presented in Fig. 9 [87]. 

Fig. 9. Melting diagram of LifCOi - NbC>2F system. Reproduced from [87], A. I. Agulyansky, V. A. Bessonova, V. Y. Kuznetsov, V. T. Kalinnikov, Zh. Neorg. Khim. 29 (1984) 1066, Copyright 1984, with permission of Nauka (Russian Academy of Sciences) publishing.

Molten salt investigation methods can be divided into two classes thermodynamic and kinetic. In some cases, the analysis of melting diagrams and isotherms of physical-chemical properties such as density, surface tension, viscosity and electroconductivity enables the determination of the ionic composition of the melt. Direct investigation of the complex structure is performed using spectral methods [294]. 

Three conceptual steps can be discerned in the definition of the ionic structure of fluoride melts containing tantalum or niobium. Based on the very first thermodynamic calculations and melting diagram analysis, it was initially believed that the coordination numbers of tantalum and niobium, in a molten system containing alkali metal fluorides, increase up to 8. 

Fig. 51. Melting diagrams of NbF5 - MF systems, where M = Li, Na, K (after Bizot and Makek-Zadeh [77]).

Analysis of the melting diagrams led to the conclusion that fluoride, fluoride-chloride and oxyfluoride-chloride melts containing niobium contain the complex ions NbF83 NbF7Cl3 Nb02F43 ... 

Iuchi and Matsuchima [305] and Zui Bin-Sin, Lushnaya and Konstantinov [306] investigated the melting diagram of the ternary system K2TaF7 - KF -KC1 and observed the compound K3TaF7Cl along with its initial components. 

An analysis of the melting diagram led to the conclusion that, in fluoride and fluoride-chloride melts, tantalum forms the complex ions TaFg3 or TaF7Cl3, respectively [37,306]. 

The results were presented in the form of isotherms, in which the properties are plotted versus the concentration. Nevertheless analysis of the isotherms was made based on available melting diagrams approach that the melts consist of TaFg3 and TaF7Cl3 complex ions. However, according to this general conception [312-314], the isotherm of the surface tension must, in such a case, have either a minimum or at least display prominence of the dependence in the direction of the concentration axis. 

Fayalite (melting point 1205°C) and forsterite (melting point 1890°C) form continuous solid solutions (the melting diagram of their binary mixtures correspond to the type exemplified in Fig. 2.28). Phase equilibria as a function of pressure, show, however, transition into the spinel structure. (cF56-MgAl204, spinel structural type). 

The lowering of the melting point is also the same for these metals when the electron concentration instead of the atomic concentration is plotted against the temperature in the melting diagram. 

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