Systems containing tetravalent cations

The most important representatives of tetravalent elements are titanium and zirconium because of their uses as advanced construction materials in different technologies. Systems of titanium and zirconium fluorides and chlorides with alkali metal fluorides and chlorides, respectively, can be found in the Phase Equilibria Diagrams Database (1993). A number of compounds with various stoichiometry are formed in these systems, depending on the size of the titanium and zirconium cation and the polarization ability of the alkali metal. Some of these compounds are very stable and melt congruently even at relatively high temperatures. On the other hand, some compounds melt incongruently and their existence is limited to a certain temperature range. 

In the systems LiF-TiF4 and NaF-TiF4 there are no compounds present, while in the systems MF-TiF4 (M = K, Rb, Cs), only two congruently melting M3TiF7 and M2TiF6 compounds are formed. 

In the systems LiCl-TiCU, NaCl-TiCb, and RbCl-TiCb, no compounds are formed, while in the systems KCl-TiCb and CsCl-TiCb, the congruently melting compounds K2TiCl6 and Cs2TiCl6 originate respectively. 

However, among all of the above mentioned compounds, the technologically most important are the K2TiF6 and K2ZrF6, because of their frequent use in the electrochemical deposition of titanium and zirconium and the electrochemical synthesis of titanium and zirconium diborides. 

Titanium diboride exhibits a high melting point, electronic conductivity, wetability by molten aluminum, and a resistance towards chemical attack of aluminum and molten fluorides. Due to these properties, TiB2 is considered to be the most promising material for inert cathodes in aluminum electrolysis. Also zirconium diboride belongs to the category of promising constructive materials due to its favorable properties. 

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In the preparation of Mo/KL, the addition of 1 was stopped when pH of the solution was lowered to about 3. The resulting Mo/KL contained only 2.1 wt% (74% of added molybdenum clusters) of molybdenum. Chlorine was absent, which indicates that the cluster 1 acted as a tetravalent cation. The LTL structure is characterized by a monodimensional system of channels, whose diameter (0.70 nm) [14] is close to the size of the cluster 1. It is conceivable that, once the cluster 1 was incorporated into an LTL main channel and present at a site near the external surface, the sites deep in the channel are no more accessible to another cluster. 

In the following sections, the results of Raman spectroscopic studies of the systems containing monovalent to tetravalent cations will be presented. 

Some mono-, di-, and tetravalent cations combine with the rare earths to form ternary sulfates. Tl, Ag, Cd % and Sn" compounds have been reported (Pascal, 1959), and more recently Ce sulfates containing HjO or Ti (probably as TiO " ion) as counterions (Belokoskov et al., 1979 Gatehouse and Pring, 1981). For a recent study of the La2(S04)j-Ag2(S04)3 system, see Campbell et al. (1983). 

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