Metal halide systems

Fig. 16.68 Thu. structure of ZrC], a reduced metal halide system containing infinite melal-mctal bonds, showing double metal atom layers alternating with double chlorine atom layers. [From Corbett. J. D. An. Chem. Res. 1981. 14. 239. Reproduced with permission.]...

Similar laser-induced dissociation of "colored vapors and vapor complexes has been recently reported for a number of metal-halide systems ( 2, 50). 

Table 1 Derived spectroscopic and ab initio parameters of noble gas-metal halide systems ...

Ctudies of binary rare earth metal-metal halide systems have revealed not only a considerable number of new, reduced phases, but also a substantially new class of halides possessing a metallic rather than a truly reduced or localized character. The reduction properties of the chlorides, bromides, and iodides of the first four rare earth elements are summarized as follows in terms of the compositions of new lower phases or, where absent, the limiting solution compositions in mole % metal in liquid MX3 ... 

Comprehensive cryoscopic, calorimetric, and galvanic cell studies of alkali metal halide systems with a common anion and a common cation have been carried out. These measurements have shown that the enthalpy of mixing for these systems can, in general, be expressed by a parabolic type equation... 

From the above considerations it can be concluded that the slopes of the X versus 812 plots for the common earth alkali halide systems should increase in the sequence Mg < Ca < Sr < Ba. This was indeed experimentally observed. Except for the lithium halide-earth alkali metal halide systems, the data are well represented by the X versus 512 plot for each common earth alkali metal halide system. The slopes of X versus 5i2 plot increase when the radius of the common earth alkali metal cation is increasing. 

To the melts containing a trivalent cation belong a great number of systems of alkali metal halide-rare earth metal halide systems. Lanthanide halides play an important role in the production of lanthanide metals by molten salt electrolysis and they are also used in a number of applications ranging from lighting to catalysis, through pyrochemical reprocessing of nuclear fuel. 

Rice (1961) and Raleigh (1963) supposed that the concentration of electrons is proportional to the concentration of cations in the lower oxidation state. Such a condition is well fulfilled in metal-metal halide systems in the range of high concentrations of metal halide (when the metal is a minor component). However, in systems with comparable concentrations of both the cations, the situation is somewhat different. An electron can jump only when an electron donor has an electron acceptor in its neighborhood. The probability that such an acceptor is available is equal to the product x(Me +)-x(Me + " ). The exponential character of the temperature dependence of electrical conductivity is due to the fact that the concentration of cations in lower oxidation state increases with increasing temperature, which consequently increases the jump probability of the electron. 

Properties of the metal-metal halide systems have been studied since the first Davy s observations of colored melts near the cathode at the electrolysis of alkali metal hydroxides. However, already the knowledge of these molten systems was substantially improved 50 years ago by the pioneering work of Bredig et al. (1958), who investigated the phase equilibria in a number of alkali metal-alkali metal halide and earth alkali metal-earth alkali metal halide systems. Further interest was also aroused in the case of... 

The next characteristic feature of the metal-metal halide systems is the partial electronic conductivity caused by the presence of the same metallic atoms in two oxidation states. In general, the conductivity of the melt is given by the equation... 

As a consequence of impossibility to arrange particles in the liquid phase in one solution only, the formation of two liquids, which are not miscible, may occur. Such a situation can be frequently observed in glass-forming silicate melts in the region of high concentrations of SiOa. Partial miscibility in the liquid phase is quite uncommon in binaries of molten salts. Partial miscibility is more frequent in reciprocal salt systems and probably as a rule, in the high metal concentrations of the metal-metal halide systems. 

Eastman, E.D., Cubicciotti, D.D. Thurmond, C.D. (1950) in Temperature-Composition Diagrams of Metal-Metal Halide Systems, Nat. Nucl. Energy Ser., Div. IV, Chem. Met. Misc. Mater., Vol. 19B. Ed. QuiU, L.L., McGraw-Hill Book Co., Inc., New York, pp. 6-12. 

Vapors of Quasi-binary Metal Halide Systems. 174... 

Most of the vaporization studies by Knudsen effusion mass spectrometry, carried out for the determination of thermodynamic data of condensed phases, refer to alloys and to a smaller extent to oxide systems as shown by this article. In comparison to this only a few metal halide systems have been investigated. In addition to the study of elements and binary oxides or halides by far most of the... 

A significant amount of SSNMR data has been acquired for the alkali metal halide systems, MX (M = Li, Na, K, Rb, Cs X = Cl, Br, I). As the data for these systems are generally complementary in nature, this section combines the ... 

The power of this technique is also illustrated in metal-halide systems where compositional space... 

In the metal-halide system, the hydrogen producing reaction is written as [9]... 

The initial tests of the sodium dispersion-metal halide system were made with ferric chloride, fortunately, and with a nonaqueous solvent in which ferric chloride was soluble. Thus, ferric chloride was present as a solution and, consequently, presented maximum surface for contact with the sodium particles. This feature, coupled with the lower activation energy requirements, permitted the reaction to proceed at temperatures well below room temperature and established the operability of the method. The success of the initial (ferric chloride) tests lent encouragement to tests on other metal systems and prompted continued investigations when the initial runs at lower temperatures failed. The discovery of the threshold, or trigger, temperature for nickel (II) chloride reduction paved the way for successful reduction of other metal halides such as manganese (II) chloride, cobalt (II) chloride, and cadmium bromide. 

FiQUre 26 Spectral irradiance of metal halide system vs. global radiation. 

Reproduced from Kapustina Nl, Sokova LL. Makhaev VD, Borisov AP, Nikishin Gl. Oxidation of aliphatic alcohols with the lead tetraacetate-metal halide system under mechanical activation. Russ Chem Bull Int Ed 2000 49 1842-5 [Izv Akad Nauk Ser Khkn 2000 49 1870-3], with pennission of Springer. 

Lokken, D. A. Corbett, J. D. (1973). Rare Earth Metal-Metal Halide Systems. XV. Crystal Structure of Gadolinium Sesquichloride. A Phase with Unique Metal Chains, Inorg. Chem. 12, 556-559. 

The observation of electric transport in dense supercritical ionic phases stimulated the investigation of conductance in supercritical metals above 1500 °C and to pressures of about 2000 bar. The conductance of mercury was investigated and continuous metal-nonmetal transition was observed [25]. An impressive amount of further aspects of such metal-nonmetal transitions has been studied later in alkali metals and other fluids (see F. Hensel and coworkers) [25a]. A metal-nonmetal transition was also observed in cesium hydride and cesium in the liquid state at high hydrogen pressures [26] which corresponds to the earlier non-pressure work of Max Bredig [26a] with liquid metal-metal halide systems. 

Finally, Cohn " examined systematically the reactions of (CH3)2NPF2 with a series of halides taken from the first row of transition elements The metal halides studied were TiCU, FeCl3, NiBr2, CoBr2, CUCI2, CuCl, and GaCl3 as well as NaCl. No reaction was observed with NaCl. Four types of reactions were identified when (CH3)2NPF2 was mixed with metal halide systems. These are ... 

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