More Complex Fluorides

DeCaF treats soil, sludges, solids (e.g., slag), residues, and sediments contaminated with radioactive elements and other hazardous constituents. The technology has potential applications in the treatment of heavy metals. The technology can treat uranium-contaminated calcium fluoride matrices, rare-earth ore residues, and fluorspar contaminated with uranium. The technology can also extract more complex fluoride by-products. 

More complex fluorides prepared similarly are exemplified by the following CaPbOj to CaPbFg and BaFeO 5 to BaFeF. Reactions of F with mixtures of compounds are also carried out to prepare complex fluorides ... 

Unlike the MSR, the FHR use solid fuel and a clean liquid salt as a coolant (i.e., a coolant with no dissolved fissile materials or fission products). For the MSR, a major constraint was the requirement for high solubility of fissile materials and fission products in the salt another one for suitable salt reprocessing. For the FHR, these requirements do not exist. The requirements mainly include (1) a good coolant, (2) low coolant freezing points, (3) stability under irradiation, and (4) application-specific requirements. As a result, a wider choice of fluoride salts can be considered. In all cases, binary or more complex fluoride salt mixtures are preferred because the melting points of fluoride salt mixtures are much lower than those of single-component salts. 

A substantial portion of fhe gas and vapors emitted to the atmosphere in appreciable quantity from anthropogenic sources tends to be relatively simple in chemical structure carbon dioxide, carbon monoxide, sulfur dioxide, and nitric oxide from combustion processes hydrogen sulfide, ammonia, hydrogen chloride, and hydrogen fluoride from industrial processes. The solvents and gasoline fractions that evaporate are alkanes, alkenes, and aromatics with relatively simple structures. In addition, more complex... 

Hydrogen fluoride adds to more complex molecules, such as unsaturated steroids, to give fluorinated derivatives [/, 8] Low temperatures and inert diluents, such as tetrahydrofuran or methylene chloride, are generally employed. With bicyclic unsaturated terpenes, rearrangements often accompany addition to the double bond [/]. 

The alkylation process possesses the advantages that (a) a wide range of cheap haloalkanes are available, and (b) the substitution reactions generally occur smoothly at reasonable temperatures. Furthermore, the halide salts formed can easily be converted into salts with other anions. Although this section will concentrate on the reactions between simple haloalkanes and the amine, more complex side chains may be added, as discussed later in this chapter. The quaternization of amines and phosphines with haloalkanes has been loiown for many years, but the development of ionic liquids has resulted in several recent developments in the experimental techniques used for the reaction. In general, the reaction may be carried out with chloroalkanes, bromoalkanes, and iodoalkanes, with the reaction conditions required becoming steadily more gentle in the order Cl Br I, as expected for nucleophilic substitution reactions. Fluoride salts cannot be formed in this manner. 

Similar considerations apply to oxidation. An anion which is considerably more stable than water will be unaffected in the neighbourhood of the anode. With a soluble anode, in principle, an anion only needs be more stable than the dissolution potential of the anode metal, but with an insoluble anode it must be stable at the potential for water oxidation (equation 12.4 or 12.5) plus any margin of polarisation. The metal salts, other than those of the metal being deposited, used for electroplating are chosen to combine solubility, cheapness and stability to anode oxidation and cathode reduction. The anions most widely used are SOj", Cl", F and complex fluorides BF4, SiFj , Br , CN and complex cyanides. The nitrate ion is usually avoided because it is too easily reduced at the cathode. Sulphite,... 

Predominant formation of either complex fluoride or complex oxyfluoride depends on the interaction rates ratio of processes (25) and (26). The relatively high interaction rates of (27) and (28) lead to the synthesis of simple fluorides or oxyfluorides, respectively. With the availability of two or more cations in the system, the ammonium complex fluorometalates interact forming stable binary fluorides or oxyfluorides or mixtures thereof. 

The hydrofluoride method can be used successfully both for the preparation of complex fluoride compounds and of complex oxides. The main advantage is that the synthesis is performed at relatively lower temperatures. In addition, the complex oxide material is formed through its respective fluoride compound and the product obtained is therefore more consistent. For instance, Co4Nb209 can be prepared using the hydrofluoride method at 900-1100°C, whereas the regular synthesis, based on the interaction of simple oxides, requires extended treatment at about 1400°C. 

In the case of a mixture of hydrofluoric and sulfuric acids, the process is more complex. It can be noted that sulfuric acid most probably interacts mainly with iron and manganese, whereas hydrofluoric acid serves mostly in the dissolution of tantalum and niobium and their conversion into soluble fluoride complexes. Nevertheless, due to the high acidity of the solution, here too the formation of hexafluorotantalate and hexafluoroniobate complex ions, TaF6" and NbF6, is expected. Hence, it is noted that the acid dissolution of tantalum-and niobium-containing raw material leads to the formation of hexafluoro-acids — HTaF6 and HNbF6. 

Although the elements tantalum and niobium were discovered more than 200 years ago in the form of oxides, the true beginning of the chemistry of tantalum and niobium was the discovery and investigation of complex fluorotantalates and fluoroniobates of alkali metals. Application of complex fluoride compounds enabled the separation of tantalum and niobium and in fact initiated the development of the industrial production of the metals and their compounds. 

Kuwajima (75) has provided full details of the regiospecific monoalkylation of carbonyl compounds via their silyl enol ethers, using stoichiometric amounts of fluoride ion. Noyori (76) has given more information on the use of the complex fluoride source (2) (Chapter 18)... 

Applications to complex fluorides should be possible using the more conducting solid electrolytes now available. 

III, F. More phase diagrams of complex fluorides have been explored using Knudsen cell mass spectrometry (13, 15), and electron impact studies have yielded enthalpies and bond energies (1,3). The heat of formation of MoFmi) has been confirmed (12). Solid state cells have been used with lanthanide trifluorides (24) and NaNiF3 (21). 

More complex examples of the use of this notation may be given by the structures of typical fluorides for which ionic-type coordination formulae are here reported ... 

These observations lead to a general conclusion that the same supporting electrolyte should be used for a valid comparison of parameters obtained for various organic adsorbates on the same electrode. The situation becomes more complex when different electrodes are to be studied, because some ions (e.g., fluorides) which are not adsorbed on the Hg electrode do adsorb on Ag " and probably also on the Au electrodes. Large ions of small charge density, such as PFg, BFj, and ClOi, seem to be more weakly adsorbed on solid electrodes than small F ions. All the... 

Being a fluoride ion acceptor, SbCF enhances the acidities of HF and HSO3F solutions, forming SbFe ion or more complex species. Thus, SbFs in... 

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