Niobium synthesis

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... 

The synthesis of tantalum and niobium fluoride compounds is, above all, related to the fluorination of metals or oxides. Table 3 presents a thermodynamic analysis of fluorination processes at ambient temperature as performed by Rakov [51, 52]. It is obvious that the fluorination of both metals and oxides of niobium and tantalum can take place even at low temperatures, whereas fluorination using ammonium fluoride and ammonium hydrofluoride can be performed only at higher temperatures. 

Synthesis of the compounds from such HF solutions is performed by adding soluble fluoride compounds to the tantalum or niobium solution or by recrystallization of prepared fluoride compounds from water or HF solutions of different concentrations. In the first case, the composition of the compounds obtained depends on the ratio between Ta/Nb and the added metal and on the initial concentration of the HF used, whereas in the second case, it depends only on the HF concentration. 

Potassium-containing tantalum and niobium fluoride compounds can be precipitated from HF solutions as described previously (see Fig. 3 and 4). Ritchie and Mitra [59] described the synthesis of K.2TaF7 in an HF solution, based on the following interaction (5), using TaCl5 as a precursor ... 

Attempts to obtain fluoride compounds of niobium and tantalum with alkali earth and some transitional metals were made as early as one hundred years ago, but synthesis and identification methods were described only at later times. 

The results available on the synthesis of niobium and tantalum fluoride compounds from aqueous solutions are in good correlation with the concept of... 

Another anhydrous solvent that is frequently used for the synthesis of tantalum and niobium fluoride compounds is bromine trifluoride, BrF3. At ambient temperature, bromine trifluoride is light yellow liquid characterized by a boiling point of 126°C, a melting point of 9°C and a density of 2.84 g/cm3 at melting temperature. 

The most universal method for the synthesis of tantalum and niobium fluoride compounds is based on direct interaction between their pentafluorides, TaF5 or NbFs, and fluorides of other metals. Some physical-chemical properties of these compounds are presented in Table 8 [71, 72]. 

Niobium dioxyfluoride, Nb02F, and tantalum dioxyfluoride, Ta02F, can be successfully used as precursors for the synthesis of many oxyfluoride compounds of niobium and tantalum. Systematic investigations performed on MeC>2F - M2CO3 systems, in which Me = Nb or Ta and M = alkali metal, provided necessary information on optimal synthesis procedures and imparted some conformity on the mechanism of the chemical interaction between the components. 

Hydrofluoride synthesis is based on the simultaneous fluorination by ammonium hydrofluoride of niobium or tantalum oxides with other metals compounds (oxides, halides, carbonates etc.) [105]. Table 13 presents some properties of ammonium hydrofluoride, NH4HF2 [51, 71]. Ammonium hydrofluoride is similar to anhydrous HF in its reactivity, but possesses some indisputable advantages. The cost of ammonium hydrofluoride is relatively low, it can be dried and handled easily, recycled from gaseous components, and its processing requires no special equipment. 

Thus, the sequence of phases that are formed in hydrofluoride synthesis of lithium-niobium fluoride compounds is (NH4)3NbOF6 - (NH NbOFs -LiNbOF4-Li2NbOF5. 

For a long period of time, molten salts containing niobium and tantalum were widely used for the production by electrolysis of metals and alloys. This situation initiated intensive investigations into the electrochemical processes that take place in molten fluorides containing dissolved tantalum and niobium in the form of complex fluoride compounds. Well-developed sodium reduction processes currently used are also based on molten salt media. In addition, molten salts are a suitable reagent media for the synthesis of various compounds, in the form of both single crystals and powdered material. The mechanisms of the chemical interactions and the compositions of the compounds depend on the structure of the melt. 

This monograph compiles the latest research on the chemistry of complex fluorides and oxyfluorides of tantalum and niobium, and covers synthesis and fluorination processes, crystal structure peculiarities and crystal chemical classification, as well as the behavior of complex ions in fluorine solutions and melts. 

Niobium, tris(diethyldilhiocarbamato)oxy-stereochemistry, 1,82 structure, 1, 83 Niobium, tris(oxa ato)oxy-stereochcmistry, 1, 82 Niobium, tris(phcnylcncdirhio)-structure, 1, 63 Niobium alanate, 3, 685 Niobium complexes alkyl alkoxy reactions, 2, 358 amides, 2,164 properties, 2, 168 synthesis, 2, 165 applications, 6,1014 carbamicacid, 2, 450 clusters, 3, 672,673,675 hexamethylbenzene ligands, 3, 669 cyanides synthesis, 2, 9 p-dinitrogen, 3, 418 fluoro... 

Using an electron-gun source, tungsten atoms were reacted with benzene, toluene, or mesitylene at 77 K, to form the expected (arene)2W complex (42) in a yield of 30%, compared with the —2% yield from the previously published, bis(benzene)W synthesis (32). These arene complexes are reversibly protonated, to give the appropriate [(T7-arene)2WH] species. By using the same technique, the analogous, niobium complexes were isolated (43). 

Scheme 26 Synthesis of rhenium and niobium polysulfido complexes from the corresponding doubly bonded complexes...

The first alkali metal-niobium-arsenic compounds were synthesized by accident while attempting the synthesis of alkali-metal main-group arsenides at relatively high temperature. It turns out that niobium and tantalum containers react readily... 

Synthesis of nanodot arrays using self-assembled niobium oxide nanopillar mask by reactive ion etching... 

Li J, Badding ME, DiSalvo FJ (1992) New layered ternary niobium teUurides Synthesis, structure, and properties of NbMTe2 (M = Fe, Co). Inorg Chem 31 1050-1054 Tremel W, Kleinke H, Derstroff V, Reisner C (1995) Transition metal chalcogenides New views on an old topic. J Alloy Compd 219 73-82... 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

Recently, we succeeded in the synthesis and structural characterization of first niobium-containing metallasilsesquioxane complex. In analogy to the corresponding reactions with titanium tetraalkoxides, niobium pentaethoxide cleanly reacts with 3 in a 1 1 molar ratio to give high yields of dimeric [Cy7Si70i2Nb0Et( U-OEt)]2 (149) as a colorless, crystalline solid (Scheme 49). 

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