Tantalum hydrates

Tantalum pentoxide [1314-61 -0] Ta20, is prepared by calcining tantaUc acid or hydrated tantalum oxide [75397-94-3] Ta20 at... 

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

It is, therefore, required that all initial compounds be dried properly prior to performing the reduction. This procedure is not at all trivial and refers, first of all, to the diluent salts, and especially to potassium fluoride, KF, which is characterized by a strong hygroscopic property and a tendency to form stable crystal hydrates. The problem of contamination due to hydrolytic processes can usually be resolved in two manners. The first is to apply another tantalum-containing complex fluoride compound that does not undergo hydrolysis. The second involves the adjustment of the reduction process parameters and use of some additives that will "collect" the oxygen present, in the form of water, hydroxyl groups or other compounds. 

Tantalum pentoxide [1314-61-0], Ta is prepared by calcining tantaUc acid or hydrated tantalum oxide [75397-94-3], Ta2Os H20, at temperatures between 800 and 1100°C. This oxide hydrate is produced by adding gaseous or aqueous ammonia to the solvent extraction produced aqueous tantalum solution in a continuous (29) or batch process. 

Within the (M6Xi2) + (X = Cl, Br q = 2-4) cluster halides, the only series that cover all three oxidation states are the tantalum halide hydrates and the haloanions [(MsXi Xg] -. The isolation of [(Ta6Cli2)Cl2(PR3)4](PF6) (n = 1, 2) led to the first complete series of group VA cluster stabilized by an organic ligand. 

Conversion of the separated fluorides into the corresponding oxides is effected by boiling with concentrated sulphuric acid until free from fluorine, and then hydrolysing the product by boiling with water. Alternatively, the hydrated acids are precipitated by the addition of ammonia to the solutions of the double fluorides.4 Niobium pentoxide, Nbg05, or tantalum pentoxide, TaaOs, is obtained on ignition of the precipitated hydrate. 

A method of separation which avoids the preparation of the double fluorides consists in fusing the mixed niobic and t an tali c acids with sodium carbonate and nitrate, the product is digested with warm water and a current of carbon dioxide is passed through the solution. It is claimed that only tantalic acid is precipitated.5 This process has, however, been the subject of adverse criticism.6 Partial separation of niobium from tantalum can be effected by warming the mixed, freshly precipitated, hydrated oxides with a mixture of hydrogen peroxide and hydrochloric acid the niobium dissolves readily, while the tantalum dissolves only sparingly.7... 

The analysis of ferrotantalum alloys and of tantalum steels also involves the conversion of the tantalum present into the pentoxide. The material is dissolved in hydrofluoric add and nitric acid, evaporated to dryness, and the residue fused with potassium hydrogen sulphate extraction with dilute hydrochloric acid and hydrolysis yield a predpitate of hydrated tantalic pentoxide, the iron remaining in solution.7... 

A hydrated tantalum sesquioxide, Taj03.a H20, is stated to be formed by the addition of caustic soda to solid tantalum trichloride (Buff and Thomas, Zeitsch. anorg. Ghent., 1925, 148, 3 Ber., 1922, 55, 1473). 

Metallic tantalum and tantalum pentoxide are both dissolved by hydrofluoric add, but evaporation of the solutions yields a residue which consists either of a tantalum oxyfluoride of variable composition or of the hydrated pentoxide. 

Tantalum Pentoxide, Ta205, is one of the commonest compounds of tantalum. The anhydrous substance is produced by direct oxidation of the metal or by ignition of hydrated tantalum pentoxide, which is obtained by the methods described below. The removal of niobium and other metals has been described when dealing with the extraction of tantalum and niobium from thdr natural ores. 

Hydrates of Tantalum Pentoxide, Colloidal Tantalum Pentoxide, Tantalic Acid.—When tantalum pentachloride or pentabromide is treated with water, or when a solution of a tantalate is boiled with dilute acids, a gelatinous predpitate of more or less hydrated tantalum pentoxide is thrown down. Insoluble tantalates on fusion with potassium hydrogen sulphate and extraction of the melt with water give the gel. In dealing with double fluorides of tantalum it is necessary to remove all the hydrofluoric add by evaporation with concentrated sulphuric acid, otherwise double fluorides are obtained. 

As in the case of hydrated niobium and vanadium pentoxides, it is a difficult matter to remove traces of mineral acids from the precipitate. Treatment with water gives rise to a cloudy hydrosol which passes through an ordinary filter. This can be prevented by addition to the wash-water of a small quantity of ammonia or acetic acid.4 In the preparation of anhydrous tantalum pentoxide, traces of adds can be removed by igniting the gel in admixture with a small quantity of ammonium carbonate. 

Hydrated tantalum pentoxide or tantalic add is very comparable in its properties to niobic acid (see p. 157). It is soluble in excess... 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

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