Tantalic chloride

Potassium heptafluorotantalate, K2TaF7, or as it is called by its commercial name K-salt, is a starting material for tantalum metal production. K-salt is produced by adding potassium fluoride, KF, or potassium chloride, KC1, to a tantalum strip solution that results from a liquid-liquid extraction process. In order to prevent hydrolysis and co-precipitation of potassium oxyfluoro-tantalate, a small excess of HF is added to the solution [24]. Another way to avoid the possible formation and co-precipitation of oxyfluoride phases is to use potassium hydrofluoride, KHF2, as a potassium-containing agent. The yield of the precipitation depends mostly on the concentration of the potassium-containing salt and is independent of the HF concentration [535]. 

Tantalium (V) chloride (tantalium pentachloride) [7721-01-9] M 358.2, m 216.2 , 216.5-220 b 239 /atm., d 3.68. Purified by sublimation in a current of CI2. Colourless needles when pure (yellow when contaminated with even less than 1% of NbCls). Sensitive to H2O, even in cone HCl it decomposes to tantalic acid. Sol in EtOH. [J/ICS 80 2952 1958, Handbook of Preparative Inorganic Chemistry (edBrauer) Vol II 1302 7965]. 

The tantalates are produced by a solid-state reaction between Ta205, Nb205, and Y203 in a 14-hour preliminary firing at 1000°C and a crystallization firing with lithium chloride or lithium sulfate as flux. 

Tantalum pentoxide is insoluble in solutions of caustic alkalis and alkali carbonates, but on being fused with these substances reacts to produce the alkali tantalates. Tantalates of the metals are obtained by double decomposition, using a soluble alkali tantalate and a soluble salt of the metal. Tantalates of the alkaline earths have also been obtained by fusing tantalum pentoxide with the chloride of the alkaline earth. 

The soluble alkali tantalates undergo ready hydrolysis when their aqueous solutions are boiled, precipitation of a more add salt takes place and some alkali base passes into solution. Separation of the base in this manner is naturally favoured by the presence of acids, and even so weak an acid as carbon dioxide or hydrogen sulphide pretipitates tantalic add or an acid salt with the stronger adds (sulphurous acid, sulphuric add, hydrochloric acid, nitric add, etc., but not with hydrofluoric add) predpitation of tantalic add takes place readily, but excess of the strong mineral add redissolves the predpitate. Potassium chloride... 

Ammonium Tantalate, (NH4)a0.3Ta205.5H20, is obtained as a flocculent precipitate by the addition of ammonium chloride to a solution of 4 8 sodium tantalate.2 An ammonium potassium tantalate, (NH4)20.K20.4Ta205.5Ha0, has also been obtained by the same reaction, using potassium tantalate. 

Iron Tantalates.—The meta-salt, Fe0.Ta206, has been obtained more or less pure by fusing tantalum pentoxide and ferrous fluoride with excess of potassium chloride.8 Iron tantalates occur naturally in niobites and tantaMtes. The ore tapiolite has the approximate composition FeO.Ta2Os the tantalum may be partially substituted by niobium.9... 

Sodium Tantalales.—4 3 Sodium tantalate, 4Na20.8Ta206.25H20, is prepared by fusing tantalum pentoxide with caustic soda in a silver crucible excess of caustic soda is removed by washing with water, and the residue is crystallised from hot water. Another method consists in adding a concentrated solution of sodium chloride to the aqueous extract from a fused mixture of tantalum pentoxide and potassium carbonate, when the salt separates as a dense, micro-crystalline powder. It forms six-sided plates, a c=l 1-0167. It loses most of its water of crystallisation between 105° and 110° C., but the remainder (apparently five molecules) appears to be water of constitution, as its removal takes place only at much higher temperatures, with decom-... 

The reaction of phosphorus pentachloride with ammonium chloride is tantalizingly complex and has been the subject of numerous investigations (21). Cyclic oligomers and linear products are formed, and... 

Tantalic acid or tantalum hydroxide is usually given the formula HTaO>, although the composition undoubtedly varies rather widely. It is precipitated as a gelatinous mass when the chloride is diluted, but it may be obtained in crystalline form by precipitation with dilute ammonia. When the crystalline form is ignited it glows brilliantly and forms Ta208. The freshly prepared acid dissolves quite readily in acids. 

Fowler 1991). Insoluble species of tantalum, administered orally to rats, are poorly absorbed from the gastrointestinal tract, with total excretion accounted for in the feces. Ta administered orally to rats as soluble potassium tantalate was rapidly excreted almost exclusively via the fecal route less than 2% of the dose was retained after 1 day (Fleshman etal. 1971). More than 96% of the administered dose was excreted after 3 days, and less than 0.5% was recovered in urine after 7 days, although more than 97% of the total dose had been excreted. After absorption, Ta was primarily localized in the bone compartment, which retained over 40% of the total body burden after 14 days, and in the kidneys (Fleshman et al. 1971). The biological half life of the soluble, short-lived radionuclide (tj2 = 9.3 min) Ta given as Ta-chloride or Ta-oxide to dogs via intravenous administration was 190 min, with 78% of the Ta being found in the plasma ( 33% with the plasma protein fraction) and the remainder in red blood cells (Wilson etal. 1987). The distribution of soluble Ta administered intravenously to mice demonstrated Ta accumulation primarily in kidney (17% of the dose), followed by liver (9%) and blood (8.5%) (Wilson et al. 1987). 

Conversion of the potassium niobate/tantalate solution to the corresponding oxides is via the insoluble sodium niobate and tantalate. These are readily precipitated by the addition of a sodium salt, solid crystalline sodium chloride being preferred in economic grounds, i.e. ... 

Various catalytic systems such as boron trifluoride [62,63], aluminum chloride [64-67], tantal halides [68], zirconium halides [69,70], zeolites [71-73], molecular sieves containing metallic oxides [74], ion exchangers [75], fluoroal-kane sulfonic acid [76], and montmorilonite [77] have been used to promote oligomerization of long-chain alkenes, cycloalkenes, and dienes. 

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