Colloidal tantalum

The reduction of K2TaF7 can also be performed using sodium vapors [584]. This process is conducted at an Na pressure as low as 0.1 torr, which enables the removal of interferring gases such as N, O and H20. The interaction begins at 350°C. The temperature further increases up to 800°C to prevent the condensation of sodium and the formation of colloidal tantalum powder. The product of the interaction is removed from the reactor after cooling and treated with boiled HC1 and HF solutions. The method enables the production of coarse grain tantalum powder with 99.5% purity. 

Colloidal Tantalum.—A sol of tantalum has been prepared by sparking tantalum electrodes immersed in wobutyl alcohol using an induction coil. The sol appears brownish-black by transmitted light and black by reflected light it keeps only for one to two weeks.6... 

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. 

Preparation of Motallic Tantalum—Colloidal Tantalum—Physical Properties of the Metal, Optical Properties, Are and Spark Spectra—Chemical Properties—Electromotive Behaviour—Atomic Weight—Alloys. 

The predominant oxidation stale of the element is (V). There is some evidence that the (IV) state is obtained under certain reduction conditions. When the pentapositive form is not in the form of a complex ion it may exist in solution as PaC>2+. The compounds are very readily hydrolyzed in aqueous solution yielding aggregates of colloidal dimensions, thus showing marked similarity to niobium and tantalum in this respect. These properties play a dominant role in the chemical properties of aqueous solution, because the element is so easily removed from solution by hydrolysis and adsorption Protactinium coprecipilates with a wide variety of substances, and it seems likely that the explanation for this lies in the hydrolytic and adsorptive behavior. 

Sidorova, M.P. et al., Electrokinetic properties of tantalum oxide deposited onto a model substrate in NaCI and LiCl solutions. Colloid J., 59, 528, 1997. 

Nagayasu, T., Imamura, K., and Nakanishi, K., Adsorption characteristics of various organic substances on the surfaces of tantalum, titanium and zirconium, J. Colloid Interf. Sci., 286,462, 2005. 

The aim of this contribution is to present data on the preparation of catalysts containing as embedding species a large family of eolloids such as colloids of ruthenium, platinum, or palladium-gold alloys and triflate derivatives such as lanthanum and silver triflate or tert-butyldimethylsilyltrifluoromethanesulfonate (BMSTM). Silica, zirconia and tantalum oxides were used as carrier. All these preparations considered the polymeric sol-gel route using as starting materials silicon, zirconium or tantalum alcoxides. 

Following this route, catalysts with a large spectrum of properties resulted. Only silica embedded colloid catalysts exhibited excellent hydrogenation properties. Mixing the silica with a second oxide like tantalum led to support acid properties as resulted from NH3-FTIR measurements, which conferred to these catalysts bi-functional properties. Fig. 2 shows in-situ NH3-DRIFT spectra. The adsorption of NH3 is consistent with the formation of a new band at 1460 cm for SPT2, and 1440 cm for TSPT2 as a contribution of v(H-N-H) in adsorbed NH4. The bands at 3240, 3045, and 2840 cm result from the same contribution. The adsorption of NH3 also led to the disappearance of the band due to adsorbed water. These data indicated a Bronsted acidity only for tantalum containing catalysts. No Lewis acid sites were detected. 

A new method was developed using a modified polishing device for measuring galvanic corrosion during chemical mechanical planarization (CMP) of copper and tantalum [22]. CMP is used to pofish on a microscopic scale. In most cases, this is done using a colloidal slurry of abrasive microscopic particles. 

If efficient active sites shall be created by stabilizing the molecular species at the surface of a well-defined phase, as in the case of V0x/Ti02 - anatase catalysts, the better activity in NO SCR was achieved by cocondensation of the dopant alkoxide with the surface groups of preformed colloidal particles of the matrix precursor, followed by gelation [76]. A similar approach of modifying the matrix precursor sol with dopant molecules yielded well-dispersed tantalum species at the silica surface, efficient in selective oxidation of pyrimidine thioether [77]. 

Jiang S, Guo Y, Wang C, Qu X, Li L (2007) One-step sol-gel preparation and enhanced photocatalytic activity of porous polyoxometalate-tantalum pentoxide nanocomposites. J Colloid Interface Sci 308 208-215... 

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