Of tantalum oxides

During World War II, production of butadiene (qv) from ethanol was of great importance. About 60% of the butadiene produced in the United States during that time was obtained by a two-step process utilizing a 3 1 mixture of ethanol and acetaldehyde at atmospheric pressure and a catalyst of tantalum oxide and siHca gel at 325—350°C (393—397). Extensive catalytic studies were reported (398—401) including a fluidized process (402). However, because of later developments in the manufacture of butadiene by the dehydrogenation of butane and butenes, and by naphtha cracking, the use of ethanol as a raw material for this purpose has all but disappeared. 

The fluorination of tantalum oxide, Ta205, is described by Rakov [51]. The interaction begins at a temperature of 156-190°C, yielding heptafluorotantalate of ammonium ... 

The second solution that results from the liquid-liquid extraction process is a high-purity niobium-containing solution. This solution is used in the preparation of niobium oxide, Nb205. The process is similar to the above-described process of tantalum oxide preparation and consists of the precipitation of niobium hydroxide and subsequent thermal treatment to obtain niobium oxide powder. 

Fig. 132. Distribution of tantalum oxide between cells of pilot extraction system, for organic and aqueous phases. Reproduced from [473], A. Agulyansky, L. Agulyansky, V. F. Travkin, Chemical Engineering and Processing 43 (2004) 1231, Copyright 2004, with permission of Elsevier.

Fig. 132 shows the content distribution of tantalum oxide among the cells, for the organic and aqueous phases. 

The tantalum strip solution was used for the preparation, by precipitation and thermal treatment, of tantalum oxide. The product was determined to be of high purity grade. Table 62 presents typical analysis results. 

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. 

Intratracheal administration to guinea pigs of 100 mg of tantalum oxide produced transient bronchitis, interstitial pneumonitis, and hyperemia, but it was not flbrogenic. There were some slight residual sequelae in the form of focal hypertrophic emphysema and organizing pneumonitis around metallic deposits, and there was slight epithelial hyperplasia in the... 

Schepers GWH The biologic action of tantalum oxide. AMA Arch Ind Health 12 121-123, 1955... 

Tantalum metal is prepared from potassium fluotantalate or tantalum pen-toxide produced from the ore concentrate by solvent extraction or fractional crystallization as described. The metal is produced industrially by Balkes electrolysis process. Fused potassium fluotantalate is electrolyzed at 900°C in a cast iron pot. While the latter serves as a cathode, a graphite rod is used as the anode. A small amount of tantalum oxide is added to the melt. The unreduced potassium fluotantalate is separated from the tantalum metal produced by leaching with water. Impurities are removed from the metal by acid wash. 

Tantalum is resistant to corrosion because a thin film of tantalum oxide forms when tantalum is exposed to oxygen. The metal oxide acts as a protective layer. The oxide also has special refractive properties that make it ideal for use in camera lenses. 

Ostromyslenskii (Ostromisslenskii) reaction. Dehydrogenation of ethanol over copper-containing catalysts and conversion of the acetaldehyde ethanol mixture to butadiene by passage at high temperature over silica gel containing a small amount of tantalum oxide. 

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. 

The separation of tantalum from niobium requires several complicated procedures. Commercial production of the element includes methods such as electrolysis of molten potassium fluotantalate, carbother-mic reduction of tantalum oxide, reduction of potassium fluotantalate with sodium, or oxidation of tantalum carbide at 800-900 °C, for example, in scrap from cemented carbides (Hammond 1986, Fichte and Roth-mann 1982). 

Electrochemical anodization of multi-layer AI/Ta/Al thin film compositions was developed to fabrieate regular nanostructures of tantalum oxide (TaiOs). Anodization kinetics, space characteristics of TaaOs nanopillars and electrical properties of Al/TaiOs/Al structures have been studied. Al/Ta/Al thin film compositions were shown to permit formation of regular nanostructured layers appropriate for photonic crystal and nanoelectronic applications. 

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