Tantalum spinning

Gold can be used only in very small portions or very thin coatings because of its cost. Most of the applications for wliich it was used in the past have now been accomplished with tantalum at a much lower cost. A gold/ platinum/rhodium alloy is used in the manufacture of rayon-spinning jets in the production of rayon fibers. This alloy presents the combination of strength, corrosion resistance and abrasion resistance necessary to prevent changes in hole dimensions. 

Spinning Tantalum can be formed by all conventional spinning techniques, provided a lubricant such as tallow is employed, and can be spun into configurations which cannot be produced by other forming methods. 

Niobium- and tantalum-containing mesoporous molecular sieves MCM-41 have been studied by X-ray powder diffraction, 29Si MAS NMR, electron spin resonance, nitrogen adsorption and UV-Vis spectroscopy and compared with niobium- and tantalum-containing silicalite-1. The results of the physical characterization indicate that it is possible to prepare niobium- and tantalum-containing MCM-41 and silicalite-1, where isolated Nb(V) or Ta(V) species are connected to framework defect sites via formation of Nb-O-Si and Ta-O-Si bonds. The results of this study allow the preparation of microporous and mesoporous molecular sieves with remarkable redox properties (as revealed by ESR), making them potential catalysts for oxidation reactions. 

Both metals are active in NMR (spin 9/2 for Nb, 7/2 for Ta) and have high sensitivities, but their major drawbacks are their large quadrupole moments that often result in broad signals (several kHz) in low symmetry environments, and thus application of NMR remains limited, especially for tantalum. Ta is a nucleus with interesting characteristics... 

Attempts to prepare protactinium pentanitrate by reacting penta-halides with liquid dinotrogen pentoxide have resulted in the formation of HPalNOglfl, possibly as a result of traces of anhydrous nitric acid present in the N Os 49). The presence of the jiroton has not been confirmed by electron spin resonance studies, but infrared results have shown that all the nitrate is covalently bound and vibrations associated with the nitronium and nitrosonium cations were not observed. Niobium and tantalum pentahalides react under similar conditions to form the anhydrous oxytrinitrates, M 0(N0g)3 20, 87). 

The aged solution is forced by a pump through a spinning jet or spinneret. This consists of a cap made of a chemically inert metal, such as tantalum or platinum or platinum-rhodium alloy, which contains a number of small holes usually between 0 05 and O-l mm in diameter (see Fig. 6.1). The spinning mixture is extruded through these holes into a medium which causes it to solidify or coagulate. 

The tantalum and niobium tubes are readily trimmed and opened after use with the spin-cutter of the sort used for cutting copper pipe. A tapered flaring tool is also helpful during the construction of apparatus. The tantalum tubing can often be reused if contamination from contents or outgassing of the jacket is not serious. Ductility or softness (low yield stress) is a good indication of purity. 

Monomeric species M OR-tert)x have been characterized for titanium, vanadium, chromium, zirconium, and hafnium (x = 4) and for niobium and tantalum (x == 5). With chromium it was found that limiting Cr(III) to coordination number 4 in the dimeric Cr2(OBu )e caused instability and a remarkable facility toward valency disproportionation or oxidation to the stable quadricovalent Cr(OBu )4 (8, 9). In contrast, molybdenum formed a stable dimeric tri-tert-butoxide (Bu O)3Mo=Mo-(OBu )3 which is diamagnetic and presumably bound by a metal-metal triple bond (10, II). Yet another interesting feature of chromium is the synthesis of a stable diamagnetic nitrosyl Cr(NO) (OBu )3 in which the nitric oxide is believed to act as a three-electron donor with formation of a four-coordinated low spin chromium (II) compound (12). The insta-bihty of Cr2(OBu )e and the stability of both Cr(NO) (OBu )3 and Cr(OBu )4 must result from the steric effects of the tertiary butoxo groups since the less bulky normal alkoxo groups form very stable polymeric [Cr(OR)3]a. compounds in which the Cr(III) has its usual coordination number of 6 (octahedral). 

Fig. 3. The ionization energy of the 4f shell in oxides (empty cirdes), fluorides (squares) and other compounds (filled circles) of lanthanides, hafnium and tantalum. The effects of spin-pairing energy are compared with values of I derived from the calculated uncorrected optical electronegativities (116) for M(IV) and given as full curves appropriate for the ionization of M III). The dashed lines connect the iso-electronic 4f and 4f systems with differing oxidation state.

The absorption of water by polymers is especially suited to the development of a capacitive humidity sensor based on the high dielectric constant of water, since capacitance depends on the area, the thickness, and the dielectric constant of a dielectric. Uptake of water causes an increase in the dielectric constant followed by an increase in capacitance. Polyimide is a suitable sensitive material, but so are certain inorganic ceramics such as AI2O3 [142] and low-density Ta205, which change their capacitance with the formation of water dipoles. Low-density Ta20s layers can be formed by anodic oxidation of sputtered tantalum films, whereas polyimide films are deposited by spin coating and subsequent polymerization. 

The spinnerets are made of various materials depending on the spinning solutions. Precious metal alloys of gold, platinum, iridium, as well as rhodium, tantalum, and glass are used. The shape and size of the boreholes differ. For the production of viscose fibers, spinnerets have 30,000 to 90,000 capillaries. Acrylic fibers are spun according to the wet-spinning method with 40,000 to 150,000 holes per spinneret (Rogowin, 1982). 

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