Tantalum sampling tubes

Samples were taken in tantalum sampling tubes having a porous tantalum filter (35 u pore) at the end. An explanation of the sampling technique has been reported previously(10). The melts were contained in tantalum crucibles and equilibrated by stirring for 1-1/2 hours between samples. The temperatures were measured by means of a calibrated chrome1-alumel thermocouple with an estimated accuracy of 1°C. 

Halliday et al. [396] have described a simple rapid graphite furnace method for the determination of lead in amounts down to 1 xg/l in polluted seawater. The filtered seawater is diluted with an equal volume of deionised water, ammonium nitrate added as a matrix modifier, and aliquots of the solution injected into a tantalum-coated graphite tube in an HGA-2200 furnace atomiser. The method eliminates the interference normally attributable to the ions commonly present in seawater. The results obtained on samples from the Firth of Forth (Scotland, UK) were in good agreement with values determined by anodic stripping voltammetry. 

An alternate method for quickly obtaining smaller (1-g) batches of TaS, powder is to place tantalum powder (-60 mesh) in a 10-12 mm (inside diameter fused) quartz tube, 10 cm long, with a stoichiometric quantity of sulfur. This mixture will react completely in a relatively short while (2-3 days) at 450°. The sample may then be heated uniformly to 850-900° as described for the larger batch. 

Hulliger and Ott (1977) reported the anti-Th3P4 structure type for Eu4TeSb2, a = 0.9814 from X-ray powder diffraction. The sample was placed in tantalum or molybdenum crucible and heated in quartz tube below 1273 K. 

The CVD reactor consists of a vitreous silica tube of about 20 cm in diameter (8") and a height of 30.5 cm (1 ft). The filament was made from tantalum wire with 0.5 mm diameter and attached to water-cooled copper electrodes. Heat treatment in a methane atmosphere produces a thin layer of tantalum carbide that protects the sample from contamination with metallic tantalum. A gas-leaking unit allows the introduction of various gases and their mixtures into the reaction chamber under controlled pressure. Before introducing or changing the gas the unit s internal pressure was reduced by a mechanical pump to about 0.1 Pa. 

A colorimetric method has been proposed by Meimberg1 for the estimation of columbium. Most of the tantalum is removed as the fluotantalate, then the columbium is reduced with tin in a colorimetric tube. The amount of columbium is determined by comparison with a fresh standard solution. For samples of 10 grams an accuracy of 0.01 per cent is claimed. 

The performance of coated tubes may be very bad, when organic soivent extracts are used, like the extract of diethyidithiocarbamate in toluene (Kubasik and Volosin, 1973). In the latter case, nearly double the sensitivity was obtained by inserting a tantalum foil into the tube to avoid soaking the graphite with toluene. Drying of aqueous Pd matrix modifier solution on the tube wall prevented soaking of coated tubes with di-isopropylketone sample solution (Collett and Jones, 1991). 

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