Niobium metal powder

Rare earth metals, as well as alkali earth metals, can be used as oxygen getters in the purification of tantalum powder. Osaku and Komukai [608] developed a method for the production of tantalum and niobium metal powder by a two-step reduction of their oxides. The second step was aimed at reducing the oxygen content and was performed by thermal treatment with the addition of rare metals. The powder obtained by the described method is uniform, had a low oxygen level and was suitable for application in the manufacturing of tantalum capacitors. 

Also, the pentoxide may be produced by igniting niobium metal powder, niobium carbide, or niobium fluoride in oxygen. 

Drying is in a conventional vacuum drying oven at 40 C for 10 hr, although niobium metal powder produced by this route is sufficiently coarse for it to be oxidized only with difficulty. Drying can therefore, if necessary, be done in an ordinary air oven at 80°C. 

Niobium metal powder has been produced by the reduction of the relatively inert black solid, niobium trichloride, in a current of hydrogen, i.e. 

Kilogram batches of the chloride are reduced in molybdenum trays, it being rather important to distribute the powder in thin layers in the trays. A silica tube furnace is used at a temperature of 800°C to 1000°C. A plant consisting of six tubes each 12 ft long by 6 in. diameter, filled with molybdenum trays, has an output of 25 kg of niobium metal powder per week. An 80 per cent yield is then obtained in 60 to 70 hr. 

The higher chlorides are volatile and reduce directly in hydrogen, depositing both niobium metal and niobium trichloride on the walls of the furnace tube, away from the reaction trays. Besides the inconvenience of this mass transfer effect, the niobium metal powder deposited from reduction of the gaseous higher chlorides tends to be very finely divided and therefore pyrophoric on exposure to air. Nevertheless, the product of the trichloride reduction reaction, has been handled satisfactorily, and has given ductile massive metal on sintering. 

Preparation of the solutions was similar to that of niobium-containing solutions, i.e. by dissolving tantalum metal powder in hydrofluoric acid, HF, at a concentration of about 40% weight. 

In order to produce coarse-grained tantalum or niobium powder it is recommended to perform the reduction of molten K2TaF7 or K2NbF7 with sodium or potassium in the presence of tantalum or niobium metal particles, which are added to aid nucleation [582]. It is reported that tantalum powder with an average particle size of 2.7-4.2 pm was obtained at a yield of 90.1-94%. 

Powdered niobium metal, 20.0 g. (—200 mesh), and tin(II) fluoride, 52.0 g. (40 mesh),t are mixed in a molybdenum crucible in an Inconel- or nickel-pipe reactor approximately 3 in. in diameter and 10 in. long and heated to 400-500°C. in a stream of dry nitrogen. The niobium(V) fluoride volatilizes from the reaction mixture and condenses on the water-cooled lid of the reactor, which leaves metallic tin in the crucible. The yield of niobium(V) fluoride is 21.1 g., or 95% of theoretical. A very small amount of blue niobium oxyfluoride (composition of variable oxygen and fluorine content) often forms as an impurity because of the presence of minute amounts of oxygen. Anal. Calcd. for NbFs Nb, 49.44 F, 50.56. Found Nb, 49.43 F, 50.2. 

M. R. Jackson, Ductile low-density alloys based on niobium, Tungsten and Refractory Metals-1994, eds. A. Bose and R. J. Dowding (Metals Powder Industries Federation, New... 

Niobium metal, either as a powder or as a solid, can be readily chlorinated in a Cl g stream. The reaction is best carried out in a... 

The author has explored somewhat casually the qualifications of certain tantalum and niobium (cdumbium) powder samples and found that they reacted with barium chromate without the addition of a more active oxidizer. This is an encouraging feature pointing toward the potential usefulness of more of the very heavy and pyro-chemically active metals, if only scientific research can provide us with means for defining the surface properties of these metals so that they can be made rcproducibly to pyrotechnic requirements. 

The anode bodies of tantalum, aluminum, and most recently niobium capacitors are made of highly porous metals. These bodies are obtained either by sintering fine metal powders or electrochemical etching of thin foils. A thin dielectric layer is then electrochemically grown on the metal surface. Due to the porous structure of the anode bodies, the cathode polymer must be able to penetrate deep into the pores and coat aU internal surfaces in order to utilize the full, potential capacitance of the anode. 

Vanadium (V) (Aldrich Chemicals, -325 mesh, 99.5% purity), niobium (Nb) (Strem Chemicals, -325 mesh, 99.8% purity), and tantalum (Ta) (Aldrich Chemical, -325 mesh, 99.9% purity) powders were used as the reactants in this study. Metal powders were pressed into cylindrical specimens with a diameter of 7 mm and a height of 12.5 mm. In order to prepare test samples with different porosities, the powder compacts were formed with a packing density between 45% and 60% relative to the theoretical maximum density (TMD). For the study of the effect of nitride dilution on the SHS reaction, VN and NbN were employed as the diluents to add into the V and Nb powder compacts, respectively. The diluent content ranged from 5% to 30% by weight of the total powder mixture. No TaN dilution was applied for the Ta powder compact, because of no anticipation of melting upon considerably high melting points of Ta (2996 °C) and TaN (3090 C). 

After the sodium reaction has subsided, the alcohol fire is suppressed by by means of the reactor lid. The alcohol is allowed as much as 24 hr to completely penetrate the cake and after decanting the liquid away the solid contents are broken in the reactor by means of a chisel and emptied carefully onto a steel tray. The cake is then cracked by hand on the tray and fed to a roll-crusher. The powdered mixture of niobium metal and alkali metal fluorides is next leached with water. The first leach with several hundred litres of water can be in a rotating inclined vessel, carried out as a simple batch operation, to remove most of the potassium fluoride and a proportion of sodium fluoride, relatively quickly. Owing to the fairly low solubility... 

Tantalum metal powder is produced by the sodium reduction of potassium heptafluotantalate (K2Tap7) in a similar manner to the niobium reaction.23 The particular open reaction technique for niobium was in fact based upon that for tantalum in some details. 

NbC powder is prepared by the reaction of niobium oxide with carbon at 1700°C in hydrogen. The reaction of niobium metal or niobium hydride with carbon under vacuum is also used. NbC coatings are deposited by CVD, reactive evaporation, or sputtering (see Chs. 14 and 15). 

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