Carbon in niobium

The solubility of carbon in niobium is very low at 1200°C it amounts to 13 / g/g and at 2000 C to 0.1 at.% (130 Mg/g). During cooling of carbon containing systems, precipitates of Nb2C and/or Nb2C2 are formed. 

At temperatures above 1500°C, the resistivity increases linearly with the 

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THE DETERMINATION OF CARBON IN NIOBIUM, TANTALUM, MOLYBDENUM AND TUNGSTEN... 

For tantalum the method of analysis is identical to the one used for the determination of carbon in niobium except that no flux is required. 

Oral lath et al. (25) confirm the usefulness of the technique described by Kraft and Kahles (24) for the analysis of zirconium (2.5 to 3 fold amount of iron flux, heating at 1450°C under argon, gradual forcing out the argon with oxygen) to analyse carbon in. niobium and niobium alloys. In this case an amount of iron flux equal to the amount of niobium sample is sufficient. 

The conditions for the determination of carbon in niobium and tantalum are similar to those for zirconium and zircaloy. Experimental details are... 

The determination of carbon in niobium, molybdenum, tantalum and tungsten... 

Niobium pentoxide can be reduced with carbon in a two-step process, called the Balke process. Formation of the carbide is the first step. The oxide is mixed with the stoichiometric amount of lamp black, placed in a carbon cmcible, and heated in vacuum to 1800°C ... 

Having established the feasibility of niobium metal production by the carbothermic reduction of niobium pentoxide under temperature and pressure conditions readily attainable in the laboratory and in industry, the principles of efficient process execution may now be examined. In a high-temperature vacuum furnace operation, the quantity of gas that is to be pumped off can influence the choice of the vacuum process. When the reduction of niobium pentoxide with either carbon or niobium carbide is attempted according to the following overall equations ... 

Oxygen and carbon have substantial solid solubilities in niobium at the temperatures normally required for reduction. As the activity coefficients of both carbon and oxygen in niobium are low, their retention in the niobium metal produced by the carbothermic reduction of niobium oxide is expected. It is, however, possible (as explained later) to remove these residual impurities by extending the pyrovacuum treatment to still higher temperatures and lower pressures. 

Balke A process for making niobium by reducing niobium pentoxide with carbon in a carbon crucible, in vacuo, at 1,800°C. 

Niobium was prepared in the metallic state for the first time by Blomstrand in 1866, later by Moissan, and still later, by Goldschmidt. While Blomstrand reduced niobium chloride with hydrogen to form niobium, Moissan and Goldschmidt reduced the oxide with carbon (in an electrical furnace) and aluminum powder, respectively. 

Niobium Pentabromide, NbBrs.—This is the only bromine compound of niobium hitherto prepared. It is obtained by the action of bromine vapour on the coarsely powdered metal,2 or on a mixture of niobium pentoxide and carbon in the absence of air.2 In the latter case some of the oxybromide is also formed. Niobium pentabromide is a fine, purple-red powder, very similar to red phosphorus in appearance. The fused substance forms garnet-red prisms. On being strongly heated it becomes yellow, and volatilises. It melts at about 150° C., and distils undecomposed in an inert atmosphere at about 270° C. It can be distilled unchanged in an atmosphere of nitrogen or carbon dioxide. It is very hygroscopic, hydrolyses rapidly in damp air, and is decomposed by water with a hissing noise and considerable evolution of heat into niobie add and hydrobromic add. It is soluble in absolute alcohol and in dry ethyl bromide. 

Oxalo-niobates or niobo-oxalates correspond to the vanado-oxalates, and contain both oxalic acid and niobic add radicals in the complex anion. The only known series possesses the general formula 3R aO. Nb 205.6C203.a H20, where R stands for an alkali metal. The sodium, potassium and rubidium salts are prepared by fusing one molecular proportion of niobium pentoxide with three molecular proportions of the alkali carbonate in a platinum crucible. The aqueous extract of the melt jjs poured into hot oxalic add solution concentration and cooling, or addition of alcohol or acetone, then brings about precipitation of the complex salt. Comparison of the dectrical conductivity measurements of solutions of the alkali oxalo-niobates with those of the alkali hydrogen oxalates determined under the same conditions indicates that the oxalo-niobates are hydrolysed in aqueous solution, and that their anions contain a complex oxalo-niobic acid radical.6... 

Martynenko, V. M., and Borovinskaya, I. P., Some characteristic features of the combustion in system niobium-carbon. In Combustion Processes in Chemical Engineering and Metallurgy (Russ.) (A. G. Merzhanov, ed.). USSR Academy of Science, Chemogolovka, Russia, 1975, p. 127. 

Fine-grain, carbon-manganese steels of the same type and with identical properties are standardized in France and Italy — A52 and 20 M5, respectively. The Swedish and British equivalents have somewhat lower yield strengths, and in these countries there is more interest in niobium-treated, fine-grain, high-strength steel. 

Bra] Brandis, H., Preisendanz, H., Sehueler, R, The Influenee of Alloying Elements Titanium, Vanadium and Niobium on the Aetivity of Carbon in Fe-X-C Alloys in the Temperature Range from 900 to 1100°C (in German), Thyssen Edelst. Techn. Ber., 7(1), 92—104 (1981) (Experimental, Thermodyn., 32)... 

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