Uranium carbides preparation

Uranium hexafluoride is prepared by the reaction of fluorine on uranium metal, triuranium octafluoride, uranium pentachloride, or uranium carbide. 

Two uranium carbides are known, the monocarbide, UC, and the dicarbide, UC2. These can be prepared by direct reaction of carbon with molten uranium, or by reaction of carbon monoxide with metallic uranium at elevated temperatures. The scsqutcarbidc, U,Oj, has been found to exist as a stable compound below about 18 ") U and can be produced by heating a mixture of UC and UC2 between 1.250 and 1,800°C. 

Uranium Hexafluoride, Uranic Fluoride, UFg, is the only known compound of hexavalent uranium (with the possible exception of the boride in which the condition of the uranium is not established) which does not contain oxygen. It was first prepared by Ruff and Heinzel-mann by the action of fluorine on uranium pentachloride at —40° C. The action proceed.s as already described (see equation above), and the volatile hexafluoride is distilled off from the tetrafiuoride. The penta-ehloride, Avhen acted upon by dry hydrogen fluoride, yields a compound, UF5.a HF, which breaks up on distillation into the tetra- and hexafluorides, but this method of preparation is less convenient than the preceding one owing to the difficulty of separating the hexafluoride from hydrogen fluoride. Uranium carbide reacts with fluorine in presence of a little chlorine at —70° C., vith formation of the hexafluoride. 

Uranium Carbide, UCj, was first prepared by Moissan by heating together urano-uranic oxide (50 parts) and sugar charcoal (6 parts) in the electric furnace. By employing a current of 900 amperes and 50 volts, the reaction was complete in five minutes, and the fused mass on cooling yielded a lustrous, crystalline solid, of density 11-28 at... 

Uranium carbide UC (UC2 and U2C also exist) has a melting point of about 2300 °C and is an important nuclear fuel for high-temperature reactors. It is prepared by reduction of UO2 with carbon, followed by pressing and sintering. It can also be made by hot pressing of mixtures of uranium metal powder with graphite at 1000 to 1100 °C. A mixed carbide with ThC is manufactured in the form of spheroids by melting. As the product is hydrolyzed on exposure to air, it is coated with a protective carbon layer. 

Uranium carbides may be prepared by reacting uranium with carbon, or uranium dioxide with carbon in vacuum at elevated temperatures, or uranium powder with a hydrocarbon such as methane. 

The very high reactivity of the uranium carbides has been a limitation to their application and a nuisance to those attempting to prepare pure... 

Klaproth reduced the new oxide with carbon at high temperature. His reaction product consisted of gray, lustrous grains, which he regarded as uranium metal. Probably they consisted of uranium carbide to a large extent. The pure metal was prepared in 1842 by E. M. PeHgot in France. He reduced uranium tetrachloride with potassium metal. 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The fuel particles used in these studies were typical pyrolytic carbon-coated thorium-uranium dicarbide, (Th,U)C2, microspheres. The kernels, — 200/i in diameter, were prepared from Th02, U02, and C and converted to the carbide at temperatures below 2200°C., followed by a spheroidization above the melting point, 2450°-2500°C. The bare kernels were coated with a 30-50fi layer of low density (— 1.0 gram/cm.3) buffer pyrolytic carbon, followed by a 40-70/a layer of high density... 

H. Wedemeyer, E. Guenther, Preparation of Uranium-Plutonium Carbide, transl. of KFK-2238 (ORNL-tr-4180), 1974. 

Moissan, Henri. (1852-1907). A Native of Paris, Moissan was a professor at the School of Pharmacy from 1886 to 1900 and at the Sorbonne from 1900 to 1907. At the former institution, he first isolated and liquefied fluorine in 1886 by the electrolysis of potassium acid fluoride in anhydrous hydrogen fluoride. His work with fluorine undoubtedly shortened his life as it did that of many other early experimenters in the field of fluorine chemistry. He won great fame by his development of the electric furnace and pioneered its use in the production of calcium carbide, making acetylene production and use commercially feasible in the preparation of pure metals, such as magnesium, chromium, uranium, tungsten etc. and in the production of many new compounds, e.g., silicides, carbides, and refrac-... 

For reactor fuel, the ternary uranium-plutonium-carbon monocarbide is prepared by reduction of (U, Pu)02 with graphite [FI], by melting a uranium-plutonium alloy with graphite, or by melting separately prepared individual carbides in an electric arc [K2]. Even though at low temperatures UC exists in the stoichiometric composition, the need for excess carbon for the... 

High-purity scandium oxide (i.e., 99.0 to 99.99 wt.% Sc) is an initial raw material used to produce a metallic scandium. After fluorination of the oxide, pure scandium is then prepared by calciothermic reduction of scandium trifluoride (ScFj) with pure calcium metal. The metallic scandium obtained undergoes subsequent refining by vacuum distillation, which ensures a purity of metal at the level 99.99 to 99.999 wt.% Sc. Tentative annual demand for ultrapure metallic scandium for different fields of application is estimated for the near future at 800 to 1000 kg per year. Total annual world production in 2000 of scandium, excluding China, was about 30 kg. Union Carbide and Johnson Matthey, as well as the research company Boulder, are the main manufacturers of scandium products from thortveitite, wastes of uranium, and tungsten production. 

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