Chromium carbides preparation

Chromium Carbide. the chromium carbide having the highest carbon level, is used as an additive in the preparation of cobalt or... 

Chromium carbide can be best prepared from pure chromic oxide [1308-38-9] (see Chromium compounds). Compacts containing 74 wt %... 

Chromium carbide is important in powder preparations designed for thermal spray apphcations of corrosion and wear-resistant coatings on tool and machine parts. Lower carbon carbides of chromium are important in hardfacing tods and electrodes for weld-apphed ovedays on machine wear surfaces. However, these carbides are usually formed in situ from Cr and C in the rod and not added as preformed carbides. The properties of Ci2C2 are hsted in Table 2. 

Chromium carbide can be best prepared from pure chromic oxide [1308-38-9], Cr203 (see Chromium compounds). Compacts containing 74 wt % Cr203 and 26 wt % carbon black can be heated in carbon-tube furnaces at 1600°C in the presence of hydrogen, giving a carbide containing 13—13.3 wt % total C and 0.1—0.3 wt % free C. 

The preparation of TiC, VC, NbC, TaC, M02C, WC, and the chromium carbides are important technical processes for the production of carbide powders for hardmetals. Generally, the carbides are prepared by the reduction of oxides with carbon only M02C and WC are manufactured by reaction of the metal powders with graphite or carbon black. 

The catalyst preparation procedure starting with the adsorption of a metal hydroxide followed by its reduction in a stream of H2 at 600 C and a further activation step in acetonitrile at 1,000°C was expanded to all transition metals of the first row. Catalysts for O2 reduction were obtained only with Cr, Fe, and Co. Cr203/C, Fe/C, and Co/C were detected after the reduction step in H2, while Co, Fe3C, and a chromium carbide-nitride (Cr6.2 C3 5 N0.3/C) were detected in the catalyst. The nominal loading of all metals was 10 wt%. Catalytic activity decreased as Cr > Fe > Co. Tests in fuel cells indicated that the Cr-based catalyst was not stable, while Fe and Co-based catalysts were stable (see Section 4 for details). 

Numerous attempts to obtain pure chromium were unsuccessful. L. Vauquelin himself tried to prepare it but most likely it was chromium carbide that he obtained. 

In MAFBS experiments to produce molybdenum carbide, molybdenum and carbon black powders were mixed in a 2 1 molar ratio. Five grams of this mixture were added to the quartz tube and fluidized with argon. Visible heating effects in these experiments were similar to those in experiments to prepare chromium carbide. 

Cr3C2 powder is prepared by the reaction of chromium oxide (Cr203) with carbon up to 16(KK]) in hydrogen if the temperature is kq>t below 1300, Cr7C3 is obtained. An oxygen free-carbide can be obtained by the carburization of the chromium metal. Chromium carbide coatings are d osited by CVD, reactive evaporation, and sputtering (see Chs. 14 and 15). 

Thomberg, T., Kurig, H., Janes, A., and Lust, E. Mesoporous carbide-derived carbons prepared from different chromium carbides. Microporous and Mesoporous Materials, 141, 88-93, 2011. 

The submitters employed an aqueous 1.64Jtf solution of chromium(II) perchlorate which was prepared by stirring a mixture of 5.7 g. of pure chromium metal pellets (United Mineral and Chemical Corporation, 129 Hudson St., New York, 10013) with 60 ml. of aqueous 20% perchloric acid under a nitrogen atmosphere at 30° for 12 hours.2,3 The rate of dissolution of the chromium metal is increased if the metal is washed successively with concentrated hydrochloric acid and with water just before it is added to the perchloric acid. The checkers employed aqueous 0.519J/ chromium(II) perchlorate solution which was prepared in a comparable manner with chromium metal obtained from the Mining and Metals Division, Union Carbide Corporation. The deep blue solution of chro-mium(ll) perchlorate is transferred to a storage vessel with a... 

Union Carbide (95, 96) developed chromium catalysts that need activation by aluminum alkyls, but which have the advantage that molecular weight can be controlled with hydrogen, as in the case of the titanium-based catalysts. To prepare the catalysts, organosilanols are combined with chromium trioxide to afford silylchromate. The silylchromate is then deposited on a silica support and activated with an aluminum alkyl (see Fig. 13). 

Pentachromium Dicarbide, CrjGg, can be prepared in quantity by melting a mixture of chromium and a finely powdered chromium-carbon alloy containing-11-16 per cent, of carbon in a magnesia crucible at 1800° to 1850° C. After repeatedly washing the product vdth 2N hydrochloric acid until no more chromium dissolves, the carbide, CrjCj, is obtained practically pure. It forms silvery crystals, of density 6-915 at 24-8° C. It is not attacked by aqua regia, and melts without appreciable decomposition at 1665° C. 

Alloys of chromium and silicon are readily obtained by heating chromium sesquioxide with excess of silicon at 11 white heat, or with silicon carbide, or silicon carbide and carbon, in the electric furnace or by strongly heating chromium sesquioxide, silica, and aluminium. From these alloys several definite silicides have been isolated, which are usually grey in colour, hard and brittle, and very resistant to acids, except hydrofluoric acid, which readily, decomposes them. The silicides, CrjSi, CrjSi, CrgSia, and CrSij, have been obtained in a state of comparative purity by special methods of preparation. ... 

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-... 

A competitor of Phillips catalyst, based on chromium oxide supported on silica, is the Union Carbide catalyst, which is prepared by the reaction of chromocene with silica. When chromocene, [Cp2Cr ], reacts with SiO2-(800)> it gives [(=SiO)Cr(Cp)] according to mass balance analysis (Scheme 42 and Table 12), and this surface complex is highly active in ethylene polymerization. ... 

Cyclopentadienyl tricarbonyl hydrides of chromium, molybdenum, and tungsten can be prepared by reaction of Institute for Inorganic Chemistry, The University, Munich, Germany, t Union Carbide Chemicals Company, South Charleston, W.Va. 

A new monoboride phase (CrB) has been detected in alloys prepared at relatively low temperatures together with a chromium-rich phase which has not yet been characterized. Investigations in the Cr-B-C system show that mutual solubility of the Cr carbides and borides is insignificant up to 1000 °C. Carbon/boron substitution in Mn23Cg extends almost to MnaaCgBg. 

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