Chromium oxide, powdered

Oxides. E.s.r. spectra and the temperature dependence of the magnetic susceptibility of chromium oxide powders show differences from the properties found for the bulk material. These differences are proportional to both the increase in surface area and to the concentration of lattice defects. ... 

Chromium oxide is mixed with aluminum powder, placed in a refractory-lined vessel, and ignited with barium peroxide and magnesium powder. The reaction is exothermic and self-sustaining. Chromium metal of 97—99% purity is obtained, the chief impurities being aluminum, iron, and silicon (Table 4). Commercial chromium metal may also be produced from the oxide by reduction with silicon in an electric-arc furnace. 

Arul Dhas N, Koltypin Y, Gedanken A (1997) Sonochemical preparation and characterization of ultrafine chromium oxide and manganese oxide powders. Chem Mater 9(12) 3159—3163... 

Continuous steam distillation, 147, 148 Cooling baths, 61 Cooling curve method, 26 Copper bronze, activated, 193 Copper - chromium oxide catalyst, for aldehyde synthesis, 318, 321 for hydrogenation, 872, 873 hydrogenolysis with, 872J Copper phthalocyanine, 983 Copper powder, 192 Copper sulphate, as desiccant, 40, 41 Cork stoppers, 55 boring of, 56... 

TABLE I X-ray Powder Diffraction Data for Lithium Chromium Oxide, LiCrO20... 

At present, the main industrial catalyst of ammonia oxidation is platinum and its alloys with aluminium and rhodium. Taking into account the deficit and high cost of platinum metals, the dcCTcasing of the consumption and losses of platinum metals is an urgent problem. Therefore, several compositions of complex oxide catalysts have been developed with iron (111), cobalt and chromium oxides as an active component. Complex oxides with perovskite structure are used as new catalysts they provide selective oxidation of ammonia with an yield not less than 90 %. The authors of [33] proposed to use perovskite powders LaMeOj, where Me=Fe, Co, Ni, Cr, Mn, and La,.,Sr,Me03, where Me=Co, Mn and x=0.25-0.75. To prepare these compounds, they used the precipitation by tetraethyl ammonia from diluted nitrate solutions taken at necessary ratios. The powders as prepared are poorly molded as in the form of honeycomb stractures as well as in the form of simple granules. 

Hartl (26) reported attempted nitridations of various metal oxides by means of countercurrent feeding of the oxide powders into an RF nitrogen plasma. Although nitrides were identified by X-ray analysis, their separation was not possible. Table III summarizes the resulting oxynitrides obtained for vanadium, titanium, and chromium. 

Barium Chromite, BaO.CrjOj or Ba(Cr02)2, is a green crystalline powder, obtained by heating together potassium dichromate and barium chloride. By fusing a mixture of barium and chromium oxides in the electric furnace, very hard green crystals of composition Ba0.4Cr20g are obtained, the density of which is 5-4 at 15° C. 

Another common catalyst prepared by coprecipitation is copper-chromium oxide, also known as "copper chromite" or Adkins catalyst.23 This catalyst is prepared by the addition of copper nitrate to a solution of ammonium dichromate in ammonia giving a precipitate copper ammonium dichromate. This precipitate is filtered, dried and then calcined at 650°-800°C, or more commonly, heated with a flame to induce a thermal reaction (Eqn. 13.5). The resulting fine powder is washed with acetic acid and dried to give the copper chromite catalyst.23 A more active catalyst is prepared by adding 10% barium nitrate by weight of copper before precipitation.24,25 Copper chromite catalysts containing calcium and were found to be less effective than those having a barium promoter.25... 

Copper chromite (Lazier catalyst), 156, 975 Copper-Chromium oxide, 157 Copper powder, 157-158 Copper powder-Benzoic acid, 158 Copper salts, 158... 

Typical fillers wood flour, glass fiber, carbon fiber, mica, wollastonite, mineral wool, talc, magnesium hydroxide, graphite, molybdenum sulfide, carbon black, cashew shell particles, alumina, chromium oxide, brass and copper powder, iron particles, steel fiber, ceramic powder, rubber particles, aramid, wollastonite, cellulosic fiber, lignin... 

Chromium Doping. Additions of chromium compounds can be used to produce very fine metal powder grades (<0.5 pm). Chromium oxide is formed during reduction and acts as a grain refiner. Such powders are subsequently carburized to ultrafine WC. Special precautions have to be taken because of the high pyrophoricity of the metal powder. 

An inorganic solid lubricant has been described as a self-lubricating composite comprising a chromium oxide (e.g. chromic oxide, Cr203), a metal binder comprising Cr/Ni or Cr/Co alloy, a metal fluoride, and, optionally, a metal lubricant [60]. A milled powder mix of the composite is deposited onto a substrate, e.g. by plasma spraying. 

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