Cobalt powders preparation

The reduction and nitridation must be carried out in one continuous operation, since the Co powder obtained by reduction of C03O4 is pyrophoric. The cobalt powder prepared from cobalt oxalate cannot be completely converted to nitride under these conditions. 

In comparison, bromobenzene, when heated with commercial nickel powder under the same reaction conditions for 80 h gave only 2.9% biphenyl (8) [77]. Activated cobalt powder, prepared by the Cheng s amalgam-method, behaves similarly to nickel powder and affected the homo-coupling of bromobenzene to biphenyl in 71% yield [77]. 

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

Two general approaches have been used to prepare the cobalt powders. The first method(34,37,42) used 2.3 equivalents of lithium along with naphthalene as an electron carrier in DME to reduce anhydrous cobalt chloride to a dark gray powder, L Use of cobalt bromides or iodides gave a... 

Cobalt(lI) iodide is prepared by heating cobalt powder in a stream of hydrogen iodide at 400 to 450°C ... 

Two discrete carbides have been characterized—C01C and C03C. The former, which has ihe same struciurc as FcjC. has been prepared by reacting cobalt with coal gas at temperatures between 500-800 C. Cu C is formed by the reaction of carbon monoxide at atmospheric pressure on cobalt powder at 225-230rC. 

The nickel, cobalt, and zinc in the reduction end solution are precipitated as metal ammonium double salts after solution evaporation to 500 gm/liter ammonium sulfate. The double salts containing the nickel and cobalt centrifuged from the solution are then dissolved in water. Nickel and cobalt are separated by formation of cobaltic pentammine sulfate solution. The cobaltic pentammine solution is reduced at 350°F under hydrogen at 500 psig to produce cobalt powder. The ammonium sulfate by-product is prepared by stripping out the metal values with hydrogen sulfide. 

Derivation Heating cobalt powder with hydriodic acid anhydrous cobaltous iodide is prepared by heating cobalt in iodine vapor. 

A preliminary x-ray photographic examination of a crystal of the zinc complex showed it to be of excellent quality, and Welssenberg photographs (Okl, Ikl OkO absent for k-2n+l, hOl absent for h+l-2n+l) led to a unique choice of P2j/n as the space group. It was also noted at this time that the nickel and cobalt complexes, prepared in a similar manner, were isoroorphous to the zinc complex. Strict isomorphism (11) was confirmed later by both x-ray powder and single crystal measurements. 

To produce FGM with cobalt varied concentration a mixture was prepared of the following composition 64 % Ti -l- 16 % C -H 20 % Co. The mixture weighing 56 g was placed into a mold. Then cobalt powder was added. Three pellets were obtained with the diameter of 48 mm with various mass ratio of the mixture and cobalt layers 13/56 (0.23) 20/56 (0.36) 28/56 (0.5) correspondently. The relative density of the mixture layer was 0.58 of cobalt layer - 0.65. The SHS-densification was carried out in the reactional mold with the values of the delay time ti = 2 4- 5 sec pressure Pk = 30 MPa and time of exposure t2= 5 4-10 sec. 

Jin Zhang Gao et al, Preparation of ultrafine cobalt powder by chemical reductionin aqueous solution , Chinese Chemical Letters, 21 (6) (2001), 555-558. 

Lu CH, Yeh PY (2002) Microstiuctural development and electrochemical characteristics of lithium cobalt oxide powders prepared by the water-in-oil emulsion process. J Eur Ceram Soc 22 673-679. doi 10.1016/S0955-2219(01)00366-l... 

A slurry of 1 (0.2154g, Sl.Ommol of lithium 0.1840g, 1.4 mmol of naphthalene and 4.5599 g, 14.6 mmol of cobalt iodide 45 ml of THF) was prepared. The metal powder was isolated by filtration under argon and dried in vacuo overnight. The cobalt powder (3.678 g) was slurried in 20 ml of distilled hexanes and treated with 2.72 g (11 mmol) of dichlorodiphenylmethane at room temperature, causing the formation of a green solution. After the mixture was stirred for 48 h, the products were worked up as previously described to give 0.80 g (42%) of tetraphenylethylene. 

A critical issue is the stabiUty of the hydride electrode in the cell environment. A number of hydride formulations have been developed. Table 5 shows hydride materials that are now the focus of attention. Most of these are Misch metal hydrides containing additions of cobalt, aluminum, or manganese. The hydrides are prepared by making melts of the formulations and then grinding to fine powers. The electrodes are prepared by pasting and or pressing the powders into metal screens or felt. The additives are reported to retard the formation of passive oxide films on the hydrides. 

Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. 

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