Cobalt, metaUic

Syntheses from Dry Metals and Salts. Only metaUic nickel and iron react direcdy with CO at moderate pressure and temperatures to form metal carbonyls. A report has claimed the synthesis of Co2(CO)g in 99% yield from cobalt metal and CO at high temperatures and pressures (91,92). The CO has to be absolutely free of oxygen and carbon dioxide or the yield is drastically reduced. Two patents report the formation of carbonyls from molybdenum and tungsten metal (93,94). Ruthenium and osmium do not react with CO even under drastic conditions (95,96). 

MetaUic cobalt dissolves readily in dilute H2SO4, HCl, or HNO to form cobaltous salts (see also Cobalt compounds). Like iron, cobalt is passivated by strong oxidizing agents, such as dichromates and HNO, and cobalt is slowly attacked by NH OH and NaOH. 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

Toniolo, J.C., Taldmi, A.S., Beigmann, C.R Nanostructured cobalt oxides (C03O4 and CoO) and metaUic Co powders synthesized by the solution combustion method. Mater. Res. Bull. 45, 672-676 (2010)... 

In 2004, void formation in spherical samples was rediscovered at the nanolevel and discussed in [4-6]. HoUow nanosheUs of cobalt and iron oxides and sulfides have been obtained by means of reaction of metaUic nanopowders with oxygen or sulfur. Contrary to [2, 3], these results have been explained by the Frenkel effect - out-diffusion of metal through the formation of a spherical layer of the compound is faster than in-diffusion of oxygen or sulfur through the same phase. This inequahty of fluxes generates the inward flux of vacancies, meeting inside and forming the void in the internal part of the system. 

Pyrolysis of acetylene on the surface of MCM-41 silicas containing metaUic catalysts has been studied. Application of matrices with the supported metals as catalysts enabled us to attain rather high yields of carbon nanostructures (20-30% of the process product). The electron microscopy data provided evidence for formation of nanotubes with an external diameter of 42-84 nm in the case of the cobalt catalyst and 14-200 nm in the case of the iron catalyst Formation of carbon fibers with diameters in the interval 80-110 nm for the nickel catalyst was also observed. In the absence of a catalyst on such matrices small yields (up to 2%) of carbon nanotubes were attained. 

Pita, M., Abad, J. M., Vaz-Dominguez, C., Briones, C., Mateo-Marti, E., Martin-Gago, J. A., Puerto Morales, M., and Fernandez, V. M. 2008. Synthesis of cobalt ferrite core/metaUic shell nanoparticles for the development of a specific PNA/DNA biosensor. J. Colloid Interface Sci. 321 484-492. 

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