Powder cobalt

Pressure-acid leaching was used to extract cobalt from Blackbird mine ores before its closing in 1974. The result was a very fine cobalt powder which was subjected to a seeding process to produce cobalt granules. Leaching methods are also used in the refinement of lateritic ores. 

Cobalt(II) oxalate [814-89-1], C0C2O4, is a pink to white crystalline material that absorbs moisture to form the dihydrate. It precipitates as the tetrahydrate on reaction of cobalt salt solutions and oxaUc acid or alkaline oxalates. The material is insoluble in water, but dissolves in acid, ammonium salt solutions, and ammonia solution. It is used in the production of cobalt powders for metallurgy and catalysis, and is a stabilizer for hydrogen cyanide. 

Cobalt compounds can be classified as relatively nontoxic (33). There have been few health problems associated with workplace exposure to cobalt. The primary workplace problems from cobalt exposure are fibrosis, also known as hard metal disease (34,35), asthma, and dermatitis (36). Finely powdered cobalt can cause siUcosis. There is Htfle evidence to suggest that cobalt is a carcinogen in animals and no epidemiological evidence of carcinogenesis in humans. The LD q (rat) for cobalt powder is 1500 mg/kg. The oral LD q (rat) for cobalt(II) acetate, chloride, nitrate, oxide, and sulfate are 194, 133, 198, 1700, 5000, and 279 mg/kg, respectively the intraperitoneal LD q (rat) for cobalt(III) oxide is 5000 mg/kg (37). 

Cobalt salts are used as activators for catalysts, fuel cells (qv), and batteries. Thermal decomposition of cobalt oxalate is used in the production of cobalt powder. Cobalt compounds have been used as selective absorbers for oxygen, in electrostatographic toners, as fluoridating agents, and in molecular sieves. Cobalt ethyUiexanoate and cobalt naphthenate are used as accelerators with methyl ethyl ketone peroxide for the room temperature cure of polyester resins. 

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. 

Cobalt represents an interesting contrast to the many activated metal powders generated by reduction of metal salts. As will be seen, the cobalt powders are highly reactive with regard to several different types of reactions. However, in contrast to the vast majority of metals studied to date, it shows limited reactivity toward oxidative addition with carbon halogen bonds. 

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 has been used as a Fischer-Tropsch catalyst in a variety of forms(80). Thus it was not surprising to see that both active forms of cobalt powders were moderate Fischer-Tropsch catalysts. Reacting synthesis... 

The highly oxophilic nature of the cobalt powder was readily demonstrated by its reaction with nitrobenzene at room temperature. Reductive coupling was quickly effected by 2 to give azo- and azoxy derivatives. Nitrobenzene reacted with 2 to give azobenzene in yields up to 37%. In some cases small amounts of azoxybenzene were also formed. With 1,4-diiodonitrobenzene, 2 reacted to give low yields of 4,4-diiodoazoxy-benzene and 4,4-diiodoazobenzene. 

The application of electrospray ionization (ESI) to macromolecules was first described by Yamashita and Fenn in 1984, and he later applied this technique to the study of proteins in 1988. In ESI, charged droplets of protein were produced and the solvent was stripped away, leaving only the free protein ion. In 1987, Tanaka demonstrated that laser pnlses from a low-energy nitrogen laser could be used to ionize proteins from a surface. As described in a paper presented during the Second Japan-China Joint Symposium on Mass Spectrometry, proteins are desorbed from a glycerol matrix containing cobalt powder. The cobalt powder was necessary to increase absorption of the laser photons. ... 

In the occupational setting, exposure to cobalt alone occurs primarily in the production of cobalt powders. With other industrial exposures, such as hard metal exposure, additional... 

The solution on concentration and cooling forms crystals of hexahydrate which on heating with SOCI2 dehydrates to anhydrous cobalt(II) chloride. Alternatively, the hexahydrate may be converted to anhydrous C0CI2 by dehydration in a stream of hydrogen chloride and dried in vacuum at 100-150°C. The anhydrous compound also may be obtained by passing chlorine over cobalt powder. 

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

Cobalt(lI) iodide also may be made by heating cobalt powder with iodine vapor. 

Table 9.2.4 Chemical Analysis of Two Cobalt Powders Obtained from the Same Parent Hydroxide by Solid-Gas Reduction and by the Polyol Process (Main Impurities/ Cobalt Ratios in ppm by Weight)...

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. 

SiC-coated or uncoated MWCNTs are dispersed in isopropylalcohol (IPA) using ultrasonic vibration for 5 min. Then the SiC-coated or uncoated MWCNTs are mixed with fine WC and cobalt powders (10 wt% cobalt) in IPA using plastic balls (10-20 mm in diameter) for 5 h. After ball milling, the IPA solution is evaporated by stirring using an electric heater and then dried at... 

Then a mixture of diamond and cobalt powders was placed into the cell and subjected to pressure and temperature. Liquid cobalt that wetts diamond is pulled out of the compact if the volume occupied by cobalt somewhat exceeds the total volume of pores which remained after shrinkage of diamond powder. When liquid metal is in contact with a graphite heater, the current flow at first increases due to a total drop of the system electric resistance and then decreases because of diamond formation in the heater. In this case, the shrinkage value corresponds to the volume of cobalt in the powder. 

TetramethyIisoindole (6 g, 34.6 mmole) and cobalt powder (30 g, 0.51 mole) are mixed and loaded into a Carius tube (4 X 35 cm volume about 450 mL). After it is evacuated and sealed, the tube is placed in a shielded oven preheated to 390° and heated at this temperature for 4 hours. After the tube is cooled, the dark-blue (or black) powder is placed in a Soxhlet extractor and extracted with pentane (300 mL) until a red-brown impurity is removed (about 24 hours). The pentane is replaced by toluene (300 mL), and extraction is continued until the extract (initially green) is colorless (about 8 hr). Finally, pyridine (300 mL) is used to extract (Soxhlet extractor) the porphine, which requires about 10 hours. The pyridine solution is concentrated to 20 mL, and 100 mL of hexane is added. The precipitate is collected, washed with hexane, and dried overnight in vacuum at 60°, to give [octamethyltetrabenzoporphinato-(2-)] cobalt(II). Yield 2-3 g (35-55%). Anal. Calcd. for C44H36N4Co C, 77.79 H, 530 N, 8.24. Found C, 77.87 H, 5.40 N, 8.48. 

DFG MAK DFG TRK 0.5 mg/m calculated as cobalt in that portion of dust that can possibly be inhaled in the production of cobalt powder and catalysts hard metal (mngsten carbide) and magnet production (processing of powder, machine pressing, and mechanical processing of unsintered articles) other cobalt alloys and compounds 0.1 mg/m calculated as cobalt in that portion of dust that can possibly be... 

The processing of nickel oxide ores is illustrated by the sulfuric acid leaching of nickeliferous laterites and the precipitation of high-purity nickel and cobalt powder by reaction with hydrogen gas giving ammonium sulfate as by-product. This process is in use at Moa Bay, Cuba. 

The oxidized solution pH is adjusted to 2.5 with sulfuric acid. The nickel ammonium sulfate double salt is precipitated, filtered, dissolved in aqueous ammonia solution, and returned to the main leach circuit. The filtrate is evaporated to increase ammonium sulfate and cobalt concentration, and H2SO4 is added to remove the residual nickel. The filter residue is returned to the oxidation feed tanks. Cobalt powder is added to the pure cobalt solution to convert the cobaltic to cobaltous, in a process similar to the nickel reduction with hydrogen gas. 

Fig. 14. Freeport Nickel Company, simplified flow diagram for production of nickel and cobalt powders from laterites. Evans (ElO).

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. 

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