Cobalt appearance

Spectra of the mixed spinels are interpretable in terms of X-ray diffraction studies of the same samples by Azdroff (16). Cobalt appears to be in the divalent condition, based upon the location of the principal maximum. Manganese appears in a higher valence state. The extended fine structure, which is supposed to be determined by the lattice, appears identical for all the spectra of Figs. 14 and 15 which are of truly cubic spinels, namely CosOi,... 

The comparison of the various cobalt-complexes discloses the limitations of the usefulness of the oxidation number. In the Co(I)-R-complexes the cobalt appears to have a smaller positive net charge — if not a small negative net charge — than cobalt in the cobalt(0)-carbonyl complexes. 

In these compounds the maximum co-ordination, whether of tri-valent or tetravalent cobalt, appears to be six, as in the case of the simpler cobalt-ammines. 

Yet, the structure of this Co-Mo-S phase remains to be determined. A model system, prepared by impregnating a MoS2 crystal with a dilute solution of cobalt ions, such that the model contains only ppm-levels of cobalt, appears to have the same Mossbauer spectrum as the Co-Mo-S phase. It has the same isomer shift (characteristic of the oxidation state), recoil-free fraction (characteristic of lattice vibrations), and almost the same quadrupole splitting (characteristic of symmetry) at all temperatures between 4 and 600 K [78], Thus, the cobalt species in the... 

Recent work on the rapid electro-deposition of cobalt appears to have stimulated further research into the possibilities of increasing the rapidity of nickel deposition, and it would appear that the subject has not yet been exhausted. Watts recommends hot solutions (c. 70° C.) of the composition mentioned above and a current density of 200 to 300 amperes per square foot (22 to 33 per square decimetre). He claims that, under these conditions, the same amount of metal is deposited in five minutes as requires one and a half hours in the rapid solutions nowr in use at 10 amperes per square foot. ... 

These data, coupled with the fact that the epoxide selectivity is not greatly influenced by the presence of cobalt, appear to indicate that the reactivity of the benzoylperoxy radical with regard to double bonds is very high. In the case of a-methylstyrene, which by itself in the presence of oxygen forms a polyperoxide [58], [k3 (30°C) = 7 lmole-1 s-1 (polyperoxidation [59])] mainly epoxide and acetophenone are produced. 

Zinc and cobalt appear to occupy the same protein sites in alkaline phosphatase, as demonstrated by the results of competition between the two metals for these sites (Table II). Varying molar proportions of zinc are added to the apoprotein prior to addition of a five-fold molar excess of cobalt. Excess metal is removed by gel filtration and the cobalt incorporated is then measured. When cobalt alone is added to the apoprotein, nearly 4 gram atoms of the metal are incorporated (fine 1, Table II). In the remaining experiments, the sum of zinc and cobalt bound is nearly 4 in all instances. Hence, the four protein sites can apparently bind zinc and cobalt interchangeably (9). 

In addition to the general functions in which several minerals may be involved, each essential mineral has at least one specific role. Those which are present in large amounts, like calcium and phosphorus, are likely to have multiple and diverse roles. However, trace elements that are present at barely detectable levels, such as chromium and cobalt, appear to have highly specific functions centered around the organic molecules to which they are bound. 

Gobalt is a brittle, hard metal, resembling iron and nickel in appearance. It has a metallic permeability of about two thirds that of iron. Gobalt tends to exist as a mixture of two allotropes over a wide temperature range. The transformation is sluggish and accounts in part for the wide variation in reported data on physical properties of cobalt. 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Iron, cobalt, and nickel catalyze this reaction. The rate depends on temperature and sodium concentration. At —33.5°C, 0.251 kg sodium is soluble in 1 kg ammonia. Concentrated solutions of sodium in ammonia separate into two Hquid phases when cooled below the consolute temperature of —41.6°C. The compositions of the phases depend on the temperature. At the peak of the conjugate solutions curve, the composition is 4.15 atom % sodium. The density decreases with increasing concentration of sodium. Thus, in the two-phase region the dilute bottom phase, low in sodium concentration, has a deep-blue color the light top phase, high in sodium concentration, has a metallic bronze appearance (9—13). 

Reduction of sulfur dioxide by methane is the basis of an Allied process for converting by-product sulfur dioxide to sulfur (232). The reaction is carried out in the gas phase over a catalyst. Reduction of sulfur dioxide to sulfur by carbon in the form of coal has been developed as the Resox process (233). The reduction, which is conducted at 550—800°C, appears to be promoted by the simultaneous reaction of the coal with steam. The reduction of sulfur dioxide by carbon monoxide tends to give carbonyl sulfide [463-58-1] rather than sulfur over cobalt molybdate, but special catalysts, eg, lanthanum titanate, have the abiUty to direct the reaction toward producing sulfur (234). 

Cobalt is one of twenty-seven known elements essential to humans (28) (see Mineral NUTRIENTS). It is an integral part of the cyanocobalamin [68-19-9] molecule, ie, vitamin B 2> only documented biochemically active cobalt component in humans (29,30) (see Vitamins, VITAMIN Vitamin B 2 is not synthesized by animals or higher plants, rather the primary source is bacterial flora in the digestive system of sheep and cattle (8). Except for humans, nonmminants do not appear to requite cobalt. Humans have between 2 and 5 mg of vitamin B22, and deficiency results in the development of pernicious anemia. The wasting disease in sheep and cattle is known as bush sickness in New Zealand, salt sickness in Florida, pine sickness in Scotland, and coast disease in AustraUa. These are essentially the same symptomatically, and are caused by cobalt deficiency. Symptoms include initial lack of appetite followed by scaliness of skin, lack of coordination, loss of flesh, pale mucous membranes, and retarded growth. The total laboratory synthesis of vitamin B 2 was completed in 65—70 steps over a period of eleven years (31). The complex stmcture was reported by Dorothy Crowfoot-Hodgkin in 1961 (32) for which she was awarded a Nobel prize in 1964. 

---