Cobalt atomic properties

Another chemically more interesting spin labeled B12 derivative involves coordinate attachment of the nitroxyl function to the cobalt atom of a cobinamide. Fig. 22 shows a reaction in which an alkyl cobin-amide is mixed with 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl. The nitroxide displaces water from the 6th coordination position very slowly and therefore this reaction is usually allowed to proceed for a few days with a large excess of nitroxide. From the properties of the coordinated nitroxide derivative discussed below, it is certain that the cobalt is coordinated by the N—O functional group. An analogous compound to that shown in Fig. 22 can be made with a similar nitroxide in which the 4-hydroxyl-group is missing. In this case the N—O-function is the only basic site on the molecule and therefore must be the position of attachment to the cobalt 119). 

Occurrence of Cobalt—History—Preparation—Pyrophoric Cobalt—Physioal Properties—Ooelusion of Hydrogen—Chomioal Properties—Atomic-Weight —Uses -Electro-deposition—Alloys. 

An essential property of coenzyme B12 is the weakness of its cobalt-carbon bond, which is readily cleaved to generate a radical. To facilitate the cleavage of this bond, enzymes such as methylmalonyl CoA mutase displace the benzimidazole group from the cobalamin and bind to the cobalt atom... 

Physical and Chemical Properties Cobalt (atomic number 27, atomic mass 58.9332, CAS Registry Number 7440-48-4) belongs to Group VIIIB of the transition ele-... 

The thennal properties of cobalt in THFA are shown in Fig. 6. The pyrolysis temperature can be set to 1600°C. However, the continuous increase of the atomization curve indicates that cobalt atomization is not quantitative even at the maximum temperature allowable to the THFA tube (2500°C). 

Williams and co-workers have given a preliminary account of kinetic studies on the substitution of co-ordinated carbanions in Co corrinoids. This group of compounds, which contain the corrin ring of Bjg, can be prepared with a wide range of carbanions in one of the axial positions of the cobalt atom. In previous papers the authors had studied the effect of the co-ordinated carbanion on the properties of the other ligands in the complex (i.e. its cis and trans effects) and in this work they wished to establish whether reactions which involve the carbanions themselves... 

In the reaction between trichlorocobaltate and chloride ions, the role of the donor properties of the solvent is more marked, probably because the fourth coordination site of the cobalt atom in the trichloro complex is occupied by a solvent molecule. The higher the donor strength of the solvent, the more difficult it is to replace it with chloride ion. On the other hand, the magnitude of the coefficient of AN shows that the acceptor strength of the solvent also exerts an influence on the system. This is manifested predominantly via solvation of the chloride ion, since coordination of the chloride to the cobalt also assumes desolvation of the chloride ion. 

The main problem in explaining the physicochemical nature of cobalt monosilicide is to find a correlation between the crystal-chemical scheme proposed above and the band representations describing the electrical properties. The comparatively small values of the effective masses of the carriers in CoSi suggests that the overlapping bands responsible for its thermoelectric properties are fairly wide (about 1 eV). From this, it must be assumed that 4p and 4pj, levels of cobalt atoms form molecular bonding orbitals with six adjacent metal atoms which, when the degeneracy is removed in the crystal, form two bands overlapping by 0.05 eV. 

It also e lains the magnetic properties of cobalt mono-silicide the absence of unpaired electrons determines the low magnetic susceptibility, and the slight increase of susceptibility with temperature is e lained by an increase in the density of carriers (holes and electrons) as the band overlap increases at a rate of about 4 10" eV/deg C. Finally, the scheme is consistent with the donor nature of nickel atoms and the acceptor nature of iron, which have been established ejq)erimentally, when these partially replace the cobalt atoms in cobalt mono-silicide. 

Iron atoms in its monosilicide have one 3d electron less than cobalt atoms (Fig. 3). In the energy scheme (Fig. 4a) this is reflected by the disappearance of electrons from the 4p bonding state band, which should lead to a semiconductor type of conductivity (Fig. ). From the experimental data on the thermoelectric and magnetic properties of FeSi which have been quoted, it follows that the scheme shown in Fig. 4b is, apparently, applicable at low temperatures. 

As a very important topic in contamination buildup, the question is still open to what extent the data on corrosion product solubilities in the primary coolant are of importance for the behavior of trace amounts of cobalt. It seems to be still questionable whether cobalt ferrites as a well-defined compound with properties similar to the nickel ferrites can exist under PWR primary coolant conditions, whether cobalt atoms can be incorporated into a nickel ferrite lattice or whether traces of cobalt may be deposited onto the surfaces of the reactor core by adsorption on other, already deposited oxides. Such adsorption processes may occur even on the Zircaloy oxide films in the absence of any net deposition of corrosion products. Experimental investigations of the interaction of dissolved cobalt with heated Zircaloy surfaces (Lister et al., 1983) indicated that at low crud levels in the coolant cobalt deposition on surfaces is dominated by processes involving dissolved species, with adsorption/desorption processes being the responsible mechanisms. The extent of cobalt deposition is controlled by the type of oxide present on the Zircaloy surface thin black films of zirconium oxide will pick up less cobalt from the solution than thick white oxide films, even when the differences in the available surface areas of both types of oxides are taken into account. The deposition process seems to be little affected by the heat flux in the exposed metal. According to Thornton (1992), such adsorption-desorption exchange processes provide a pathway for radioactive species to be transported around the circuit even when the net movement of corrosion products is minimized this means that under such circumstances the processes of activity transport and of corrosion product transport may be decoupled. They may provide a pathway for target nuclides such as Co to be adsorbed onto fuel rod surfaces even in a core which is virtually free of deposited corrosion product particles. 

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