Cobalt-iron equilibrium

Cobalt-iron alloys were deposited from a sulfate electrolyte containing a sum of 1 mol dm metal salt. 0.5 mol dm H3BO4 were added and subsequently the pH was adjusted to pH = 2.0. No additives were used. The deposition was carried out at three different potentials and under potentiostatic control on copper substrates. The results at 1.0 V deposition potential are presented in Figure 8.6. The dependence is approximately described by curve 1 in Figure 8.5. The system can be described as an equilibrium system. The deviation below 30% of iron ions in the electrolyte may be connected with differences in the crystallographic structure. In this region a mixture of fee and bcc structure was... 

Gia] Gianoglio, C., Quadrini, E., Equilibrium Distribution of the Solid Solutions of the Cobalt-Iron-Boron System (in Italian), Atti Acad. Sci. Torino I. Classe Set. Fis., Mathem. Natur., 114(3-4), 319-327 (1980) (Experimental, Phase Diagram, 9)... 

It is interesting to note, as pointed out to me by Mr. J. L. Hoard, that these considerations lead to an explanation of the stability of trivalent cobalt in electron-pair bond complexes as compared to ionic compounds. The formation of complexes does not change the equilibrium between bivalent and trivalent iron very much, as is seen from the electrode potentials, while a great change is produced in the equilibrium between bivalent and trivalent cobalt. 

An example for a compound of the perovskite type is LaNiOj. In other com-ponnds of the perovskite type, nickel may be replaced by cobalt or iron, and lan-thannm in part by alkaline-earth metals, an example being Lag 8Sro2Co03. The activity of perovskites toward cathodic oxygen reduction is low at room temperature but rises drastically with increasing temperature (particularly so above 150°C). In certain cases the activity rises so much that the equilibrium potential of the oxygen electrode is established. 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

A number of metals, such as copper, cobalt and iron, form a number of oxide layers during oxidation in air. Providing that interfacial thermodynamic equilibrium exists at the boundaries between the various oxide layers, the relative thicknesses of the oxides will depend on the relative diffusion coefficients of the mobile species as well as the oxygen potential gradients across each oxide layer. The flux of ions and electrons is given by Einstein s mobility equation for each diffusing species in each layer... 

Estimates of the Mars core composition by the authors listed above suggest it is made of metal plus iron sulfide, the latter varying from 29 to 44 wt.%. Abundances of siderophile (tungsten, phosphorus, cobalt, molybdenum, nickel) and chalcophile (indium, copper) elements in the mantle (Fig. 13.23) are consistent with equilibrium between sulfide, metal, and mantle silicate at high temperature and pressure (Righter and Drake, 1996). 

The Raman laser temperature-jump technique has been used in studies of a variety of spin-equilibrium processes. It was used in the first experiment to measure the relaxation time of an octahedral spin-equilibrium complex in solution (14). Its applications include investigations of cobalt(II), iron(II), iron(III), and nickel(II) equilibria. 

An experimental study of kinetics of ammonia synthesis on iron (101), cobalt, and nickel (96) catalysts, at ammonia concentrations much lower than that at equilibrium, showed that at pressures of the order of 1 atm the second of these possibilities is realized.7 When far from equilibrium, the... 

The spin state lifetimes in solution of the complexes II and III have been measured directly with the laser Raman temperature-jump technique189). Changes in the absorbance at 560 nm (CT band maximum) following the T-jump perturbation indicate that the relaxation back to equilibrium occurs by a first-order process. The spin-state lifetimes are r(LS) = 2.5 10 6 s and r(HS) =1.3 10 7 s. The enthalpy change is AH < 5 kcal mol-1, in good agreement with that derived from x(T) data in Ref. 188. The dynamics of intersystem crossing processes in solution for these hexadentate complexes and other six-coordinate ds, d6, and d7 spin-equilibrium complexes of iron(III), iron(II), and cobalt(II) has been discussed by Sutin and Wilson et al.u°). 

The addition of cobalt to a nickel ferrite has been employed to increase resistivity, as illustrated in Fig. 9.24. For an explanation it is necessary to consider the third ionization potentials of chromium, iron, manganese, cobalt and nickel, which increase in this order. The addition of cobalt tends to maintain the iron in the Fe3+ state by virtue of the equilibrium... 

Reduction of Metallic Oxides.—Hydrogen can displace many metals from their oxides, the reduction taking place at the ordinary temperature, as with silver and palladium oxides, or on heating, as with the oxides of copper, cadmium, lead, antimony, nickel, cobalt, and iron. Sometimes these reductions are incomplete, an equilibrium being attained. Such equilibria depend on the experimental conditions, an example being the action of steam on heated iron (p. 15). 

The polarographic determination of manganese, iron, cobalt and nickel is not so often used as that of the above mentioned elements. Probably, competition with other analytical methods is the main reason. However, the polarography of these metals has been thoroughly investigated and it is frequently used for studies of equilibrium constants of their complexes. 

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