The cobalt-iron alloy system

In the case of the CoFe alloy system, the elementary kink site transformations for alloy crystallization can be represented by the following four equilibrium reactions 

The surface density of the principal four kink site positions (in square brackets) is related to the ion concentration of the two components Co and Fe in the electrolyte, described by and Cp, by the equations 

The exponential term describes the potential dependence of the equilibrium. 

PcoFe = [CoFe ] / ([CoCo ] + [CoFe ]) = 1 - PcoCo FFeCo = [FeCo ] / ([FeCo ] + [FeFe ]) 

The probability can be expressed by the equilibrium constants and ion concentrations in the electrolyte bath by insertion of the relations (8.32) for the active atoms in the kink site positions in Eq. (8.33a-d). The relation between the alloy composition and electrolyte concentration is derived by the procedure described in Section 8.6.1. 

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A system very similar to the cobalt-iron alloy system is CoNi. CoNi 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 under potentiostatic control on copper substrates. The deposition was independent on the potential between 0.8 and 1.6 The results are presented in Figure 8.9. 

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