Alloys regular solution parameters

Table G. 1 reproduces values calculated by Miedema s model (Niessen et al. 1983) for the partial enthalpy of solution at infinite dilution of a liquid metal solute i in a liquid metal solvent i, AH, (in kJ/mole). For a i-j alloy, the regular solution parameter k can be approximated by [AHj(j( + AHJ(l)]/2.

In this equation, Qm is the molar surface area, m i is a structural parameter defined in Section 1.1 (see Figure 1.3) and A is the regular solution parameter of Ni-Si alloy defined by equation (4.3). From the slope of the osL(XNi) curve for XNi— 0, the adsorption energy is found to be E i,(f ) = —8.2 kJ/mole. Thus, in equations (1.2), all the quantities are known (or can be easily estimated), except W and Wf 1 which represent respectively the work of adhesion and the work of immersion of pure liquid Ni in metastable equilibrium with SiC (i.e., for a supposed non-reactive pure Ni/SiC system). The values deduced from equation (1.2) are Wj4 = 3.17 J/m2 and W = —1.35 J/m2 for pure Ni. They are reported in Figure 7.6 along with the corresponding value of contact angle. 

The VfT model has generally been used as the molecular model to study the solution thermodynamics of ternary and quaternary alloys in compound saniconductor alloys. Energy minimization techniques have been used to determine the interaction parameter in the regular solution theory and then, the binodal and spinodal curves have been calculated. Kim et al., have... 

A primary goal is to Investigate the combined Influences of conformational asymmetry (characterized by -y = Tb/Ta) and interaction or chemical asymmetry (characterized by A) on blend miscibility as conveniently quantified by the effective chi parameter of Eq. (5.6). Investigating the validity of regular solution, or Hildebrand, approaches is also of interest since it has been recently suggested to work surprisingly well for hydrocarbon polymer alloys based on experimental studies of polyolefin blends. For simplicity, we focus here on equimolar mixtures (< >= ), although the blend composition-dependence of the effective chi parameter is found to be very weak under the conditions of the calculations stated above." ... 

Here, Wg and Wq2 represent temperature and composition independent constants called Margules parameters. The substitution of Eq. (11) into Eq. (7) yields the equilibrium potential of the less noble component in the alloy. If this expression is subtracted from the equilibrium potential of the elemental phase defined by Eq. (1), the relation between the underpotentially co-deposited alloy composition and corresponding value of underpotential can be obtained. The example of this approach is shown in Fig. 6 where the composition of UPCD CoPt and FePt is measured as a function of deposition underpotential. The solid lines in the plot indicate the fit of the asymmetric regular solution model. It is important to note that Eq. (11) combined with Eqs. (7) and (1) suggest that composition of UPCD AB alloys (CoPt and FePt) is not dependent on A and B (Co and Fe) deposition kinetics (concentrations in the solutions). 

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