Thermodynamic, surface and transport properties of liquid Hg-Pb and Hg-In amalgams

The complex formation model is used with a view to study the effect of complex or compound formation on thermodynamic and surface properties of Hg-Pb and Hg-In liquid amalgams through the calculation of free energy of mixing (GM), heat of mixing (HM), entropy of mixing (SM), microscopic functions (concentration fluctuations Scc(o) and the Warren Cowley short range order parameter (α1)) for whole concentration range at compound forming temperatures of 600 K and 298.15 K, respectively. The mixing behaviour of these alloys has been examined by computing ratio of diffusion coefficients (DM/Did) which shows that the maximum deviation from ideal values (DM/Did = 1) occurs around compound forming concentration. Surface properties have also been analysed using two different approaches which reveal that with the addition of Pb in Hg-Pb alloy, surface tension of alloy decreases and Pb atoms tend to segregate at the surface, while surface tension of Hg-In alloy increases with the addition of In. Increase in surface tension value in between 0.5 and 0.8 atomic fractions of In supports compound formation in this range of concentration, which is also supported by the results of thermodynamic properties. The results also show that the ordering energies are temperature dependent and thermodynamic parameters are in reasonable agreement with the experimental results. The analysis of these properties suggests the presence of HgPb2 and HgIn complexes in liquid Hg-Pb and Hg-In alloys, respectively.