Thermodynamic, surface and transport properties of liquid Hg–Pb and Hg–In amalgams Nalini Sharma a, ⁎, Anil Thakur b , P.K. Ahluwalia a a Physics Department, Himachal Pradesh University, Shimla 171005, India b Physics Department, Government College Solan, Himachal Pradesh 173212, India abstract article info Article history: Received 11 April 2013 Received in revised form 2 October 2013 Accepted 4 October 2013 Available online 16 October 2013 Keywords: Binary liquid alloys Thermodynamic Short range order Diffusion Surface tension 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 (G M ), heat of mixing (H M ), entropy of mixing (S M ), microscopic functions (concentration fluctuations S cc (o) and the Warren Cowley short range order parameter (α 1 )) 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 (D M /D id ) which shows that the maximum deviation from ideal values (D M /D id = 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 H g Pb 2 and HgIn complexes in liquid Hg–Pb and Hg–In alloys, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Formation of compounds in solid state, led many [1,2] to believe in the existence of chemical complexes and pseudo molecules (i.e. group of atoms) near melting temperature in binary molten alloys. It is known that most binary alloys are far from ideal solutions and reveal an inhomogeneous atomic distribution. Faber [3] was the first to study the compound formation in the liquid metals and their alloys. Later Bhatia and coworkers developed a theory called conformal solution model [1,2] and applied it to binary liquids and alloys. The mixing behaviour of such alloys is generally understood [4] through con- centration dependent thermodynamic properties and microscopic functions such as free energy of mixing G M , heat of mixing H M , entropy of mixing S M , concentration fluctuations at long wavelength limit S cc (o), short range order α 1 . In the study of thermodynamic properties of liquid alloys [5] interaction approximation [2] has provided a well established framework. Lately [6–9] there has been a lot of interest in liquid alloys showing tendencies for simultaneous formation of two compounds. The thermodynamic properties of compound forming binary liquid alloys can show anomalous behaviour that can be deduced from the asymmetry of their concentration dependent property curves. The alloys of alkali metals e.g. Na–Pb and Li–Pb show volume expansions or contractions at specific concentration. These expansion and shrinkage are usually understood at the cost of charge transfer among the constituent species. These alloys display complex phase diagrams [10] and a very peculiar variation of the chemical bonding. Formation of the compound takes place at a particular temperature. The phase separation takes place as the temperature increases or decreases. Therefore, the thermodynamic properties of binary liquid alloys have been studied at compound forming temperature only as indicated by the respective phase diagrams [10–13]. Since the work by Bhatia and Thornton [1], the concentration–concentration fluctuations in long wavelength limit S cc (o) have proved very useful in obtaining microscopic information about molten alloys. The knowledge of S cc (o) with short range order α 1 parameter for nearest neighbour shell shed light on phenomena of easy glass formation in many binary molten alloys. Various models like Young’s conformal model 1992 [14], Bhatia and Singh's quasi-chemical model 1984 [15], Singh and Sommer’s thermodynamic model 1992 [16], Hoshino’s compound formation model 1983 [17] and Prasad et.al.’s compound formation model 2007 [18] have been used to study and understand the alloying behaviour of compound forming liquid metal alloys. All the theoretical models explain that interatomic interactions play an important role in compound formation. Many metallurgical processes required the knowledge of diffusivity of liquid metals. Knowledge of diffusion coefficients of metals in mercury is important in the study of electrode Journal of Molecular Liquids 188 (2013) 104–112 ⁎ Corresponding author. Tel.: +91 9418114597. E-mail address: nalini_2808@yahoo.co.in (N. Sharma). 0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2013.10.004 Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq