Bulk and surface properties of Co–Fe and Fe–Pd liquid alloys

• Co–Fe and Fe–Pd alloys in liquid state are segregating in nature.
• Ordering energy for both of these is temperature dependent.
• The atoms of the metals with lower surface tension tend to segregate in the surface.

We have employed quasi-chemical approximation to study the concentration dependence of bulk thermodynamic properties of two liquid alloys, Co–Fe and Fe–Pd at temperatures of 1863 K and 1873 K, respectively, at fixed atmospheric pressure. In order to investigate the surface structure in the alloys we have also performed a comparative study of surface tension using two statistical models. The study of the alloys indicates a positive deviation from the Raoultian behaviour with a higher degree of segregation in Fe–Pd system than that in the Co–Fe system. The surface tension is found to increase, both in Co–Fe and Fe–Pd alloys, with the addition of Fe-component. Furthermore, the surface segregation of the atoms of the metal with lower surface tension (Pd atoms in Fe–Pd alloy and Co atoms in Co–Fe alloy) is pronounced. Maximum surface segregation is expected to occur in the Co–Fe and Fe–Pd alloys around the compositions xCo = 0.5 and xFe = 0.8, respectively.