Theoretical assessment on mixing properties of liquid Tl–Na alloys

Abstract

Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calculations of surface tension reveal that results obtained from layered structure approach and compound formation model are in good agreement in the Na-rich side and in reasonable agreement in Tl-rich side of the composition, while those computed from Butler equation show noticeable deviations in the intermediate compositions. Both the viscosity and surface tension of liquid Tl–Na alloys increase with addition of Tl-component, viscosity having approximately linear variation with concentration. The study shows that there is non-linear variation in surface composition with bulk concentration and for most of the compositions the surface of the alloy is enriched with Na-atoms which segregate to the surface.

Keywords:

• Quasi-chemical model
• interaction energy
• viscosity
• surface tension

Acknowledgements

We (D. Adhikari and R.P. Koirala) are grateful to Dr George Kaptay, Professor, Department of Nanotechnology, University of Miskolc Egyetemvaros, Miskolc 3515, Hungary for providing necessary literature and inspiring discussion. One of the authors (R.P. Koirala) is grateful to Prof L.N. Jha (Former Head, Central Department of Physics, T.U., Kathmandu) and Prof Pradeep Raj Pradhan (Post-Graduate Department of Physics, M.M.A.M. Campus, T.U., Biratnagar) for fruitful suggestions and inspiring discussions.