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ACTIVITY OF THE ALKALI METALS IN THEIR LEAD BASED BINARY LIQUID ALLOYS


P. K. Karn
Page No. 13-17


Abstract

Alkali metals are highly reactive. Within a binary alloy they generally form complexes. Due to
formation of such complexes the thermodynamic properties of the alloys often show asymmetry
around equi-atomic composition. In the present work we have considered two lead based binary
alloys of alkali metals e.g. Li-Pb and Na-Pb. The phase diagrams of these alloys reveal that at their
liquid state complexes are formed. We have confined our study in computing the activity of lithium
and sodium within these molten alloys. Activity is one of the fortunate thermodynamic functions
which can be measured directly by experiment. For the purpose of our theoretical study Flory’s
model has been employed. It is a statistical mechanical model based on the size factor of the
constituent species of a binary liquid alloy. For each alloy we have started with the mathematical
expression for the free energy of mixing according to this model and found out the interchange
energy between the ingredients from the observed values of the former by the method of successive
approximations. Using this value of the interchange energy finally the activity of the concerned
alkali metal has been computed for different concentrations. Our calculation indicates that the
lithium-lead liquid alloys are structurally disordered at lower concentrations of lithium.
Key words: Binary liquid alloys, Alkali metals, Lead based alloys, Flory's model, Free energy of
mixing, Interchange energy, Activity.


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