Solutions of group IV elements in liquid lithium. Solubilities, enthalpies of solution and solvation enthalpies

Abstract

The solubilities of tin (0.00 ⩽x_Sn⩽ 0.0129) and of lead (0.00 ⩽x_Pb⩽ 0.0140) in liquid lithium have been determined by equilibrium resistivity methods and can be represented by the equations: ln x_Sn= 4.742 – 6794/T 579 ⩽T/K ⩽ 745, ln x_Pb= 5.717 – 6722/T 513 ⩽T/K ⩽ 670. The sensitivity of the solubilities of the Group IV elements to the overall phase relationships is noted, that for carbon being much smaller than those for the heavier elements, which vary according to the trend: Sn Si < Ge < Pb. The anomalously low solubility of tin is correlated with the correspondingly high melting point and exothermic enthalpy of formation of Li₂₂Sn₅. A simple thermochemical cycle is used to demonstrate that, whereas carbon dissolves endothermically in both liquid lithium and liquid sodium, the heavier Group IV elements dissolve exothermically. A similar cycle is used to derive solvation enthalpies (for the neutral gaseous species) for all Group IV elements in the two solvents. The trend in solvation enthalpy: C > Si > Ge > Sn > Pb is indicative of a diminishing affinity of solvent for solute and is attributed to the increasing metallic character of the solute as the Group is descended.