Enthalpy of formation of B13Li, B14Li3 and B3Li (B6Li2) compounds measured with reaction calorimetric method

The formation enthalpies of B13Li, B14Li3 and B3Li (B6Li2) compounds were measured using a reaction calorimetric method. The phases were prepared in a glove-box filled with high purity argon. The phases were annealed for two days and next studied with X-ray diffraction and electron microscopy methods. It was experimentally found that the dissolution of boron in liquid aluminum, used as solvent in many earlier experiments, was so slow in comparison with other metals that another method had to be selected. The experiments were conducted using a water calorimeter working at room temperature in air. Samples of Li and phases were delivered from the glove-box to the calorimeter in a closed glass little bottle and transferred quickly into water directly before the experiment. The enthalpy of lithium reaction with water was measured to be equal −205.3 ± 1.2 kJ/gram-atom. As the boron did not react with water, its reaction heat effect with water was assumed to be zero. The formation enthalpy value obtained for the B13Li, B14Li3 and B3Li (B6Li2) compounds were equal to −14.1 ± 0.1, −33.2 ± 1.6 and −43.6 ± 1.8 kJ/mol of atoms, respectively.

► Preparation and identification of B13Li, B14Li3, and B3Li phases by X-ray analysis. ► Water as solvent for Li, B13Li, B14Li3, and B3Li phases. ► X-ray analysis of residue after B13Li, B14Li3, and B3Li dissolution. ► Enthalpy of formation for B13Li, B14Li3, and B3Li phases.