Standard enthalpies of formation of some borides of Ce, Pr, Nd and Gd by high-temperature reaction calorimetry

Abstract

The standard enthalpies of formation of five lanthanide borides have been determined calorimetrically at 1473 ± 2 K. The following values of ΔH_f⁰ are reported: PrB₆, − 51.3 ± 5.7 kJ/g · atom (this value was determined by solute-solvent drop calorimetry); CeB₄, − 53.5 ± 1.5 kJ/g · atom; PrB₄, − 53.1 ± 1.6 kJ/g · atom; NdB₄, − 53.3 ± 1.5 kJ/g · atom; Gd₂B₅, − 43.1 ± 1.4 kJ/g · atom (these four values were all obtained by direct synthesis calorimetry from the elements). The results are compared with earlier experimental data and with values predicted from Miedema's semi-empirical model. Finally, a systematic comparison is presented between the considered boride data and values for compounds of the rare-earth metals with Al, Ga, In and Tl taken from the published literature.