Standard Gibbs Energy of Formation of Mg<SUB>3</SUB>La Determined by Solution Calorimetry and Heat Capacity Measurement from Near Absolute Zero Kelvin

Abstract

The standard Gibbs energy of formation, Δ f G° Τ , of Mg 3 La in the temperature range from near absolute zero Kelvin to 525 K were determined by calorimetry. The heat capacities, Cp, from 2 K to 525 K were measured by the relaxation method and DSC. The A f G° T (Mg 3 La) values were determined by combining the Cp data with the standard enthalpy of formation at 298 K which was measured by the Calvet-type calorimeter using hydrochloric acid solution. From 2 to 350 K, the Δ f G° Τ increases gradually, and it can be evaluated as a linear function of temperature above 350 K as follows: Δ f G° Τ (Mg 3 La)/kJ mo -1 =-76.204-2.5304 x 10 -2 T+ 1.2160 x 10 -2 T log T + 1.1814 x 10 -5 T 2 - 0.80332 T -1 ± 17.0 (2-350K) Δ f G° T (Mg 3 La)/kJmol -1 =-79.652+1.9567 x 10 -2 T ± 17.0 (350-525K). This result is expected to be useful as basic thermodynamic data of Mg-based alloys.