Standard Gibbs Energy of Formation of Mg₃La Determined by Solution Calorimetry and Heat Capacity Measurement from Near Absolute Zero Kelvin

Abstract

The standard Gibbs energy of formation, Δ_fG^o_T, of Mg₃La in the temperature range from near absolute zero Kelvin to 525 K were determined by calorimetry. The heat capacities, C_p, from 2 K to 525 K were measured by the relaxation method and DSC. The Δ_fG^o_T(Mg₃La) values were determined by combining the C_p 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_fG^o_T increases gradually, and it can be evaluated as a linear function of temperature above 350 K as follows:
Δ_fG^o_T(Mg₃La)/kJ mol⁻¹
 =−76.204−2.5304×10⁻² T+1.2160×10⁻² T log T
   +1.1814×10⁻⁵ T²−0.80332 T⁻¹±17.0 (2–350 K)
Δ_fG^o_T(Mg₃La)/kJ mol⁻¹=−79.652+1.9567×10⁻² T±17.0 (350–525 K).
This result is expected to be useful as basic thermodynamic data of Mg-based alloys.