Standard Gibbs energy of formation of MgLa determined by solution calorimetry and heat capacity measurement from near absolute zero kelvin

摘要

The standard Gibbs energy of formation, triangle open_fG deg_T, of MgLa in the temperature range from near absolute 0 to 525 KAPPA were determined by calorimetry. The heat capacities, C_p, from 2 K to 525 KAPPA were measured by the relaxation method and DSC. Also, a thermal anomaly at 5.9 KAPPA, which appeared to be a superconductive phase transition, was found in the obtained C_p values. The triangle open_fG deg_T (MgLa) 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 300 KAPPA, the triangle open_fG deg_T increases gradually, and it can be evaluated as a linear function of temperature above 300 K as follows:triangle open_fG deg_T(MgLa) (kJmol~(-1)) = -39.236 - 6.9832 x 10~(-3) T + 2.1016 x 10~(-3) T log T + 1.9114 x 10~(-5) T~2 - 0.81004 T~(-1) + - 7.40 (2 - 300KAPPA), triangle open_fG deg_T(MgLa) (kJmol~(-1)) = -41.100 +9.9974 x 10~(-3)T+ - 7.40 (300-525KAPPA). This result is expected to be useful as basic thermodynamic data of Mg-based alloys.