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, Á f G o T , of Mg 3 La 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 Á f G o T (Mg 3 La) 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 Á f G o T increases gradually, and it can be evaluated as a linear function of temperature above 350 K as follows:This result is expected to be useful as basic thermodynamic data of Mg-based alloys.

Thermodynamic and mechanical properties of lanthanum–magnesium phases from density functional theory

“…8a-c show the predicted C p (T ) for the cubic La-Mg compounds. The PBEsol results are in closer accord with experimental data from the literature for LaMg [51] and LaMg 3 [56]. However, all three figures suggest only very minimal differences between the PBE and the PBEsol.…”

“…It has been shown to absorb hydrogen to 4 wt.% at 300 • C [6]. Buschow found that LaMg 3 is a Pauli paramagnet [55] and Yamamoto et al [56] observed that the LaMg 3 valence band consists primarily of free electron gas-like Mg electrons with strongly localized 4f electrons from La. LaMg 3 has a narrow composition range at high temperatures [57].…”

Formation energies of the intermetallic compounds at the ground and thermally excited states determined by the ab initio energetic calculation and calorimetric measurement

“…(3), Δ f E total, T can be determined. Because the Δ f H values for the compounds have been determined by the acid solution calorimetry in our previous studies 11–15 as shown in Table I, these values were inserted into Eq. (3) in the present study.…”

“…(3) in the present study. The Δ f H values include inevitably experimental error of ±3 kJ mol −1 , described in our previous studies 11–15.…”

“…In our previous studies 11–15, the standard enthalpies of formation at 298 K, Δ f H , of the intermediate compounds of the Mg‐Zn and Mg‐La binary systems, Mg 0.48 Zn 0.52 11, Mg 0.4 Zn 0.6 12, Mg 0.333 Zn 0.667 13, Mg 0.154 Zn 0.846 13, Mg 0.75 La 0.25 14, and Mg 0.5 La 0.5 15 were determined by using a new Calvet‐type calorimeter equipped with a new thermoelectric device 16. Also, their isobaric heat capacity, C p , values were measured at 2–400 K by the recently developed method of relaxation calorimetry 17, 18 and at 400–650 K by the heat flow specially stabilized DSC 19–21.…”