Calorimetric Studies of the Mg-Pt System

This study presents the limiting partial enthalpy of a solution of Pt in liquid Sn and Al baths, as well as, for the first time, the standard enthalpies of the formation of intermetallic phases and alloys of the Mg-Pt system, obtained using solution calorimetry. The alloys were prepared via mechanical alloying and subsequently examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The limiting partial enthalpy of a solution of Pt in liquid baths was measured at 931 K and 1033 K in the Sn bath and at 1036 K in the Al bath. The measured values are negative and equal to -126.0 ± 3.4 kJ/mol and -126.3 ± 3.5 kJ/mol at 931 K and 1033 K, respectively, in the Sn bath and -217.9 ± 1.2 kJ/mol in the Al bath. Subsequently, the measured heat effects were used to calculate the standard enthalpies of the formation of the intermetallic phases. The resulting values are as follows: -29.5 ± 1.8 kJ/mol·at. for Mg₆Pt, -53.9 ± 1.6 kJ/mol·at. for Mg₃Pt, -65.2 ± 0.4 kJ/mol·at. for Mg₂Pt, -78.7 ± 2.1 kJ/mol·at. for MgPt, -44.5 ± 0.4 kJ/mol·at. for MgPt₃, and -26.4 ± 1.0 kJ/mol·at. for MgPt₇. These values of the standard enthalpies of the formation of the intermetallic phases were compared with available ab initio data and those calculated using Miedema's model. The data obtained using Miedema's model were the least exothermic compared to the data obtained from calorimetric measurements and other theoretical calculations.