Calorimetric Studies of Magnesium-Rich Mg-Pd Alloys

Solution calorimetry with liquid aluminum as the bath was conducted to measure the enthalpy of a solution of magnesium and palladium as well as the standard formation enthalpies of selected magnesium-palladium alloys. These alloys were synthesized from pure elements, which were melted in a resistance furnace that was placed in a glove box containing high-purity argon and a very low concentration of impurities, such as oxygen and water vapor. A Setaram MHTC 96 Line evo drop calorimeter was used to determine the energetic effects of the solution. The enthalpies of the Mg and Pd solutions in liquid aluminum were measured at 1033 K, and they equaled −8.6 ± 1.1 and −186.8 ± 1.1 kJ/mol, respectively. The values of the standard formation enthalpy of the investigated alloys with concentrations close to the Mg6Pd, ε, Mg5Pd2, and Mg2Pd intermetallic phases were determined as follows: −28.0 ± 1.2 kJ/mol of atoms, −32.6 ± 1.6 kJ/mol of atoms, −46.8 ± 1.4 kJ/mol of atoms, and −56.0 ± 1.6 kJ/mol of atoms, respectively. The latter data were compared with existing experimental and theoretical data from the literature along with data calculated using the Miedema model.

Drop calorimetry of the compounds NbCl5, TaCl5, RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6

Enthalpy contents for NbCl5, TaCl5, RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6 were measured as functions of temperature using a high temperature aluminum block drop calorimeter. It was found that the solid compounds RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6 undergo allotropie solid–solid transformations and the enthalpies and entropies associated with these phase changes, as well as from fusion, have been evaluated.Molar heat capacities for the systems investigated are reported as linear functions of temperature.The molar heat capacities for solid and molten NbCl5 or TaCl5 were used together with available vapour pressure data to express enthalpies and free energies of vaporization for these compounds as functions of temperature through the third law calculation method. Keywords: calorimetry, heat capacities, transition enthalpies, niobium compounds, tantalum compounds.