Thermodynamics Research Center / ThermoML | Thermochimica Acta

ABSTRACT

The heat of dissolution at infinite dilution of solid Nb in liquid Al was determined indirectly by dissolving small pieces of solid NbAl3 in liquid aluminum in an isothermal calorimeter at 1126 +- 0.5 K. A value of (infinity)Qdiss(NbAl3,298 K,1126 K) = 75.3 +- 3.0 kJ mol-1 was measured. The derived partial enthalpy of mixing at infinite dilution for Nb in Al is deltamixH(infinity) = -243.2 kJ mol-1. A lower limit for the solubility of solid Nb in liquid Al is also obtained from these measurements. The observed limit is 10 times higher than the accepted experimental value in the literature. In addition, heat content measurements for NbAl3 were performed at three different temperatures using drop calorimetry with empty crucibles. The measured heat contents are compared to values obtained from phonon calculations in the quasi-harmonic approximation. The quality of the determined heat of dissolution was checked by measuring the enthalpy of formation of solid NbFe2 and NbNi3. Values of -17.5 +- 2.9 kJ (mol of atoms)-1 and -30.7 +- 3.5 kJ (mol of atoms)-1 were found. These values agree with available experimental and theoretical data from the literature which confirms the validity of our experimental approach. A new, unknown and metastable magnetic configuration was discovered for NbFe2 in ab-initio simulations and will be discussed.