Thermodynamic characterization of NiAl

Thermodynamic properties of the high-stability intermetallic compound nickel aluminide, NiAl have been determined from mass-spectrometric, weight-loss effusion, and calorimetric measurements, using samples from a single preparation with a composition determined to be Ni0.986Al1.014. Per mole of NiAl molecules, the specific heat capacity at room temperature of 298 K is 48.54 J . K-1. mol(-1), with a linear temperature dependence of +0.0104 J . K-2 mol(-1). At the same temperature, the enthalpy of formation is - 133.7 kJ . mol(-1), the entropy is about 53.8 J . K-1 mol(-1) and the enthalpy difference between room temperature and absolute zero is 7.97 kJ . mol(-1). The Gibbs free-energy is - 130.2 kJ mol(-1) at T = 298 K, with a linear temperature dependence, of 6.04 J . K-1 . mol(-1). The Debye temperature is 452 K, while the electronic density-of-states at the Fermi-level is about 0.29 states per eV-atom. The NiAl* tons were observed in the high-temperature mass spectra. Pressures for the gas at these temperatures were estimated and used with the results of quantum-mechanical calculations of total energy, specific heat, and entropy to calculate free-energy functions for the gas. These and additional results are compared with other measurements and discussed in terms of current theories of the electronic and structural properties of the compound. (C) 2009 Elsevier Ltd. All rights reserved.