Thermodynamics of the Al3Ni phase and revision of the Al-Ni system

The heat capacity of the Al3Ni phase had been measured for the first time, by means of relaxation method over the low temperature range 2-323 K and by measuring heat content increments using drop calorimetry over the higher temperature range of 583-1073 K. The Debye function was employed to fit the low-temperature heat capacities, and from the function, the absolute entropy was evaluated, S degrees(298) = 25.4 J/mol-atoms K. A three-term polynomial representation, a + b.T + c.T-2, was used for describing heat capacity above 298.15 K. The Gibbs energy function of the Al3Ni phase was derived with a fixed reference state by incorporating the polynomial expression of the heat capacity, the recently reported enthalpy of formation and the related phase equilibria in the Al-Ni system. A revised thermodynamic description of the entire Al-Ni system together with the calculated phase diagram is also presented. (C) 2010 Elsevier B.V. All rights reserved.