Heat of formation of FeNi70, FeNi73.5 and FeNi80 ordered alloys from the homogenous region of the FeNi3 phase

Solution calorimetry operated with a liquid Al bath has been used for the determination of enthalpies of formation of 3 ordered alloys containing 70, 73.5 and 80 at.% Ni from the FeNi3 homogenous phase region. The measured enthalpy of solution of nickel in aluminum at 1273 K is equal to 150 kJ g-atom-1. The temperature dependence of enthalpy of solution of Fe in Al was observed and the parabolic equation describing its dependence on temperature was worked out using also data available in the literature for temperatures between 971 and 1873 K. The investigations of the formation enthalpy were conducted at two temperatures and the average values were obtained to be -7.3 ± 1.5 kJ mole of atoms for FeNi70, -6.9 ± 1.2 kJ mole of atoms for FeNi73.5 and -6.8 ± 1.9 kJ mole of atoms for FeNi80. The values of the enthalpy of formation obtained in this work were more endothermic by 2.5 kJ mole of atoms and about 2.8 kJ mole of atoms in comparison with those calculated by the cluster variation and ab initio calculation method, respectively.