Thermo-kinetic analysis of Ni–Al intermetallic phase formation in powder system: A case of complex solid–solid reactions

Thermo-kinetic analysis was carried out to determine the kinetics of Ni–Al intermetallic phase formation from powder mixture of Ni and Al. The kinetic data were generated using dynamic temperature program at 5, 10, 15, 20 K min⁻¹ in a differential scanning calorimeter. The phase formation was studied with the help of both qualitative and quantitative powder X-ray diffraction using Rietveld refinement. The activation energy for the reaction was calculated from model-free isoconversional technique employing both differential (Friedman’s method) and integral (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose method) methods. The result shows that formation of NiAl from elemental powders is multi-step in nature involving Ni <inf>2</inf>Al <inf>3</inf> as a major intermediate. The appropriate kinetic model for the reaction was evaluated by means of Málek’s method (model selection technique). Šesták Breggren (auto-catalytic model) was found to be in good agreement with the experimental data. The corresponding kinetic parameters and rate expression were determined for the reaction system involving solid–solid reaction between Ni and Al in the powder form.