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 as a major intermediate. The appropriate kinetic model for the reaction was evaluated by means of Malek's method (model selection technique). estak 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.