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A high-speed electrothermography approach is applied to investigate the mechanism and kinetics for nanostructured Al/Ni foils. Application of the Kolmogorov−Johnson−Mehl−Avrami and adiabatic thermal explosion models reveal that the activation energy for nucleation appears to be much higher than that for the reaction. It is shown that formation of intermetallic nuclei is the limiting step that defines the ignition characteristics of the foils at temperatures below 500 K, while the process is reaction-limited at higher temperatures. Nucleation is also shown to play an important role during rapid (∼10 m/s) propagation of the combustion (reaction) wave along the Al/Ni foils. These findings suggest new approaches for controlling the ignition and combustion processes for nanostructured reactive materials.

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Functional features of Ni-W composite materials combined with successful performance enabled a breakthrough in their broad application. To disclose the formation pathway of Ni-W composite materials at extreme conditions of combustion synthesis in the NiO-WO3-Mg-C and NiWO4-Mg-C systems for the optimization of the synthesis procedure, the process was modeled under programmed linear heating conditions by thermal analysis methods. The reduction kinetics of tungsten and nickel oxides mixture and nickel tungstate by Mg + C combined reducer at non-isothermal conditions was studied at high heating rates (100–1200 °C min−1) by high-speed temperature scanner techniques. It was shown that when moving from low heating to high heating rates, the mechanism of both the magnesiothermic and magnesio-carbothermic reductions of the initial mixtures changes; that is, the transition from a solid-solid scheme to a solid-liquid scheme is observed. The strong influence of the heating rate on the reduction degree and kinetic parameters of the systems under study was affirmed. The simultaneous utilization of magnesium and carbon as reducers allowed the lowering of the starting and maximum temperatures of reduction processes, as evidenced by the synergetic effect at the utilization of a combined reducer. The effective values of activation energy (Ea) for the reactions proceeding in the mixtures NiO + WO3 + 4Mg, NiO + WO3 + 2.5Mg + 1.5C, NiWO4 + 4Mg and NiWO4 + 2Mg + 2C were estimated by Kissinger isoconversional method and were 146 ± 10, 141 ± 10, 216 ± 15 and 148 ± 15 kJ mol−1, respectively.

Kinetic studies were performed utilizing high-speed temperature scanner in the Ni-Al system including those with and without mechanical activation (MA) of different duration in a planetary ball mill, with and without using carbon nanoadditives (NA). The temperature profiles were taken and treated at different heating rates from 100 up to 2600 °C/min considering the influence of activation duration and the role of nanoadditive on the characteristic points of thermograms. Kissinger method allowed to evaluate activation energy (Ea) for non-activated, activated (1, 2, 3, 5 min), nanoadditive (1 wt.%) containing and nanoadditive (1 wt.%) containing mechanoactivated (1, 3, 5 min) mixtures. The beneficial influence of NA on the interaction between Ni and Al in the non-activated and moderately mechanoactivated mixtures was demonstrated. The influence of MA and NA on the microstructure features and phase formation sequence at various heating rates were revealed. For all the mixtures under study, T* characteristic temperatures (the temperature, where the maximum exothermic effect was observed) were found to increase with increasing heating rates. It was unravelled that mechanical treatment leads to significant changes in the reaction kinetics and phase formation laws. Particularly, in an activated mixture, the formation of Ni3Al is followed by NiAl intermetallic, in contrast to non-activated mixture, where the reaction proceeds only with the NiAl formation. The both MA in 1 min and addition of 1 wt.% NA decreased the activation energy of the Ni-Al reaction, exhibiting commensurate impact on the effective activation energy value of the Ni-Al system. However, > 3 min MA in the presence of 1 wt.% NA have prohibitive effect on the reaction in the Ni-Al system.