Characteristics of Gasless Combustion of Core-Shell Al@NiO Microparticles with Boosted Exothermic Performance

The microstructures and thermochemical behavior of the energetic composites composed of core-shell structured μAl@NiO microparticles were characterized. These core-shell microparticles were synthesized using a wet-chemistry-based one-pot process, where the assembly was proposed to be driven by the electrostatic force between negatively charged Al and positively charged Ni-NH₃ ions. Electron microscopic images demonstrated the formation of NiO nanoparticles adhering to the surface of microsized Al particles with different equivalence ratios. Thermal analysis revealed two consecutive exothermic peaks resulting from the initial thermite reaction between 890 and 960 °C and subsequently the intermetallic/alloy formation reactions between 1000 and 1040 °C. The latter was further confirmed by the endothermic peaks of Al-Ni alloy melting at higher temperatures. The formation of alloy was substantiated by the melting of AlNi₃, AlNi, and Al₃Ni. The onset temperature of the first exothermic peak decreased with increasing nominal equivalence ratio of the core-shell. Compared to the physically mixed (PM) composite, the core-shell structures decreased the activation energy of the thermite reaction by a mere 9.24 kJ/mol; however, it increased the combustibility by the manifold. The PM composite was not able to be ignited at all by a 5 W laser, while the core-shell counterpart ignited at 2.55 ms and was completely combusted within 6.50 ms accompanying a violent impulse.