Intermetallic reaction and eutectic transitions tune the reactivity in core-shell Mg/Ni nanoparticles

There is developing interest in tuning interfaces to manipulate the performance and safety of energetic materials comprising metallic fuels. One approach is to employ a core-shell architecture to trigger pre-ignition reactions. Here, we investigated the dynamic interfacial reactions and diffusion pathways of synthesized nickel-coated magnesium nanoparticles with sub-nanometer spatial and millisecond temporal resolution under controlled heating by in situ TEM, complemented by ex situ reactivity characterization. Upon heating, outward diffusion of Mg into the Ni shell forms an intermediate Mg₂Ni phase, directly evidenced by TEM diffraction. This highly exothermic alloying rapidly elevated particle temperature, initiated eutectic melting at the Mg-Ni interface, and accelerated completion of outward Mg transport at temperatures well below those of uncoated Mg. By tuning the Ni-shell thickness, we reduced the ignition temperature by up to ∼200 °C. Overall, our study provides valuable insights into the development of designing energetic materials with safer operation and precisely controlled energy release.