Nickel-Coated Aluminum Nanoparticles for Modulating Ignition Temperature: Interfacial Chemistry and Mechanism
Yuxin Zhou, Lei Yang, Ashvin Kumar Vasudevan, Matthew Dickson, Mahbub Chowdhury, Keren Shi, Michael R. Zachariah
Abstract
Metal particles such as Al always have a native oxide shell, which acts as a barrier to unintended ignition but can also significantly retard the combustion chemistry. Herein, we present a strategy to trigger ignition using Al–Ni intermetallic reactions. The approach involves synthesizing Ni-coated Al (Al@Ni) nanoparticles, whose ignition temperature can be significantly reduced (up to ∼230 K), and the reduction can be tuned by adjusting the amount of Ni deposited via a kinetic control strategy. The underlying ignition enhancement mechanism of Al@Ni is explored through differential scanning calorimetry, environmental transmission electron microscopy, and reactive molecular dynamics simulations. Two major factors contribute to the reduced ignition temperature: (1) the highly exothermic Al–Ni intermetallic reaction that occurs before ignition, driven by the diffusion or bulk flow of Al from the Al core through the oxide shell to Ni, and (2) the retardation of Al nanoparticle sintering, which is beneficial to both ignition and consequent oxidation reactions. Owing to the decreased ignition temperature, Al@Ni-based propellant demonstrates an ∼26% higher regression rate compared to native Al.