Study of nickel-coated aluminum nanoparticles using molecular dynamic simulations and thermodynamic modeling

Aluminum nanoparticles have widely been used as fuel additives to solid propellants for rocket propulsion, but the formation of the oxide layer has been a setback for their application. A viable solution to this problem is to passivate aluminum (Al) with a layer of nickel (Ni), which offers multiple advantages. The current study focuses on energetic intermetallic interaction within Ni-coated Al nanoparticles and also the interaction/coalescence between two Ni-coated Al nanoparticles of varying sizes. Molecular dynamics (MD) method is employed to study the size-dependent variation of these interactions. A thermodynamic formulation is devised to calculate the adiabatic reaction temperature of single as well as coated nanoparticles. The results obtained using this formulation are compared with the results obtained from MD simulations. The estimation of dead layer thickness formed at the interface of Ni and Al is critical to correctly capture the energetic behavior. In this work, the dead layer thickness is estimated and used to predict the adiabatic reaction temperature of the coalescence of two equal-/unequal-sized Ni-coated Al nanoparticles. It has been found that particle size can affect the adiabatic reaction temperature because of the varying surface energy. It has also been found that the dead layer thickness plays a vital role in accurately determining the adiabatic reaction temperature of the system. It has been observed that the reaction time decreases proportionately with increase in specific reaction surface area (between Al and Ni) for single as well as coated particles.