Molecular dynamics study of sintering of Al nanoparticles with/without organic coatings

Abstract

Sintering is one of the key factors limiting the application of aluminum nano particles (ANPs) as additives in solid propellant. Because of its high specific surface area and the surface is covered by atoms with low coordination number, ANPs are prone to aggregate or sinter even during the production process which blocks the energy release of ANP during combustion. We perform reactive molecular dynamics simulations to study sintering behaviors for bare and ethanol coated ANPs. Several parameters including shrinkage ratio, gyration radius and moment of inertia are responsible for judging the progress of particle sintering process. A three-stage sintering process has been observed. ANPs follow different sintering laws below and above their melting temperatures. At the same temperature, the smaller the ANP size, the faster the sintering process ends. Before melting, the effect of raising temperature on the sintering degree is not obvious. The coated ANPs show an excellent anti-sinter behavior even when temperature is above their melting point. Different heating rates (1012 K/s–1014K/s) are used to simulate different ignition environments and results show a slow heating rate can make ANPs enter sintering process earlier. For the organic coating layer, carbon and oxygen atoms hinder the formation of the neck region which is an important step in the sintering process. Hydrogen atoms tend to diffuse into the interior of ANPs rather than stay on the surface.