Combustion behaviors of bimodal aluminum sizedistributions in thermites

Abstract

In recent years many studies that incorporated nano-scale or ultrafine aluminum (Al) as part of an energetic formulation demonstrated significant performance enhancement. Decreasing the fuel particle size from the micron to nanometer range alters the material¡¦s chemical and thermal-physical properties. The result is increased particle reactivity that translates to an increase in the combustion velocity and ignition sensitivity. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composite of Al and molybdenum trioxide (MoO3) at the theoretical maximum density (TMD) of a loose power (5% TMD) and a compressed pellet (50% TMD). A bimodal Al particle size distribution was prepared using 4 or 20 ƒÝm Al fuel particles that were replaced in 10% increments by 80 nm Al particles until the fuel was 100% 80 nm Al. These bimodal distributions allow the unique characteristics of nano-scale materials and their interactions with micron scale Al particles to be better understood.