Studies on the burning of micro-and nano-aluminum particle clouds

International audienceThe aim of the present work is to reduce the burning time of aluminum particles with the ultimate goal to improve the performances of solid propellants. Aluminium nanoparticles have gained importance because of their increased reactivity as compared with traditional micro-sized particle. Decreasing the size of Al particles increases their specific surface area, and hence decreases the burning time of the same mass of particles. Nevertheless another consequence of decreasing the particle size is an increase of alumina mass fraction in the reactant powders passivated in air. An experimental program is initiated to determine flame propagation velocities of micro-sized (around 6 µm) and nano-sized (around 250 nm) aluminum particle clouds. Another goal of this study is to estimate the gas phase temperature from AlO molecular spectra and the temperature of condensed phase emitters in the flame using emission spectroscopy. To this end, an experimental setup is developed to investigate the flame characteristics of particle clouds ignited by an electric spark in a glass tube. The present results show that nano-sized Al particle clouds burn faster than micro-sized particle clouds for the same global particle mass concentration in air. The cloud flame propagation velocity depends also on the particle concentration. The temperature measurements indicate a consistent value around 2900 K for all nano-Al particle burning clouds and 3300 K for micro-Al particle clouds. The results of the condensed phase temperature show, first a stable temperature and then a decreasing trend along the axis of the flame