Arrested reactive milling synthesis and characterization of sodium-nitrate based reactive composites

Arrested reactive milling was used to synthesize three composite powders using sodium nitrate as an oxidizer, and magnesium, aluminum, and mechanically alloyed aluminum-magnesium (Al-0.5 Mg-0.5) as respective fuels. Both magnesium and aluminum powders formed flakes with varying thickness from hundreds of nm to several mu m sandwiched between sodium nitrate particles. Three-dimensional composite and nanocomposite particles were formed with Al-Mg mechanically alloyed powder. No change in the crystallinity of any components was observed from X-ray diffraction patterns of the composite materials. Materials were characterized using differential thermal analysis (DTA) and simultaneous thermogravimetry (TG), carried out in argon. In composite materials, the decomposition of sodium nitrate starts at lower temperatures than for pure sodium nitrate. Weight loss is observed to start at relatively low temperatures. The most significant exothermic events occur at substantially higher temperatures, and therefore in a material that may have been significantly altered from its initial state. The results of thermal analysis indicate that the composite with mechanically alloyed Al-Mg powder is most stable at low temperatures. Ignition of the prepared composites was studied using a thin layer of powder coated on an electrically heated filament. These experiments showed that the composite with mechanically alloyed Al-Mg powder ignites at lowest temperatures and thus is expected to have the shortest ignition delays in practical applications. The emission spectra of the prepared composites burning in air are presented.