Aluminum Nanocomposite Materials for Propellant Applications

S.W. Chung, S.W. Buckner, P.A. Jelliss, G.J. Place, J.M. Laktas
nanoMetallix,
United States

Keywords: nanoparticles, solid propellant, nanoenergetics, combustion

Summary:

Aluminum has high applicability in terms of energy release with one of the highest combustion enthalpies of all reactive metals. Thus, the use of aluminum complexes and nanomaterials has been widely researched to develop fuel or fuel additives containing high energy content. However, this high reactivity is also the source of aluminum’s practical difficulties. Traditional aluminum particles are known to be reactive in ambient conditions and in water, thereby forming an oxide layer that limits the applied effectiveness, efficiency, and utility of such nanomaterials. The majority of aluminum research has focused on particles in the micron range that are typically covered in an oxide shell (alumina). Previous research describes the mechanisms by which alumina-coated composites combust, all of which struggle with thermochemical and kinetic properties. Proactively, this reactive strength also proves to be the key to harnessing aluminum's elemental energy. nanoMetallix has developed a new class of engineered particles as novel energetics for integration in advanced propulsion, deflagration, and detonation technologies. We have produced aluminum nanoparticles that prevent conventional oxide layer formation, contain up to 99% active aluminum, and can be produced at and below 10 nm in diameter (orders of magnitude smaller than conventional compounds). This breakthrough is a result of over a ten years of directed research in collaboration with the United States Air Force nanoEnergetics Program. nanoMetallix methods provide a low cost bottom-up approach to synthesizing aluminum nanoparticles. Our compounds are uniquely passivated, utilizing novel “caps” for intimate binding to high-energy oxidizers and other advanced energetic materials. The result is a nanoscale material that prevents oxide layer formation, circumventing the traditional combustion efficiencies presented by leading nanocomposites; employing these novel characteristics will revolutionize thrust capabilities and significantly decrease mass requirements by ~45%. Burn rate analysis revealed an increase of ~60% when compared to commercial nanoaluminum. This vast increase in burn rate leads to rapid temperature rise and gas expansion, and subsequently increased specific impulse. Furthermore, the absence of an oxide layer as shown by DSC/TGA data results in a significant reduction in ignition temperature to ~300°C. nanoMetallix compounds are highly tailorable with regard to particle diameter, capping agent, and binding to functional groups. With this potential for customization in mind, we are now able to deliver energetic materials tailored toward a specific, purpose-driven formulation. This allows us to reverse the traditional mindset of designing propulsion systems, explosives, and weapons systems based to the limitations of standard technology. Simply put, we have made energy smaller, harnessing the pure elemental energy of aluminum on the nanoscale.