Characterizing the Fate and Toxicity of a Nanotechnology after Use: Nano-Aluminum Thermite Formulations

A.J. Kennedy, A. Poda, R. Moser, A.J. Bednar, S.F. Son, J.A. Steevens
US Army Engineer Research and Development Center, US

Keywords: nano, toxicity, thermite, nanotechnology, environmental release

Summary:

Environmental testing of nanomaterials has focused primarily on free nanoparticles. Fewer studies address the implications of nanotechnologies. We consider high efficiency energetic materials called nanothermites. Propellants and explosives employing nanothermites are freely dispersed particle technologies with obvious release potential. Nanothermites are commonly nano-aluminum (Al) particles mixed with catalysts (nano-metal oxides). Characterization of pre- and post-combusted nanomaterials and residues indicated the combustion residue was sintered into large aggregates. Expended Al/Fe2O3 formulations comprised of particles >75 μm, whereas Al/Bi2O3 formulations yielded smaller (<5 μm) particles. Residues settled quickly, suggesting low potential for transport. The implications of nano Al2O3/CuO nanothermite residues (using spheres and rods) were further investigated due to the well established toxicity of Cu. Results indicated that while CuO spheres were more stable, rods released more ions and were more toxic to Ceriodaphnia dubia; toxicity expression by surface area improved dosimetry. While residue aggregates were much less stable than the CuO reactant nanoparticle, toxicity increased related to the redox state the Cu. Results emphasize importance of considering the implications of nanoparticles in context with their use and provide opportunity for green engineering (use of alternative metal catalysts with lower implications).