Characterization and Combustion of Aluminum Nanopowders in Energetic Systems

Following a comprehensive literature survey about use of Al nanopowders in a range of HEM applications — including rocket propulsion, pyrotechnics, and explosives - a through treatment is offered of the ideal and delivered thermochemical performance of the most interesting metallic ingredients to augment solid and hybrid rocket propulsion. The particular but fundamental class of nAl powders is then investigated in detail: critical issues such as coating and characterization of the powders, rheological and mechanical properties, combustion and ballistic behavior are all examined under a variety of operating conditions. Although attractive for fundamental studies and much used in laboratory experiments, no rocket propulsion operational systems are yet reported in use for nAl powders. Loss of active metal, cold cohesion, and poor propellant castability globally overcome advantages such as increased burning rate (easily achievable by other ways) and reduced specific impulse losses associated with 2P flow (thanks to less agglomeration with respect to the corresponding micrometric powders). Use of dual metallic fuels, by properly blending μAl and nAl, and/or modification of the natural properties of nAl particles, by suitable coatings, represent two possible ways to exploit the potential of nanopowders. Several approaches are also discussed so as to improve dispersion and mechanical properties of solid propellants or solid fuels containing nAl. Overall, a good control of particle size, metal content, and dispersion is a crucial requirement for successful applications of nanoingredients in propulsion.