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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

Nanoaluminum powder (nAl, nominal size of particles 50 nm and 100 nm), obtained by electrical explosion of wires, was passivated by air and coated by several different protective organic reagents to assess the effects on ballistics of nAl-loaded hydroxyl-terminated polybutadiene (HTPB)-based solid fuel with respect to pure HTPB baseline. The nAl samples were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and chemical analysis on active aluminum content (Al°) content and added to HTPB-based solid fuels for hybrid propulsion. Combustion tests were carried out burning central-perforated single-port cylindrical samples in a 2D radial burner. Data analysis was performed to obtain a continuous time-resolved regression rate. Coated nAl particles may significantly improve the ballistics of HTPB + nAl formulations burning in gaseous oxygen, with respect to pure HTPB. All investigated formulations with nAl exhibit increase of instantaneous regression rate (up to 89% maximum), depending on coatings and oxidizer mass flux G ox . Fluoroelastomer and fluorine-containing chemicals used for coating show a good compromise between increase in regression rate and low sensitivity to G ox variation under the implemented operating conditions

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