Characterization and Combustion of Aluminum Nanopowders in Energetic Systems

Abstract

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

Progress in Additive Manufacturing of Energetic Materials: Creating the Reactive Microstructures with High Potential of Applications

“…The structure, combustion and application of energetic systems based on fine, submicron and nanosized metals (in addition to changes in the names of these materials with time) were investigated extensively by the author's group [38,[152][153][154][155][156][157], as well as by other teams of researchers [158][159][160][161][162][163][164]. The most prominent result observed was the decrease in the ignition time and increase in the burning rate for compositions containing nano-Al [38,155,156].…”

“…The most prominent result observed was the decrease in the ignition time and increase in the burning rate for compositions containing nano-Al [38,155,156]. However, the wide utilization of nanometals is limited by several factors, i. e., (i) the reduced metal content and associated performance losses [160] (note the surprising positive effect of the oxide layer [165]), (ii) stability issues, e. g., oxidation during storage [166], (iii) coalescence prior to reaction, diminishing the effects of nanosize [167,168], (iv) the gradual increase in viscosity for compositions with a binder [169], and (v) the difficulty of obtaining a uniform composite mixture with nanocomponents [156,170].…”

Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

“…m f . In spite of differences in the combustion mechanism of polymeric and liquefying fuels, both kinds of formulations can achieve increased ballistic performance thanks to the use of metal-based energetic additives [15][16][17][18][19].…”

“…Nano-sized Al is characterized by SSA~10 m 2 /g (or higher, depending on the average powder particle size and size distribution). These powders show marked reactivity at temperatures lying below the Al melting point (933 K) [17,34,35,40]. Nano-sized Al is typically passivated by air, although special chemicals may be used to shield the metal from the external environment [34,35,40].…”

“…The presence of metal additives, including Al, implies the possible insurgence of performance losses due to incomplete metal combustion, two-phase flow expansion, and residual accumulation Aerospace 2019, 6, 127 3 of 33 in the combustion chamber/nozzle walls [17][18][19][20][21][22]. All these issues are of particular relevance in HRE combustion due to the diffusion-limited mechanism and the relatively low combustion efficiency of these systems.…”