Abstract
Mono-dispersed, spherical and core/shell structure aluminum nanopowders (ANPs) were produced massively by high energy ion beam evaporation (HEIBE). And the number weighted average particle size of the ANPs is 98.9 nm, with an alumina shell (3–5 nm). Benefiting from the passivation treatment, the friction, impact and electrostatic spark sensitivity of the ANPs are almost equivalent to those of aluminum micro powders. The result of TG-DSC indicates the active aluminum content of ANPs is 87.14%, the enthalpy release value is 20.37 kJ/g, the specific heat release S1/Δm1* (392–611 °C) which determined the ability of energy release is 19.95 kJ/g. And the value of S1/Δm1* is the highest compared with ANPs produced by other physical methods. Besides, the ANPs perfectly compatible with hydroxyl-terminated polybutadiene (HTPB), 3 wt. % of ANPs were used in HTPB propellant replaced micron aluminum powders, and improved the burning rate in the 3–12 MPa pressure range and reduced the pressure exponential by more than 31% in the 3–16 MPa pressure range. The production technology of ANPs with excellent properties will greatly promote the application of ANPs in the field of energetic materials such as propellant, explosive and pyrotechnics.
Highlights
The large specific surface area, high density, low consumption of oxygen, high volumetric heat of combustion and high reactivity made aluminum nanopowders (ANPs) can be broadly used in propellants[1, 2]
ANPs can be prepared using a variety of techniques, including electro-exploded wire (EEW)[14, 15], plasma synthesized process[16, 17], sol–gel[18], induction heating evaporation (IHE), laser-induction complex heating evaporation (LCHE)[19]
The reactivity of ANPs, which characterizes their behavior in oxidized media was determined by four parameters which can be directly obtained from DTA (DSC) and TG curves[12, 22,23,24]: (1) The temperature for the onset of intensive oxidation (Ton, °C), (2) The maximum rate of oxidation (Vox, mg/min), (3) The degree of conversion of Al in a certain range of temperatures (α, %), (4) The ratio of the oxidation thermal effect (S/Δm*, kJ/g)
Summary
The large specific surface area, high density, low consumption of oxygen, high volumetric heat of combustion and high reactivity made ANPs can be broadly used in propellants[1, 2]. The burning rate of propellants can be increased by employing aluminum powders with higher specific surface area[8, 9]. Replacement of micro-aluminum powders by ANPs will increase the propellant burning rate by ~100% and always show low pressure-exponents in 1–12 MPa pressure range[10]. The high reactivity of ANPs have caused aging problems, in an environment of high relative humidity[11] Another problem of using ANPs as additives in propellants is the original agglomeration, leading to heterogeneity of the mixtures and to coalescence of agglomerates in the heat penetration zone during combustion[12]. Characterization of ANPs includes the particle diameters, dispersion and morphology, structure, oxide layer thicknesses, thermal behavior. The reactivity of ANPs, which characterizes their behavior in oxidized media was determined by four parameters which can be directly obtained from DTA (DSC) and TG curves[12, 22,23,24]:
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