Oxidation of aluminum nanopowders obtained by electro-exploded wires is studied. Particle size distributions are obtained from transmission electron microscopy (TEM) images. Thermo-gravimetric (TG) experiments are complemented by TEM and XRD studies of partially oxidized particles. Qualitatively, oxidation follows the mechanism developed for coarser aluminum powder and resulting in formation of hollow oxide shells. Sintering of particles is also observed. The TG results are processed to account explicitly for the particle size distribution and spherical shapes, so that oxidation of particles of different sizes is characterized. The apparent activation energy is obtained as a function of the reaction progress using model-free isoconversion processing of experimental data. A complete phenomenological oxidation model is then proposed assuming a spherically symmetric geometry. The oxidation kinetics of aluminum powder is shown to be unaffected by particle sizes reduced down to tens of nm. The apparent activation energy describing growth of amorphous alumina is increasing at the very early stages of oxidation. The higher activation energy is likely associated with an increasing homogeneity in the growing amorphous oxide layer, initially containing multiple defects and imperfections. The trends describing changes in both activation energy and pre-exponent of the growing amorphous oxide are useful for predicting ignition delays of aluminum particles. The kinetic trends describing activation energies and pre-exponents in a broader range of the oxide thicknesses are useful for prediction of aging behavior of aluminum powders.

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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

Magnetic nanoparticles based on iron and its oxides are promising in various biomedical applications. Currently, as a rule, ferromagnetic iron oxide particles with a low specific magnetic moment are used for medical purposes. In the present work, a new method for the synthesis of magnetic nanoparticles based on the electric explosion of a Fe wire is proposed. When wires are dispersed by high current electric pulse in an inert atmosphere containing less than 5% oxygen, nanoparticles with a core-shell structure are formed, where the core is α-Fe and the shell is formed by a mixture of oxides Fe 3 O 4 and FeO. The oxygen concentration in the buffer gas has been found to determine the size of the resulting nanoparticles, their shape, and iron content. The iron oxide shell protects the iron core from the external environment, preventing the rapid dissolution of Fe containing in the nanoparticles, in contrast to nanoparticles obtained in argon atmosphere. The specific magnetic moment of nanoparticles, depending on the content of iron oxides, varies from 90 to 180 emu/g. Keywords Fe-Fe 3 O 4 nanoparticles . Electrical explosion of a wire . Oxidation . Core-shell structures . Magnetic properties