Enhanced Energetic Performance of Aluminum Nanoparticles by Plasma Deposition of Perfluorinated Nanofilms

Abstract

The performance of Al as nanoenergetic material in solid fuel propulsion or additive in liquid fuels is limited by the presence of the native oxide layer at the surface, which represents a significant weight fraction, does not contribute to heat release during oxidation, and acts as a diffusion barrier to Al oxidation. We develop an efficient technique in which the oxide layer is effectively turned into an energetic component via a reaction with fluorine that is coated in the form of a fluorocarbon nanofilm on the Al surface by plasma-enhanced chemical vapor deposition. Perfluorodecalin vapors are introduced in a low-pressure plasma reactor to produce nanofilms on the surface of Al nanoparticles, whose thickness is controlled with nanolevel precision as demonstrated by high-resolution transmission electron microscopy images. Coated particles show superior heat release, with a maximum enhancement of 50% at a thickness of 10 nm. This significant improvement is attributed to the chemical interaction between Al2O3 and F to form AlF3, which removes the oxide barrier via an exothermic reaction and contributes to the amount of heat released during thermal oxidation. The chemistry and mechanism of the enhancement effect of the plasma nanofilms are explained with the help of X-ray photoelectron spectroscopy, X-ray diffraction, high-angle annular dark-field scanning transmission electron microscopy–energy dispersive spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

Engineered Surface Chemistry and Enhanced Energetic Performance of Aluminum Nanoparticles by Nonthermal Hydrogen Plasma Treatment

“…The effect became saturated after 6 min, and not a significant enhancement was observed at 8 min of HP treatment. Figure b shows the HRTEM image of oxidized untreated Al particles in which hollow shells are observed due to the expansion and transport of liquid Al through oxide shells to undergo oxidation, which is a common observation in the literature. , Al false( normalOH false) 3 false( normals false) + 3 H → Al false( normals false) + 3 H 2 O false( normalg false) ; ⁣ Δ G ° = − 3562.2 kJ / mol …”

“…Table summarizes the data presented in Figure a and Figure c. The amount of Al oxidized is calculated from the weight gain measured by TGA . The amount of Al oxidized increases systematically with the treatment time in the plasma.…”

Low-Temperature Cost-Effective Synthesis of MgB2 for Energetic Applications

“…Metal-based energetic materials are quite attractive due to their ability to store a significant amount of chemical energy that can be released by oxidation and can be used in several applications, including batteries, fuel cells, rocket propellants, and solid ramjet fuels. − The combination of metals such as aluminum and magnesium with boron in the form of their borides can be very effective because of the high energy density of boron and the rich chemistry and chemically tunable properties of such materials. In March 2001, Cava, in his article “Genie in a bottle,” quoted“an overlooked compound (MgB 2 ) has a surprise in store for the physicists” after the discovery of the superconducting nature of MgB 2 by Akimitsu and colleagues that could solve the mysteries of high-temperature superconducting materials.…”

“…MgB 2 has been regarded as an interesting candidate for energetic materials as it can store and release a large amount of chemical energy (40 kJ/g), − which lies between the gravimetric energy density of Mg (25 kJ/g) and B (58 kJ/g). At the same time, MgB 2 is thermally and chemically more stable than Mg or B; − hence, it can help store energy for extended periods. Unlike metal particles, a lower concentration of native oxide is present on the surface of MgB 2 because of the unavailability of Mg or B to form bonds with oxygen.…”

“…MgB 2 decomposes into Mg and B at elevated temperatures, which subsequently react with oxygen to form ternary oxides of Mg and B. This avoids the accumulation of B 2 O 3 , which, as a low-temperature melting oxide (450 °C), forms a molten layer that clogs pores and promotes aggregation and sintering during the oxidation of B, thereby delaying the process and reducing its energy output. − ,− …”