Optimization of a High-Energy Ti–Al–B Nanopowder Fuel

Abstract

Sonochemically generated reactive metal nanopowders containing Ti, Al, and B represent a new class of high-energy-density nanopowder fuels with superior energy content and air stability as compared to nano-aluminum. In this work, we optimize the energy density of a Ti–Al–B reactive metal nanopowder fuel by varying the Ti:Al:B ratios using a sonochemically mediated decomposition of a complex metal-hydride. After heating the recovered solids under vacuum to temperatures in the range between 150 to 300 °C, the powder’s air stability is significantly improved so that it can be handled in air. Variable-temperature vacuum heat treatment was used to produce fuels tuned to be stable with a gravimetric energy density exceeding that of pure bulk Al (>31 kJ/g). The density of the powder was found to be 2.62 g/cm3 by helium pycnometry, which translates to an impressive volumetric energy content of 89 kJ/cm3. In poly­(methyl methacrylate)-protected bomb calorimetry tests commercial nano-aluminum (SkySpring Nanomaterials, 20% oxide) only produced 25 kJ/g, while the sonochemically generated Ti–Al–B nanopowders released 24% more energy per unit mass and 19% more energy per unit volume in identical experiments.

Effects of Amorphous Ti–Al–B Nanopowder Additives on Combustion in a Single-Cylinder Diesel Engine

“…Fuels. RMNPs were synthesized using sonochemical reaction methods previously described in detail [16,20,21], thus only a brief description is provided here. Both LiAlH 4 (LAH) and LiBH 4 (LBH) are dissolved in diethyl ether (Et 2 O) and slowly added to a reaction flask containing TiCl 4 also dissolved in Et 2 O.…”

“…Reaction stoichiometry can be controlled to produce RMNPs with various Al:B ratios; for this work, the product RMNPs were tuned to contain approximately 20 at % each Ti and B, and approximately 10 at % Al, as well as 20 at % H, 10 at % C, with the balance being Li and Cl. The elemental composition was determined using combustion gas analysis and inductively coupled plasma-optical emission spectroscopy [16]. RMNPs treated at 150 C typically have energy content, as determined by bomb calorimetry, of approximately 30 kJ/g or 75 kJ/cm 3 , although higher energy content has been retained in some cases [16].…”

“…The elemental composition was determined using combustion gas analysis and inductively coupled plasma-optical emission spectroscopy [16]. RMNPs treated at 150 C typically have energy content, as determined by bomb calorimetry, of approximately 30 kJ/g or 75 kJ/cm 3 , although higher energy content has been retained in some cases [16]. Finally, a cryogenic ball mill is used to grind the larger flakes into nanoscale particles.…”

“…The same procedure was used to create suspensions of commercial nano-Al powder (purchased from SkySpring) in JP-5, with the same surfactant fraction. The nano-Al powder used contained 80.7% active metal content, as determined by bomb calorimetry, with the remainder already oxidized [16]. Similar to the RMNPs, DLS measurements showed that the nano-Al powder has a narrow size distribution with average particle diameter of approximately 370 nm.…”

“…We have taken a novel approach to creating nanoparticles with high energy content and favorable combustion characteristics. Using a sonochemical synthesis process, we have developed mixed-metal materials that incorporate Ti, Al, and B into amorphous nanoparticles, and after low-temperature heat treatment at 150 C under vacuum, these RMNPs are highly air-stable and can have energy content as high as 34 kJ/g or 85 kJ/cm 3 [16]. Furthermore, we have shown these RMNPs to combust well when entrained in a methane-air flow in an aerosolized-powder burner [17] and when suspended in decane in a liquid-fuel spray burner [18,19].…”