Boron nanoparticles prepared by milling in the presence of a hypergolic energetic ionic liquid (EIL) are suspendable in the EIL and the EIL retains hypergolicity leading to the ignition of the boron. This approach allows for incorporation of a variety of nanoscale additives to improve EIL properties, such as energetic density and heat of combustion, while providing stability and safe handling of the nanomaterials.

No abstract

International audienceA total of 38 ionic liquids (19 of which are new) comprised of 13 cations, 1-propargyl-3-methyl-imidazolium, 1-allyl-3-methyl-imidazolium, 1,3-dimethyl-imidazolium, 1-ethyl-3-methyl-imidazolium, 1-butyl-3-methyl-imidazolium, 1-methoxyethyl-3-methyl-imidazolium, 1-methyl-4-butyl-1,2,4-triazolium, 1-methyl-4-allyl-1,2,4-triazolium, 1-methyl-4-amino-1,2,4-triazolium, N-butyl-N-methyl-pyrrolidinium, N-allyl-N-methyl-pyrrolidinium, N-allyl-pyridinium, and N-butyl-3-methyl-pyridinium, paired with three anions, dicyanamide, azide, and nitrocyanamide, have been prepared, characterized, and evaluated as potential hypergolic fuels by determining key physical, thermal, and ignition properties. The reactivity of these ionic liquids (32 liquids and 6 solids which melt below 100 degrees C) was strongly correlated to increased electron density in the cation, while small changes in physical properties had little effect beyond a certain threshold, suggesting that subtle changes in chemical reactivity can greatly influence the hypergolic ignition pathway

The structure of two different energetic ionic liquids and the nature of their binding to elemental boron surfaces were investigated by a combination of X-ray photoelectron spectroscopy, IR spectroscopy, zeta potential measurements, thermogravimetric analysis, and first-principles theory. It was found that both 1-methyl-4-amino-1,2,4-triazolium dicyanamide ([MAT][DCA]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) ionic liquids bind to boron well enough to resist removal by ultrasonic washing and to protect the boron surface from oxidation during air exposure of the washed powder. The data suggest that both the cation and the anion of the ionic liquids interact with the boron surface; however, for [MAT][DCA], the interaction of the cation appears to dominate, while for [BMIM][DCA] the interaction with the [DCA]− anion dominates. The difference is attributed to the binding of boron to the amino group of [MAT]+, and the amino group also appears to help bind a thicker ionic liquid (IL) capping layer.

Ball milling of boron in an H2 atmosphere was found to result in hydrogen uptake of up to 5% by weight (36 mol %). The nature of the hydrogen binding to boron was probed by a combination of ab initio theory, IR spectroscopy, thermogravimetric analysis, and mass spectral measurements of gases evolved during sample heating. The dominant binding mode is found to be H atoms bound to B atoms in the surface layer of the particles, and the high hydrogen loading results from production of very high surface area, indicating that gaseous H2 is an effective agent promoting size reduction in milling. Hydrogen incorporated in the samples was found to be stable for at least a month under ambient conditions. Desorption is observed beginning at ∼60 °C and continuing as the temperature is increased, with broad desorption features peaking at ∼250 and ∼450 °C, and ending at ∼800 °C. Unprotected hydrogenated boron nanoparticles were found to be reactive with O2 producing a hydrated boron oxide surface layer that decomposed readily at 100 °C leading to desorption of H2O. Hydrogenated boron nanoparticles were found to promote a higher flame height in the hypergolic ignition of ionic liquids upon contact with nitric acid.