Boron Nanoparticles with High Hydrogen Loading: Mechanism for B-H Binding, Size Reduction, and Potential for Improved Combustibility and Specific Impulse.

摘要

Ball milling of boron in an H2 atmosphere was found to result in hydrogen uptake of up to 5 % by weight (36 mole %). 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 approximately 60 deg and continuing as the temperature is increased, with broad desorption features peaking at approximately 50 deg and approximately 450 deg C, and ending at approximately 800 deg C. Unprotected hydrogenated boron nanoparticles were found to be reactive with O2 producing a hydrated boron oxide surface layer that decomposed readily at 100 deg 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.