Oxide-Free, Catalyst-Coated, Fuel-Soluble, Air-Stable Boron Nanopowder as Combined Combustion Catalyst and High Energy Density Fuel

Abstract

Elemental boron has one of the highest volumetric heats of combustion known and is therefore of interest as a high energy density fuel. The fact that boron combustion is inherently a heterogeneous process makes rapid efficient combustion difficult. An obvious strategy is to increase the surface area/volume ratio by decreasing the particle size. This approach is limited by the fact that boron forms a ∼0.5 nm thick native oxide layer, which not only inhibits combustion, but also consumes an increasing fraction of the particle mass as the size is decreased. Another strategy might be to coat the boron particles with a material (e.g., catalyst) to enhance combustion of either the boron itself or of a hydrocarbon carrier fuel. We present a simple, scalable, one-step process for generating air-stable boron nanoparticles that are unoxidized, soluble in hydrocarbons, and coated with a combustion catalyst. Ball milling is used to produce ∼50 nm particles, protected against room temperature oxidation by oleic acid functionalization, and optionally coated with catalyst. Scanning and transmission electron microscopy and dynamic light scattering were used to investigate size distributions, with X-ray photoelectron spectroscopy to probe the boron surface chemistry.