(96d) B-C and B-Fe Core-Shell Nanoparticles for the Enhancement of Biofuel Combustion

Liquid biofuels such as ethanol are good candidates to partially replace fossil fuels. However, the adoption of biofuels is inhibited by low energy densities and incomplete combustion. These characteristics are problematic for applications with a high energy demand, such as ramjets. Boron additives are a promising solution because they are among the most energy-dense materials. Boron can increase the overall heat release of the fuel and reduce its ignition temperature. However, boron gradually oxidizes when stored under ambient conditions, may not completely burn, and the used metal particles lack recyclability and are subject to environmental regulations. These problems are less limiting in ramjets and other specialty combustion applications.

In this study, we synthesized core-shell Boron-Carbon (B-C) and Boron-Iron (B-Fe) nanoparticles for the combustion of ethanol. A variety of templated, non-templated, and wet-chemical techniques were used to produce elemental boron (zero valent) with either a carbon or iron shell. The composites were characterized by N₂ Physisorption, TGA/DSC, ICP/AES, XRD, SEM/EDX, TEM, and SAXS. The composites had surface areas from 20-150 m²/g, pore sizes from 5-40 nm, and shell thicknesses between 5-20 nm. Boron was well-distributed and mostly amorphous, indicating that reactions with iron or carbon were minimal. The combustion properties with ethanol were determined through batch combustion in a calorimeter. The B-C and B-Fe composites lowered ignition temperatures and raised the rate of fuel conversion in almost all cases. The best B-C composites were synthesized with polymer templates and had relatively large shell thicknesses and pore sizes that positively affected oxygen transport. The best B-Fe composites could be broken down into smaller particles, which is beneficial when fluidized in a ramjet combustor.