Boron Nanoparticle-Rich Fuels for Gas Generators and Propellants

This study reports on the production and characterization of energetic polymer-capped boron for solid fuel applications. It is known that the addition of metal and metal-like particles to solid fuels and propellants can improve the performance of both rocket and air-breathing propulsion systems. The use of boron is very attractive for these applications due to its high heat of combustion on both a gravimetric (58 kJ/g) and volumetric (136 kJ/cm3) basis. However, the exploitation of the high theoretical energy of boron has been limited by a few undesirable properties of this metal. Among them, one notes the existence of a resilient oxide layer on the particle surface affecting the ignition and combustion of boron particles. The capping of boron nanoparticles with a polymer can provide a solution to the aforementioned problem. The use of an energetic polymer for that purpose can bring additional heat close to the surface of the nanoparticles and facilitate their ignition. In the present work, boron nanoparticles were produced by synthesis of surface-functionalized boron. The route was adapted to obtain additional hydroxyl-functional groups on the particles. These hydroxyl sites were used to graft a diisocyanate, and then produce an energetic polymer matrix based on polyurethane chemistry by addition of glycidyl azide polymer, resulting in boron nanoparticles coated by energetic polymers. This can lead to significantly enhanced boron particle combustion.