Nanoenergetic Materials: Aluminum/Boron Compound Coated with Perfluoro Plasma Nanofilms

Eugene J. Haley, Prawal P.K. Agarwal, Themis Matsoukas, Chemical Engineering Pennsylvania State University, State College, Pennsylvania, 16802, United States

Aluminum (Al, 31 kJ/g) and Boron (B, 58 kJ/g) are highly energetic metals with numerous applications such as rocket fuels. Nanoparticles are especially beneficial in overcoming kinetic limitations but suffer because a substantial fraction of their mass is already oxidized in the form of a thin native oxide at the particle surface. The oxide layer represents dead weight that decreases the gravimetric energy density of the material and acts as a diffusion barrier that hinders oxidation. One way to minimize these effects is via the synthesis of Al-B compounds. The presence of Al during oxidation leads to an exothermic thermite reaction, which converts boron oxide into highly energetic B by sacrificing less energetic Al. In this study, we develop a facile method to synthesize energetic Al-B composites by annealing a stoichiometric mixture of Aluminum (70 nanometers) and Boron (500 nanometers). We then treat the synthesized composites by plasma deposition of a thin fluorocarbon film in nonthermal plasma to provide passivation and enhance energy release via fluorine reactions with the oxide. We characterize the oxidation and energy release of the material by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) are used to study the composition of the material. High-Resolution Transmission Electron Microscopy (HRTEM), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) are used to analyze the shape, size, and elemental distribution of the synthesized and coated material.