Synthesis and characterization of coated energeticmaterials using a RESS-N system

Coating nano-sized aluminum particles with an energetic material such as RDX has several unique advantages. The RDX coating can protect the aluminum surface from developing a growing oxide coating and can potentially improve performance by bringing the two components into closer contact than would conventional mixing. In this investigation, a custom-built rapid expansion of a super-critical solution with a nonsolvent (RESS-N) system was modified to coat nano-sized aluminum (ALEX^® ) particles. Particles were coated by entraining them in a solution of supercritical CO₂ and RDX and then rapidly expanding the mixture through a nozzle. To achieve this, a particle entrain- ment vessel introduced ALEX^® particles into the flow and the suspension was flown through a micro-orifice sapphire nozzle. The rapid expansion of the supercritical solution and the addition of ALEX^® particles as nucleation sites created favorable conditions for the RDX to coat the ALEX^® particles by heterogeneous nucleation. Tests were run at pre-expansion pressures up to 34.5MPa and pre-expansion temperatures up to 353 K. Particles were successfully coated with RDX and collected by expanding the CO₂ until it formed dry ice, which allowed for gravimetric collection. The success- ful coating of the particles was confirmed by field emission scanning electron microscopy (FE-SEM). Environmental scanning electron microscopy (ESEM) with energy disperse spectroscopy (EDS) was used to confirm that only RDX and ALEX^® particles were collected and that the coating material was truly RDX.