ABSTRACT

A technique of Rapid Expansion of Supercritical Solutions (RESS) to produce nano-crystalline energetic materials was developed and characterized in application to production of nano-scale crystals of cyclotrimethylene-trinitramine (RDX). Nano-crystals of RDX were formed by expansion of supercritical solutions of RDX in carbon dioxide through a 100 μm sapphire nozzle at initial pressures of 150−295 bar and temperatures of 323−363 K. Produced particles were characterized by Field Emission Scanning Electron Microscopy, X-ray diffraction, HPLC, and melting point analysis. The process produced particles with the mean size in the range of 110 - 300 nm with a narrow size distribution.
The product was crystalline, as determined by X-ray diffraction. The effect of process conditions (T, P) on the crystal size distribution was determined. Initial impact sensitivity tests (performed with an ERL, Type 12 impact tester) were performed and compared with the sensitivity of the original (micron scale) material.
In addition to the characterization of the final particles produced by RESS, a technique to monitor particle growth in situ along the supersonic expansion jet was developed and applied to the RESS jet. The technique, based on UV pulsed laser imaging using a gated ICCD camera, allows direct measurements of the particle size distribution down the expanding jet. The same experimental approach utilizing two separated pulses from two lasers is used to characterize the velocity field after the nozzle.