Asymmetrical Flow Field-Flow Fractionation for Characterization of Cyclotrimethylene Trinitramine (RDX) Particles Prepared by Supercritical Anti-Solvent Recrystallization

In this work, asymmetrical flow field-flow fractionation (AsFlFFF) was employed to determine the mean diameters and size distributions of cyclotrimethylene trinitramine (RDX) particles. The micro-particles of RDX were prepared using a supercritical anti-solvent recrystallization process. The influence of the spraying method, i.e., the pressure drop generated during the spraying of the RDX solution into the supercritical carbon dioxide (CO2) phase, on the size and shape of the recrystallized RDX particles, was investigated. It was found that the mean diameter of the recrystallized RDX particles decreased as the pressure drop increased, mainly due to the reduction in the population of larger particles. Also, the size distribution tended to become narrower with increasing pressure drop for the same reason. Near-spherical RDX particles with a relatively narrow size distribution were obtained at a pressure drop of 11 MPa. The mean diameters of the RDX particles determined by AsFlFFF were in reasonable agreement with those obtained by optical microscopy (OM). The AsFlFFF seems to be a useful tool for the separation and characterization of RDX particles.