Preparation and characterization of cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) powder: Comparison of microscopy, dynamic light scattering and field-flow fractionation for size characterization

RDX powder was prepared using a supercritical anti-solvent (SAS) recrystallization. Then the physicochemical properties of the RDX powder were analyzed by using differential scanning calorimetry (DSC), electrophoretic light scattering (ELS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The size distribution of the RDX powder was studied by dynamic light scattering (DLS) and optical microscopy (OM). Asymmetrical flow field-flow fractionation (AsFlFFF) was tested for determination of size distribution. Results from FFF were compared with those from DLS and OM, and then the merits and limitations of the sizing techniques were discussed. It was found that DLS is not suitable for the size analysis of samples having broad size distributions, such as the RDX powder prepared in this work. The mean sizes of the RDX powder obtained by OM and FFF were in reasonable agreement. For FFF analysis, combination of FL-70, a surfactant, with regenerated cellulose (RC) membrane was found to provide the best performance with good resolution and minimized particle-membrane interaction, resulting in reliable size distribution. The FFF technique showed higher reproducibility in measuring the particle size than OM or DLS with relative standard deviation of 6%. FFF is a useful tool for size-based separation and size characterization of the RDX powder with a particle size distribution from about 1 μm to 25 μm.