Surface structures of HMX crystals investigated by means of confocal and atomic force microscopy

Abstract. Three HMX grades - a standard, a high-purity and a reduced sensitivity grade - were investigated using 3D imaging with confocal and atomic force microscopy. The standard and high-purity grades showed euhedral particles, i.e. with well grown faces, edges and corners, but also, intergrown crystal domains, twinning, and surface steps. Besides local defects were characterized on the surface, such as outgrowths, ditches, grain boundaries or microcavities, and outgrowth concentrations were quantified at various high levels. The investigations revealed high concentrations on standard grade crystals compared to the high purity grade. The RS-HMX variant showed a different picture of crystal shapes still far from spherical but with rounded edges and corners and without surface outgrowths. Such particle surfaces without sharp structures may help reducing the sensitivity of explosive particles and the viscosity of particle binder mixtures, whereas a moderate roughness supports a proper binder particle adhesion.