Topographic Investigations of Various HMX Grades

Three HMX grades, a standard, a high-purity and a reduced sensitivity grade, were investigated using 3D imaging with confocal microscopy and ion milling. The standard and high-purity grades showed euhedral particles, but also intergrown crystal domains, twinning, and surface steps. Besides local defects were characterized on the surface and in the bulk, such as outgrowths, ditches, grain boundaries or microcavities. The investigations revealed high outgrowth concentration on standard grade crystals compared to the high-purity grade. The RS-HMX variant showed different crystal shapes with rounded edges and corners 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, e.g., to reduce delamination during mechanical loading or aging. Future approaches to spherical particles may aim on further reduced viscosities, increased solid loads and performance of plastic bonded explosives.