Nanofractography of shocked RDX explosive crystals with atomic force microscopy

Examination with atomic force microscopy has revealed apparent shear-type c leavage steps with heights as small as 0.05 nm, smaller than the size of cy clotrimethylenetrintramine (RDX) molecules, on the fracture surfaces of cry stals that were subjected to aquarium shocks of 61.6 or 129 kbar, both grea ter than the pressure (38 kbar) required for the alpha-to-gamma phase trans formation. The shocked centimeter size, originally transparent crystals bec ame opaque and white from prolific fractures and internal cracks that are a ssociated with their breakup into nanocrystallites of sizes extending from 500 down to 20 nm. The submolecular steps are related geometrically to the macroscale (K-parallel to) fracture mechanics mode of shear fracturing that has obvious consequences at the nanoscale level for nonregistry between mo lecules across the crack surfaces. The results are of interest in relation to lattice trapping of crack fronts and as a contribution to the possibilit y of deformation-induced chemical decomposition/detonations. (C) 2001 Ameri can Institute of Physics.