Dissolution of microscale energetic residues in saturated porous media: visualization and quantification at the pore-scale by spectral confocal microscopy.

Microscale energetic residues (<1 mm) are produced during munitions detonation and the weathering of larger residues, and may serve as mobile and fast dissolving sources of explosive compounds, such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Knowledge of the behavior of microscale energetic residues in subsurface environments is quite limited. This work employed a previously unreported property of TNT, RDX, and HMX (i.e., autofluorescence under 405 nm laser illumination) to visualize and quantify the dissolution of microscale physically attrited energetic residues in saturated porous media. The results demonstrated that within the Composition B particles, TNT dissolved preferentially over RDX/HMX and the mass ratio of RDX/HMX to TNT increased by >5.3 times initially. The focused particles dissolved in a stepwise fashion, with >72% of particle volume reduction in <36 min. Moreover, the results suggested that the particle shape factor was relatively stable and the particles retained their highly irregular shape throughout the dissolution processes. This is the first work to demonstrate application of spectral confocal microscopy for visualizing and quantifying the behavior of energetic residues at the pore-scale.