Proceedings Article | 22 May 2015
KEYWORDS: Particles, Explosives, Glasses, Photomicroscopy, Microscopes, Optical spheres, Image segmentation, Aluminum, Humidity, Microscopy
When handling explosives, or related surfaces, the hands routinely become contaminated with particles of explosives and
related materials. Subsequent contact with a solid surface results in particle crushing and deposition. These particles
provide an evidentiary trail which is useful for security applications. As such, the opto-physico-chemical characteristics
of these particles are critical to trace explosives detection applications in DOD or DHS arenas. As the persistence of
these particles is vital to their forensic exploitation, it is important to understand which factors influence their
persistence. The longevity or stability of explosives particles on a substrate is a function of several environmental
parameters or particle properties including: Vapor pressure, particle geometry, airflow, particle field size, substrate
topography, humidity, reactivity, adlayers, admixtures, particle areal density, and temperature. In this work we
deposited particles of 2,4-dinitrotoluene on standard microscopy glass slides by particle sieving and studied their
sublimation as a function of airflow velocity, areal particle density and particle field size. Analysis of 2D microscopic
images was used to compute and track particle size and geometrical characteristics. The humidity, temperature and
substrate type were kept constant for each experiment. A custom airflow cell, using standard microscopy glass slide,
allowed in-situ photomicroscopy. Areal particle densities and airflow velocities were selected to provide relevant
loadings and flow velocities for a range of potential applications. For a chemical of interest, we define the radial
sublimation velocity (RSV) for the equivalent sphere of a particle as the parameter to characterize the sublimation rate.
The RSV is a useful parameter because it is independent of particle size. The sublimation rate for an ensemble of
particles was found to significantly depend on airflow velocity, the areal density of the particles, and the particle field
size. To compare sublimation studies these parameters must be known.
