Characterization and differentiation of aluminum powders used in improvised explosive devices – Part 1: Proof of concept of the utility of particle micromorphometry

Abstract

This is publication number 20-64 of the Laboratory Division of the Federal Bureau of Investigation (FBI). The views expressed are those of the authors and do not necessarily reflect the official policy or position of the FBI or the U.S. government. Names of commercial manufacturers are provided for identification purposes only, and inclusion does not imply endorsement of the manufacturer or its products or services by the FBI.

Characterization and differentiation of aluminum powders used in improvised explosive devices. Part 2: Micromorphometric method refinement and preliminary statistical analysis

“…The microscope was set up for proper Köhler illumination. A NIST‐traceable stage micrometer was used for linear calibration and polystyrene spheres covering the sample size range were used for measurement validation as reported in Baldaino et al [4]. Using this system, 200 random FOVs from each coverslip were captured digitally [4] (see Figure 3).…”

“…A NIST‐traceable stage micrometer was used for linear calibration and polystyrene spheres covering the sample size range were used for measurement validation as reported in Baldaino et al [4]. Using this system, 200 random FOVs from each coverslip were captured digitally [4] (see Figure 3). Prior to the analysis of Al powder extracted from spray paints, the default automatic image thresholding criteria for detecting dark objects on a brightfield background were used to set the background threshold parameters in Image‐Pro Plus ® [12].…”

“…In previous statistical analyses of Al powder micromorphometric data, it was necessary to reduce the number of parameters due to computational limitations [4]. However, for the current analysis, it was desirable to use all available micromorphometric parameters in an attempt to discriminate between different Al powder sources using LDA.…”

“…Of the 14 sources, nine were produced from ball-milled Al foil and five were extracted from spray paint. First, the automated image analysis methods described in Baldaino et al [4] were used to obtain quantitative micromorphometric features from particles in 200 randomly selected FOVs from each coverslip (18 mm × 18 mm). This resulted in data for 17 micromorphometric parameters for thousands of particles collected from 420 coverslips (aliquots).…”

“…In addition, all previously analyzed samples [4] for which there was sufficient remaining sample were reanalyzed in this manner.…”