Sieve stack and laser diffraction particle size analysis of IMX-104 low-order detonation particles

Abstract

When an artillery round undergoes a low-order detonation during live-fire training or an unexploded ordnance clearance operation, up to 25% of the round's energetic contents are scattered over a small, localized area, sometimes less than 100 m 2. Training-range fate and transport models require an accurate representation of the particle-size characteristics of the material left behind from low-order detonations. This study investigated using laser diffraction particle size analysis to characterize 26 samples collected from four low-order command-detonated 81 mm mortar bodies filled with IMX-104. The refractive index of IMX-104 was estimated using an iterative recalculation technique on a Horiba LA-960 that yielded 1.845 0.01i. Of the 25 triplicate analyses conducted using this value, 12 passed the USP <429> measurement standard with 9 of the remaining samples found to have had a reduction in particle size during analysis that caused artificially high coefficient of variance values. The cumulative percent of particle sizes determined by laser diffraction and sieve stack differed by 0%-21.9% (median = 0.2%-7.2%). In addition, the higher resolution results of the laser diffraction particle size analysis, especially for particles smaller than 0.5 mm, make it the preferred method of analysis. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

Determination of residual low-order detonation particle characteristics from Composition B mortar rounds

“…The particles from these studies were characterized using sieving from >12.5 to <0.25 mm. As part of Strategic Environmental Research and Development Program (SERDP) ER-2219, LO detonations were initiated using small masses of C-4 plastic explosive in a fuze simulator that replaced the standard-issue fuze on 81 mm mortar rounds filled with IMX-104 (an insensitive munition formulation containing RDX, 3-nitro-1,2,4-triazol-5-one, and 2,4,-dinitroanisole; Bigl et al 2020). These detonations were performed on bare ice; nearly all generated particles were collected in discrete annuli out to 20 m surrounding the point of detonation.…”

“…LD-PSA was performed on the <2 mm fraction of samples without needles and on the <0.5 mm fraction of two samples that had sieve-removable needles by using a Horiba LA-960 (Horiba Ltd., Kyoto, Japan). The configuration of this analyzer for the processing of energetic material is described in Bigl et al (2020) and was not changed for the purposes of the analyses described below. The Horiba LA-960 was run on automatic feeder settings with the forced air pressure set to 0.03 MPa, a refractive index (RI) of 1.921 -0.002i, and sample data acquisition times of 50,000 counts (about 50 sec).…”

“…The Horiba LA-960 was run on automatic feeder settings with the forced air pressure set to 0.03 MPa, a refractive index (RI) of 1.921 -0.002i, and sample data acquisition times of 50,000 counts (about 50 sec). The process of determining the RI for these particles was consistent with the methodology described in Bigl et al (2020), and the results are described below. All samples required multiple analyses for the entirety of the sample material to pass through the analyzer during a measurement cycle.…”

“…Samples that could not be run through the Horiba LA-960 due to needleshaped particles, which clogged the instrumentation (described in Section 3.5), were analyzed using sieve-stack methods with bin sizes of 0-0.5 mm, 0.5-1 mm, and 1-2 mm, in addition to the larger bin sizes previously mentioned (Bigl et al 2020). Bigl et al (2020) outlined that LD-PSA is a more highly resolved analytical technique for energetic particle analysis; however, when that option is not feasible, sieve stack and particle-mass distribution serve as effective counterparts to LD-PSA.…”

Determination of residual low-order detonation particle characteristics from IMX-104 mortar rounds

“…To mimic factory settings of the Nilfisk GM 80 typically used on the Horiba LA-960, the suction was adjusted with the use of a variable-speed controller. The Horiba LA-960 was run on automatic feeder settings with the forced air pressure set to 0.32 MPa, a refractive index of 1.845 0.1i, and sample data acquisition times of 50,000 (Bigl et al 2020).…”