Long‐term Coarsening and Function‐time Evolution of an Initiator Powder

Abstract

Long‐term effectiveness of high‐explosive devices necessitates maintaining a level of specific surface area of initiating powder components within specified margins. This ensures that ignition and detonation performance of the powder does not degrade significantly over time. Flow permeametry is a commonly employed surface characterization tool in this context, as embodied in the Fisher sub‐sieve surface area (FSSA). Recently we made alterations to the commercial permeametry apparatus that enables accurate in situ measurements of FSSA using only ∼100 mg samples. In this work we report on a 24‐month aging study in such modified sample holders at elevated temperatures of 40 °C and 60 °C. Through a process called time‐temperature‐superposition (TTS) the resulting isotherms are translated into a single master curve that predicts powder FSSA evolution over decades under ambient temperature conditions. We generate master curves for two different powders, i. e., pure PETN and 1 wt% added TriPEON, and show that the TriPEON‐doped powder coarsens at a rate a few times slower than the non‐doped powder. Activation barriers computed from the TTS shift factors shed some light on the coarsening mechanisms.

The Role of Pentaerythritol Tetranitrate (PETN) Aging in Determining Detonator Firing Characteristics

“…Using data from the FSSA measurements of the PETN powder, along with function time measurements, we can construct a Dinegar plot to compare particle size of various batches (aged and unaged) to function time (Figure 9). The plot shows that at consistent voltages, as surface area of the PETN decreases the function times increase, consistent with studies by Gee [25] and Dinegar [35] using unstabilized PETN. More variation in values is observed at 600 V due to the fact that we are approaching the threshold value, where function times are less reliable.…”

“…These images suggest the confined powder in the detonator assembly undergoes similar changes as the free-flowing powder and again suggest that while TriPEON does stabilize the powder, it does not stabilize as well as the polysaccharide. These results are consistent with recent work by Gee, et al that shows moderate temperature stability of triPEON-coated PETN in detonators [25]. Overall, the SEM and FSSA measurements of the loose powder correlate well with the SEM images of the powder confined in the disassembled detonators.…”

“…A number of smaller studies have been conducted analyzing the stability of specific batches of PETN powder coated with stabilizers inside detonators [24, 25]. However, there has been a lack of general consensus due to complications associated with batch‐to‐batch variability and the number of available detonators needed for statistically significant testing results.…”

Nonlinear Resonant Ultrasound Spectroscopy for Predicting Sensitivity to Initiation in Granular High Explosives

“…We conducted further measurements of the microstructure using SAXS, since elastic nonlinearity in granular materials is influenced by the microstructure, and specific surface area (SSA) has shown to be a measure of the sensitivity to initiation for loose and pressed powders [10,28]. SAXS was performed on pristine pellets and those aged at 80°C for 4, 7, and 10 weeks, as shown in Figure 8.…”

“…Powder diffraction measurements, which measure atomic to mesoscale structure, often require synchrotron sources and have not been conclusively shown to predict sensitivity to initiation. Other bulk measurements like flow permeametry only can make measurements on granular material in powder form . Linear ultrasonic techniques have been used to measure the properties of single crystals of HE , but tests on granular HE proved inconclusive.…”