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Research and Development of High-performance Explosives
Published on: February 20, 2016
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Shock Pressure Dependence of Hot Spots in a Model Plastic-Bonded Explosive
Belinda P Johnson1, Xuan Zhou1, Dana D Dlott1
1School of Chemical Sciences and Fredrick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
The Journal of Physical Chemistry. A
|January 4, 2022
Summary
Researchers studied hot spots in cyclotetramethylene-tetranitramine (HMX) explosives under shock pressure. They found distinct pressure thresholds for hot spot formation and rapid deflagration, with temperatures exceeding 2000 K within 25 ns.
Area of Science:
- Materials Science
- Chemical Engineering
- Physical Chemistry
Background:
- Shock initiation in plastic-bonded explosives (PBX) is driven by localized energetic reactions known as 'hot spots'.
- These hot spots form where the PBX microstructure concentrates shock wave energy.
- A model system of HMX single crystals in a polyurethane binder was previously developed.
Purpose of the Study:
- To investigate the influence of input shock pressure on hot spot generation in a model PBX system.
- To determine the shock pressure thresholds for hot spot formation and subsequent explosive events.
- To characterize the temperature and timescale of hot spot development.
Main Methods:
- Utilized micrometer-resolved high-speed imaging and nanosecond-resolved optical pyrometry.
- Shocked approximately 100 HMX single crystals (HMX-SC) with pressures ranging from 12-26 GPa.
- Observed hot spot formation and thermal evolution using advanced optical diagnostics.
Main Results:
- Identified two distinct shock pressure thresholds for hot spot generation: 15 GPa for single hot spots and 23 GPa for rapid deflagration.
- Observed hot spots reaching temperatures over 2000 K within 25 ns after shock passage.
- Measured initial hot spot temperatures around 3800 K, settling to 3400 K, with an estimated flame front velocity of 550 m/s.
Conclusions:
- Shock pressure significantly influences hot spot dynamics and the initiation of explosive reactions in HMX.
- The rapid thermal explosion of nascent hot spots is a critical step in shock initiation.
- Interfacial strain energy release likely contributes to the high initial temperatures of HMX hot spots.
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