TY - JOUR
T1 - Shock Pressure Dependence of Hot Spots in a Model Plastic-Bonded Explosive
AU - Johnson, Belinda P.
AU - Zhou, Xuan
AU - Dlott, Dana D.
N1 - Publisher Copyright:
© 2022 American Chemical Society
PY - 2022/1/13
Y1 - 2022/1/13
N2 - Shock initiation of plastic-bonded explosives (PBX) begins with the formation of so-called “hot spots”, which are energetic reactions localized in regions where the PBX microstructure concentrates the input shock wave energy. We developed a model PBX system to study hot spots which consists of a single crystal of the high explosive HMX (cyclotetramethylene-tetranitramine) embedded in a transparent polyurethane binder (J. Phys Chem. A, 2020, 124, 4646–4653). In the current work we use this model system to study the influence of input shock pressure (12–26 GPa) on hot spot generation using micrometer-resolved high-speed imaging and nanosecond-resolved optical pyrometry. By shocking ∼100 HMX single crystals (HMX-SC), two distinct shock pressure thresholds were observed. The threshold for producing single hot spots in some crystals was 15 GPa. At 23 GPa, hot spot density was sufficiently high to lead to rapid deflagration of the entire HMX-SC. It takes about 25 ns after the shock passes for the hot spots to appear to our visible-light detection apparatus which has a noise floor at about 2000 K. That indicates the shock produces nascent hot spots that undergo a thermal explosion that reaches temperatures >2000 K in 25 ns. The initial hot spot temperature is roughly 3800 K which settles down to 3400 K, the adiabatic flame temperature of HMX. The higher initial temperature is attributed to release of stored interfacial strain energy produced by the shock. An initial estimate for the velocity of the flame front originating at an HMX hot spot is 550 m/s.
AB - Shock initiation of plastic-bonded explosives (PBX) begins with the formation of so-called “hot spots”, which are energetic reactions localized in regions where the PBX microstructure concentrates the input shock wave energy. We developed a model PBX system to study hot spots which consists of a single crystal of the high explosive HMX (cyclotetramethylene-tetranitramine) embedded in a transparent polyurethane binder (J. Phys Chem. A, 2020, 124, 4646–4653). In the current work we use this model system to study the influence of input shock pressure (12–26 GPa) on hot spot generation using micrometer-resolved high-speed imaging and nanosecond-resolved optical pyrometry. By shocking ∼100 HMX single crystals (HMX-SC), two distinct shock pressure thresholds were observed. The threshold for producing single hot spots in some crystals was 15 GPa. At 23 GPa, hot spot density was sufficiently high to lead to rapid deflagration of the entire HMX-SC. It takes about 25 ns after the shock passes for the hot spots to appear to our visible-light detection apparatus which has a noise floor at about 2000 K. That indicates the shock produces nascent hot spots that undergo a thermal explosion that reaches temperatures >2000 K in 25 ns. The initial hot spot temperature is roughly 3800 K which settles down to 3400 K, the adiabatic flame temperature of HMX. The higher initial temperature is attributed to release of stored interfacial strain energy produced by the shock. An initial estimate for the velocity of the flame front originating at an HMX hot spot is 550 m/s.
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U2 - 10.1021/acs.jpca.1c08323
DO - 10.1021/acs.jpca.1c08323
M3 - Article
C2 - 34982934
AN - SCOPUS:85122791515
SN - 1089-5639
VL - 126
SP - 145
EP - 154
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 1
ER -