Preparation of Desensitized Nanoenergetic Particles

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Preparation of Desensitized Nanoenergetic
Particles

• Jun Li
• University of Delaware

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Nanostructured Composite Energetic Materials

• Why?
• Nanostructured composite energetic materials
  (mixing solid oxidizers and fuels at nanoscale)
• Trade-off between power and energy density
• Less sensitivity
• Faster energy release rate
• Tailored energy properties and performance
• How?
• Conventional physical mixing incapability,
  dangerous operation
• Sol gel process or self-assembly nanoscale or
  molecular mixing and intimacy, easiness of
  synthesis

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Sol Gel Process
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Gelation and Drying

• Monolithic gel
• Polyol Energetic GAP polyol (OH functionality
  2.7, Mn5500)
• Nonenergetic polyol
• Cross-linkers isocyanate diyne and diene
• Chain extenders NC or THMNM
• Catalyst and concentration DBTDL
• Solvent Acetone or ethyl acetate
• Temperature
• High explosive CL-20
• Container
• Drying procedure
• Room temperature evaporation
• Anti-solvent precipitation and exchange
• Freeze-drying

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Precursors and Chain Extenders
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Cross-linkers
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Optimized Synthesis and Processing

• Precursor mass ratio
• Catalyst concentration
• Volume ratio of HDI to DBTDL 310
• Temperature
• 40 0C
• Solvent
• Acetone or ethyl acetate
• Synthesis step
• One step
• Drying procedure
• Modified freeze-drying Flash freeze wet gel,
  followed by low temperature vacuum evaporation

Precursor Mass ratio Max. CL-20 loading (wt) Lowest Conc. (mg/mL acetone)
GAP/HDI 90/10 85 68.78
NC/HDI 96/4 95 20.28
THMNM/HDI 37.46/62.56 90 41.6
NC/GAP/HDI 10/80.62/9.38 90 41.6
GAP/HDI/THMNM 40/39.20/20.80 90 78.23
GAP/TEGDA 85/15 90 87.88
GAP/HDI/TEGDA 87.5/5/7.5 90 87.88
NC/GAP/HDI/TEGDA 5/85.31/4.69/5 90 41.6
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Porosity of Cryrogels
NC/HDI,96/4
GAP/HDI,90/10
THMNM/HDI,37.46/62.56
NC/GAP/HDI 10/80.62/9.38
GAP/HDI/THMNM 40/39.20/20.80
GAP/TEGDA, 85/15
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SEM of Composite Energetic Materials__1
CL-20/GAP/HDI, 85/13.5/1.5
CL-20/NC/HDI, 90/9.6/0.4
CL-20/THMNM/HDI 90/3.33/6.67
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SEM of Composite Energetic Materials__2
CL-20/GAP/HDI/THMNM, 90/4/3.92/2.08
CL-20/NC/GAP/HDI, 90/1/8.06/0.94
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SEM of Composite Energetic Materials__3
CL-20/GAP/TEGDA 90/8.5/1.5
CL-20/GAP/HDI/TEGDA 90/8.75/0.5/0.75
CL-20/NC/GAP/HDI/TEGDA 90/0.5/8.53/0.47/0.5
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FT-IR Spectra
CL-20/GAP/HDI Ser
CL-20/NC/GAP/HDI Ser
CL-20/GAP/HDI/THMNM Ser

• The polymorph of CL-20 ? ? ?
• No free NCO group

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DSC
CL-20/GAP/HDI Ser
CL-20/NC/GAP/HDI Ser
CL-20/GAP/HDI/THMNM Ser
CL-20/NC/GAP/HDI/TEGDA Ser
Thermal stabilities composite energetic
materials lt CL-20, gels
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Product Distribution
CL-20/GAP/HDI Ser
CL-20/NC/GAP/HDI Ser
CL-20/GAP/THMNM/HDI Ser
CL-20/NC/GAP/HDI/TEGDA Ser
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Comparison
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Sensitivity
Flyer Plate Impact Shock Sensitivity CL-20/NC/HDI
Impact Sensitivity
Measurements made by Dr. Brian Roos at ARL on UD
samples
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Desensitizing Explanation

• Physical
• Particle size and size distribution
• Composite morphology homogenous or heterogeneous
• Polymer matrix hardness or elasticity
  sensitivity
• Thermal decomposition characteristics
• Thermal induced polymorphic phase transition
• Pure CL-20
• Effects of polymer matrix reduced phase
  transition rate
• Phase transition coupled with thermal
  decomposition for composites with low Cl-20
  loading

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Morphology of CL-20/NC/GAP/HDI Composite
65 CL-20
50 CL-20
75 CL-20
90 CL-20
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Solid Polymorphic Phase Transitions of CL-20
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Arrhenius Parameters ? Extent of Conversion
Model-free method
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Summary

• Up to 90 weight high explosive CL-20 can be
  loaded easily in energetic polymer gels with
  optimized compositions and processing. High
  content of CL-20 in solution phase did not
  disturb the formation of monolithic gels.
• Energetic polymer matrices consist of micron and
  submicron pores and nanometer thickness of
  framework.
• Drying procedure has a vital effect on the
  nanostructure of composite materials.
• Achieved homogeneity of explosive particles and
  binders at nanometer and submicron scale.
• The polymorph of CL-20 is mostly ? polymorph
  after gelation and freeze-drying.
• GAP polymer and CL-20 decomposed at similar onset
  temperatures. The interaction of CL-20 with
  polymer matrix resulted in slight lowing in
  thermal stability.
• Reduced the impact sensitivities of composite
  energetic materials.
• Product distributions of flash pyrolysis of
  composite energetic materials were not sensitive
  to CL-20 contents in the range of 50-90 weight
  and gel compositions except one composite of
  CL-20/NC/GAP/HDI/TEGDA at 90 weight CL-20.
  Secondary reactions were promoted after ignition
  because of intimacy of explosives and binders.
• Model-free apparent activation energies for CL-20
  solid polymorphic phase transitions of ?? ?, ??
  ?, and ?? ?, started at around 210 kJ/mol at 5
  conversion, increased to the maxima of about 400
  kJ/mol at 40, 80, and 60 conversion
  respectively, and then decreased.
• Polymer matrices decelerated phase transition
  phase transitions coupled with thermal
  decomposition of the composites with low CL-20
  loading where thermal stability reduced.

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Acknowledgements
Dr. Thomas B. Brill Brill Group Members Dr.
Bryce C. Tappan Dr. Brian Roos Dr. David
Miksa Dr. Brian Roos at ARL for sensitivity
test ATK for CL-20 MACH I for GAP Funding
Army Research Office, subcontract of
University of Minnesota, DURINT