Dr. Jan A. Puszynski Chemical and Biological Engineering Department South Dakota School of Mines

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Dr. Jan A. PuszynskiChemical and Biological
Engineering Department South Dakota School of
Mines Technology501 E. St. Joseph StreetRapid
City, SD 57701Tel [phone]Fax
605/394-1232E-mail Jan.Puszynski_at_sdsmt.eduT
2005 Annual MURI/DURINT Review Aberdeen Proving
Grounds, MD November 16-17, 2005
Kinetic Studies of Ultra-Fast Condensed- Phase
Reactions
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Research Objectives (9/1/04 8/31/05)

• Study of aluminum nanopowder reactivity in
  liquid water.
• Investigation of combustion front propagation
  characteristics under confined
• conditions.
• Measurement of pressure output of MIC systems
  under confined conditions.
• Investigation of ignition temperatures and
  reaction kinetic constants for
• different MIC systems using TGA/DSC.
• Mathematical modeling of combustion propagation
  in partially sealed cylindrical
• channels.

• Prior Research
• Investigation of Al-MoO3, Al-Fe2O3, Al-CuO,
  Al-Bi2O3 systems under unconfined
• and confined conditions.
• Dispersion and mixing of nanopowder reactants in
  organic liquids.
• Development and characterization of protective
  coatings for aluminum
• nanopowders exposed to humid air.
• Mathematical modeling of combustion front
  propagation in nanothermite
• systems.

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Mixing of energetic nanopowders in liquid water

• Advantages
• Use of environmentally benign and nonflammable
  solvent
• Excellent control of evaporation rate by
  adjusting relative humidity
• Better conditions for removing of electrostatic
  charge during
• mixing and evaporation processes
• Overall safety of the process.
• Disadvantages
• Reactivity of water with nanopowders
• Difficulties to complete drying process.

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Aluminum nanopowder reactivity in liquid
water. Selection of the hydration reaction
inhibitors.
Al nanoparticle coated with phenyltrimethoxysilane
.
T50oC

• Dibasic acids protect aluminum effectively and
  form a hydrophilic coating
• supporting dispersion of aluminum
  nanoparticles in water.
• Inhibition of the hydration reaction by use of
  succinic acid is due to a significant
• decrease of a pre-exponential factor in the
  Arrhenius equation.
• Application of succinic acid as an inhibitor
  for aluminum hydration allowed for
• preparing of Al-Bi2O3 MIC mixtures in water.

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Aluminum nanopowder reactivity in liquid water.
Effect of succinic acid concentration on
inhibition of hydration reaction.
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Aluminum nanopowder reactivity in liquid water.
Effect of temperature on hydration reaction of Al
nanopowders.
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Mixing of Aluminum and Oxide Nanopowders in Water

• Many oxide nanopowders e.g. MoO3 or WO3, have a
  relatively high solubility in
• water and should not be exposed to liquid water
  without the presence of
• protective coatings.
• Bismuth trioxide reacts very slowly with water
  and forms BiO ion.
• In the presence of aluminum, BiO is reduced to
  elemental Bi and aluminum is
• converted to aluminum hydroxide.
• Aluminum nanopowder can also react fast with
  water, if not protected.
• Addition of small amount of inhibitors, e.g.
  NH4H2PO4, reduces significantly
• the effect of those reactions over acceptable
  processing time (several hours
• to days depending on temperature)

Bi2O3 H2O ? 2BiO 2OH- BiO Al ?
Al(OH)3 Bi H Al 3H2O ? Al(OH)3
1.5H2 Al(OH)3 ? Al(OH)4- H
BiO H2PO4- ? BiPO4 H2O Al(OH)4-
H2PO4- ? BiPO4 H2O 2OH-
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Wet mixing of Bi2O3 and Al2O3 nanopowders in
hexane
SEM images
Bi2O3, SSA 1.62 m2/g, calc. average particle
size 416 nm.
Al2O3, SSA 11.4 m2/g, calc. average particle
size 132 nm.
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Wet mixing of Bi2O3 and Al2O3 nanopowders in
hexane
Choice of places for AES point analysis

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Wet mixing of Bi2O3 and Al2O3 nanopowders in
hexane
Auger electron spectroscopy at chosen points on
the sample surface (points 1 5)
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Wet mixing of Bi2O3 and Al2O3 nanopowders in
hexane
Auger electron spectroscopy at chosen points on
the sample surface (points 6 10)
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Wet mixing of Bi2O3 and Al2O3 nanopowders in
hexane
AES elemental maps of bismuth trioxide-alumina
mixture
Al
Bi

• 2D elemental maps of Bi and Al are complementary
• e-beam charging effect of the surface can be
  reduced by different technique of
• sample preparation for AES analysis (pressing
  into In foil).

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Closed-Volume Pressure Cell Experiments

• Systems investigated were Al-CuO, Al-MoO3,
  Al-Bi2O3 and Al-Fe2O3 nanopowder mixtures.
• Constant volume of powder mixture was used in
  each test.
• For comparison of different systems, all tests
  were performed in argon atmosphere to prevent a
  simultaneous reaction of aluminum with air.
• Al-CuO system was investigated to determine the
  effect of initial pressure of both air and argon
  separately on the peak pressure of the reaction
  and ignition delay.

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Closed-Volume Pressure Cell Setup
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Dynamic Pressure Responses During Ignition of
Different Nanothermite Systems
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Pressure Cell Results

• Peak pressures of 52 psig for Al-CuO, 67 psig for
  Al-MoO3, and 92 psig for the Al-Bi2O3 system were
  measured.
• Previous studies of combustion front velocity in
  open trays correlate with these results.

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Effect of Initial Pressure of Argon on Pressure
Output

• Tests were done using the Al-CuO system (30 mg
  used in each test).
• Samples were reacted at 0, 15, and 30 psig
  initial pressures.
• Intent was to determine if concentration of
  gaseous atmosphere played a significant role in
  the rate of energy release or total generated
  pressure.

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Dynamic Pressure Plot of Al-CuO System as a
Function of Initial Pressure of Argon
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Pressure Plot of Al-CuO System in Various Initial
Pressures of Air
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Force cell responses of reacting system asa
function of mass of material used
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Combustion Front Propagation in Small Diameter
Tubes

• Tubes are 1.5 inches long and 1/8 inch inside
  diameter.
• Tube is inserted into acrylic block shown left.
• Block fitted with piezoelectric pressure
  transducers.
• Setup can be configured to block either end of
  the tube shut to prevent pressure release.

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Experiments Performed

• Tests were done using the Al-Fe2O3 and Al-CuO
  systems (100 mg).
• Objective was to monitor the effect of
  confinement and pressure release on combustion
  front propagation.
• High speed video was used to record the reaction.
• This study investigated two different setups
  both tube ends open, and tube end opposite
  ignition blocked shut.

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Combustion Front PropagationBoth Tube Ends Open
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Video Stills

• Frames are taken starting at t0 in increments of
  0.0125s
• Pressure is initially released in direction of
  ignition
• Front accelerates during propagation
• Material is possibly ejected from opposite end
  prior to ignition due to pressure drop

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End Opposite Ignition Closed
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Video Stills

• Stills start at t0 and are incremented by 0.04 s
• Pressure is allowed to be released only in
  direction of ignition
• Front propagates at constant velocity
• Reaction is much slower than with both ends left
  open

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Pressure Response of Combustion Front of Al-CuO
System in Small Diameter Tubes

• Both tube ends open to atmosphere.
• Pressure transducers at distances of ½ inch and 1
  inch from point of ignition.
• Peak pressures of 908 psig and 636 psig for
  points 1 and 2 respectively.
• Total reaction time 0.2 ms compared to 100 ms
  for Al-Fe2O3 system under the same configuration.
• Results show convective, pressure driven
  combustion process.
• Future tests include monitoring reaction with
  faster high-speed camera than currently
  available.

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Determination of Reaction Kinetic Constants Using
DSC

• ASTM Standard E 474 Method used for the
  determination of Arrhenius kinetic constants of
  thermally unstable materials
• Samples are heated at varying heat rates and peak
  reaction temperatures are recorded for each
  different heat rate
• Activation energy is computed by the formula
• E -2.19Rd logß/d (1/T) where ß is the heat
  rate in C/min and T is the peak reaction
  temperature.
• Pre-exponential factor is calculated by
• Z ßEeE/RT/RT2

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Systems Investigated

• The systems initially investigated were Al-Fe2O3
  and Al-Bi2O3.
• Since oxides in both systems behave similarly at
  high temperatures, Al-MoO3 was later tested as
  MoO3 is known to sublime at elevated
  temperatures.
• The effect of particle coating on reaction
  kinetics was also determined in the Al-Bi2O3
  system with aluminum coated with an organic
  protective coating.

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DSC Plot of Reaction Peaks for the Al-Bi2O3 System
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Plot of LOG ß versus 1/T
E 221.5 kJ/mol
Z 3.8721013 min-1
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DSC Plot of Reaction Peaks for the Al-Fe2O3 System
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Plot of LOG ß versus 1/T
E 247.76 kJ/mol
Z 1.1471015 min-1
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DSC Plot of Reaction Peaks for the Al-MoO3 System
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Plot of LOG ß versus 1/T
E 207.92 kJ/mol
Z 9.471012 min-1
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Reaction Kinetics Results

• Al-MoO3 oxide sublimes E207 kJ/mol
• Ignition temperature _at_ 10oC/min heating rate is
  538oC
• Al-Bi2O3 oxide decomposes E221 kJ/mol
• Ignition temperature _at_ 10oC/min heating rate is
  553oC
• Al-Fe2O3 most stable oxide E247 kJ/mol
• Ignition temperature _at_ 10oC/min heating rate is
  565oC

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Effect of Coating on Kinetic Constants of
Nanothermite Systems

• Al-Bi2O3 system reinvestigated to determine the
  effect of particle coating on kinetic constants.
• Aluminum coated with 5 wt oleic acid.
• Calculated activation energy of 245.05 kJ/mol
  compared to 221 kJ/mol for the same mixture using
  uncoated aluminum powder.
• Peak reaction temperature at heating rate of 10
  C/min is 562.9 oC compared to 553.09 oC for the
  uncoated material.
• Pre-exponential factor for the system is 8.17
  1014 min-1, significantly higher than 3.87 1013
  min-1 for the uncoated system.

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Conclusions

• It was determined that processing of
  nanothermites in liquid water is feasible over
  the certain period of time, which is dependent on
  system temperature.
• Pressure cell experiments indicate that oxygen in
  air has a significant effect on overall energy
  output.
• Direction of pressure release have a strong
  effect on combustion front propagation velocity.
• It was demonstrated that activation energies and
  pre-exponential factors of nanothermite reactions
  can be determined using DSC technique.

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