Dr. Jan A. PuszynskiChemical and Biological Engineering Department South Dakota

School of Mines & Technology501 E. St. Joseph Street

Rapid City, SD 57701Tel: 605/394-1230Fax: 605/394-1232

E-mail: Jan.Puszynski@sdsmt.edu

T

Kinetic Studies of Ultra-Fast Condensed- Phase Reactions

2005 Annual MURI/DURINT ReviewAberdeen Proving Grounds, MD November 16-17, 2005

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.

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.

Al nanoparticle coated with phenyltrimethoxysilane.

Aluminum nanopowder reactivity in liquid water.Selection of the hydration reaction inhibitors.

• 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.

Al + 3H2O(l) Al(OH)3(s) + 3/2 H2(g)

T=50oC

0 5 10 15 20 25 30 35 400.0

0.2

0.4

0.6

0.8

1.0

ihgfedcba

extent of reaction

time [hr]

0.0 0.5 1.0 1.5 2.0 2.50

5

10

15

20

25

30

35

40

45

50

55

i

g,h

fe

dc

ba

using extent ofreaction = 0.01

from the slope ofreaction curve

reaction induction time [hr]

concentration of succininc acid [mM]

Aluminum nanopowder reactivity in liquid water.

Effect of succinic acid concentration on inhibition of hydration reaction.

Aluminum nanopowder reactivity in liquid water.

Effect of temperature on hydration reaction of Al nanopowders.

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-

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.

Wet mixing of Bi2O3 and Al2O3 nanopowders in hexane

Choice of places for AES point analysis

s9nov112.spe: Orange powder: Bi2O3-Al2O3 EAG

2005 Nov 9 15.0 keV 0 FRR 1.2589e+005 max 3.92 min

Sur1/Area1/5 (S9D9)

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

4

4.2

4.4

4.6

4.8

5

x 105 s9nov112.spe

Kinetic Energy (eV)

c/s

Photo 110/105As received

Point 1

Point 2

Point 3

Point 4

Point 5

BiAlOC

O

charging

AlO

charging

charging

O

Al

Al

Bi

BiBiC

Wet mixing of Bi2O3 and Al2O3 nanopowders in hexaneAuger electron spectroscopy at chosen points on the sample surface

(points 1 – 5)

s9nov112.spe: Orange powder: Bi2O3-Al2O3 EAG

2005 Nov 9 15.0 keV 0 FRR 1.9353e+005 max 3.92 min

Sur1/Area1/8 (S9D9)

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

x 105 s9nov112.spe

Kinetic Energy (eV)

c/s

Point 6

Point 7

Point 8

Point 9

Point 10

BiAl

OC

Al

Al

Al

BiBi

BiBiBi

BiBi

Bi

O

O

O

AlO

C

C

CBi

Bi

Bi

charging

Photo 110/105As Received

Wet mixing of Bi2O3 and Al2O3 nanopowders in hexaneAuger electron spectroscopy at chosen points on the sample surface

(points 6 – 10)

Bi Al

Wet mixing of Bi2O3 and Al2O3 nanopowders in hexaneAES elemental maps of bismuth trioxide-alumina mixture

• 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).

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.

Closed-Volume Pressure Cell Setup

Pressure Relief Valve

Gas Tank

Vacuum Pump

Pressure Vessel Oscilloscope

Sensor Signal Conditioner

Pressure Transducer

Piezoelectric Igniter

Dynamic Pressure Responses During Ignition of Different Nanothermite Systems

20

40

60

80

100

0.01 0.02

Time [s]

Pressure [psig]

Al/MoO 3

Al/Bi 2O3

Al/CuO0

20

40

60

80

100

0.01 0.02Time [s]

Pressure [psig]

Al/MoO 3

Al/Bi 2O3

Al/CuO0

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.

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.

Dynamic Pressure Plot of Al-CuO System as a Function of Initial Pressure of Argon

Al-CuO in Argon

-20

0

20

40

60

80

100

120

0 0.002 0.004 0.006 0.008 0.01 0.012

Time (s)

Pressure (psig)

30 psig Argon 15 psig Argon 0 psig Argon

Pressure Plot of Al-CuO System in Various Initial Pressures of Air

Al-CuO in Air

-20

0

20

40

60

80

100

120

0 0.002 0.004 0.006 0.008 0.01 0.012

Time (s)

Pressure (psig)

30 psig Air 15 psig air 0 psig Air

0 2 4 6 8 10 120

50

100

150

200

250

300

350

400

Al-MoO3

Al-Bi2O3

Al-CuO

recoil force [N]

mass of the MIC [mg]0 2 4 6 8 10 12

0

50

100

150

200

250

300

350

400

Al-MoO3

Al-Bi2O3

Al-CuO

recoil force [N]

mass of the MIC [mg]

Force cell responses of reacting system asa function of mass of material used

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.

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.

Combustion Front PropagationBoth Tube Ends Open

Video Stills

Frames are taken starting at t=0 in increments of 0.0125sPressure is initially released in direction of ignitionFront accelerates during propagationMaterial is possibly ejected from opposite end prior to ignition due to pressure drop

End Opposite Ignition Closed

Video Stills

Stills start at t=0 and are incremented by 0.04 sPressure is allowed to be released only in direction of ignitionFront propagates at constant velocityReaction is much slower than with both ends left open

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

Al-CuO Pressure Response

0

100

200

300

400

500

600

700

800

900

1000

0 100 200 300 400 500 600 700 800 900 1000

Time (us)

Pressure (psig)

Pressure 1 Pressure 2

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.

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 = -2.19R[d logβ/d (1/T) where β is the heat rate in

C/min and T is the peak reaction temperature.• Pre-exponential factor is calculated by: Z = βEeE/RT/RT2

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.

DSC Plot of Reaction Peaks for the Al-Bi2O3 System

536.54°C 553.09°C570.35°C

-8

-6

-4

-2

0

2

4

Heat Flow (W/g)

400 600

Temperature (°C)

––––––– Al-Bi2O3 (5 C/min)– – – – Al-Bi2O3 (10 C/min)––––– · Al-Bi2O3 (20 C/min)

Exo Up

Plot of LOG β versus 1/T

y = -12157x + 15.717R2 = 1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.00118 0.00119 0.0012 0.00121 0.00122 0.00123 0.00124

1/T (K)

LOG Heat Rate (K/min)

E = 221.5 kJ/mol

Z = 3.872*1013 min-1

DSC Plot of Reaction Peaks for the Al-Fe2O3 System

551.41°C

565.06°C 576.11°C

-6

-4

-2

0

2

4

Heat Flow (W/g)

400 600Temperature (°C)

––––––– Al-Fe2O3 (5 C/min)– – – – Al-Fe2O3 (10 C/min)––––– · Al-Fe2O3 (15 C/min)

Exo Up

Plot of LOG β versus 1/T

y = -13598x + 17.203R2 = 0.9935

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.001175 0.00118 0.001185 0.00119 0.001195 0.0012 0.001205 0.00121 0.001215

1/T (K)

LOG Heat Rate (K/min)

E = 247.76 kJ/mol

Z = 1.147*1015 min-1

DSC Plot of Reaction Peaks for the Al-MoO3 System

538.03°C

547.31°C

555.80°C

-2

0

2

4

6

8

Heat Flow (W/g)

0 200 400 600 800

Temperature (°C)Exo Up

Plot of LOG β versus 1/T

y = -11411x + 15.075R2 = 0.9957

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.001205 0.00121 0.001215 0.00122 0.001225 0.00123 0.001235

1/T (K)

LOG Heat Rate (K/min)

E = 207.92 kJ/mol

Z = 9.47*1012 min-1

Reaction Kinetics Results

• Al-MoO3 – oxide sublimes: E=207 kJ/mol– Ignition temperature @ 10oC/min heating rate is 538oC

• Al-Bi2O3 – oxide decomposes: E=221 kJ/mol– Ignition temperature @ 10oC/min heating rate is 553oC

• Al-Fe2O3 – most stable oxide: E=247 kJ/mol– Ignition temperature @ 10oC/min heating rate is 565oC

Effect of Coating on Kinetic Constants of Nanothermite Systems

578.79°C

562.98°C

572.90°C

-2

0

2

4

Heat Flow (W/g)

400 500 600 700Temperature (°C)Exo Up

y = -13449x + 17.085R2 = 0.9972

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.00117 0.001175 0.00118 0.001185 0.00119 0.001195 0.0012

1/T (K)

LOG Heat Rate (K/min)

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.

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.