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Kinetic Studies of Ultra-Fast Condensed- Phase Reactions

2005 Annual MURI/DURINT Review Aberdeen Proving Grounds, MD November 16-17, 2005.

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Kinetic Studies of Ultra-Fast Condensed- Phase Reactions

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  1. 2005 Annual MURI/DURINT Review Aberdeen Proving Grounds, MD November 16-17, 2005 Dr. Jan A. PuszynskiChemical and Biological Engineering Department South Dakota School of Mines & Technology501 E. St. Joseph StreetRapid City, SD 57701Tel: 605/394-1230Fax: 605/394-1232E-mail: Jan.Puszynski@sdsmt.eduT Kinetic Studies of Ultra-Fast Condensed- Phase Reactions

  2. 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.

  3. Mixing of energetic nanopowders in liquid water • Advantages: • Use ofenvironmentally 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.

  4. Aluminum nanopowder reactivity in liquid water. Selection of the hydration reaction inhibitors. + 3H2O(l) Al(OH)3(s) + 3/2 H2(g) Al Al nanoparticle coated with phenyltrimethoxysilane. T=50oC • 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.

  5. Aluminum nanopowder reactivity in liquid water. Effect of succinic acid concentration on inhibition of hydration reaction.

  6. Aluminum nanopowder reactivity in liquid water. Effect of temperature on hydration reaction of Al nanopowders.

  7. 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 slowlywith 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-

  8. 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.

  9. Wet mixing of Bi2O3 and Al2O3 nanopowders in hexane Choice of places for AES point analysis

  10. Wet mixing of Bi2O3 and Al2O3 nanopowders in hexane Auger electron spectroscopy at chosen points on the sample surface (points 1 – 5)

  11. Wet mixing of Bi2O3 and Al2O3 nanopowders in hexane Auger electron spectroscopy at chosen points on the sample surface (points 6 – 10)

  12. 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).

  13. 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.

  14. Closed-Volume Pressure Cell Setup

  15. Dynamic Pressure Responses During Ignition of Different Nanothermite Systems

  16. 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.

  17. 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.

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

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

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

  21. 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. Combustion Front Propagation in Small Diameter Tubes

  22. 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.

  23. Combustion Front PropagationBoth Tube Ends Open

  24. Video Stills • Frames are taken starting at t=0 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

  25. End Opposite Ignition Closed

  26. Video Stills • Stills start at t=0 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

  27. 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.

  28. 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

  29. 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.

  30. DSC Plot of Reaction Peaks for the Al-Bi2O3 System

  31. Plot of LOG β versus 1/T E = 221.5 kJ/mol Z = 3.872*1013 min-1

  32. DSC Plot of Reaction Peaks for the Al-Fe2O3 System

  33. Plot of LOG β versus 1/T E = 247.76 kJ/mol Z = 1.147*1015 min-1

  34. DSC Plot of Reaction Peaks for the Al-MoO3 System

  35. Plot of LOG β versus 1/T E = 207.92 kJ/mol Z = 9.47*1012 min-1

  36. 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

  37. 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.

  38. 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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