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Energetic Materials

Experimental Study of Nanothermites

 1. Bockmon B. S., Pantoya M. L., Son S. F., Asay B. W., Mang J. T., Combustion Velocities and Propagation Mechanisms of Meta-stable Intermolecular Composites,” Journal of Applied Physics, 98, 2005.

2. Moore K. and Pantoya M. L., “Combustion Effects of Environmentally Altered Molybdenum Trioxide Nanocomposites,” Propellants Explosives Pyrotechnics, 2005 (in press).

3. Hunt E. M., Pantoya M. L. and Jouet R. J., “Combustion Synthesis of Metallic Foams from Nanocomposite Reactants,” Intermetallics, 2005 (in press).

4. Prentice D., Pantoya M. L., Clapsaddle B., “The Effect of Nanocomposite Synthesis on the Combustion Performance of a Ternary Thermite,” Journal of Physical Chemistry B, 2005 (in press).

5. Talantsev E. F., Pantoya M. L., Camagong C., Lahlouh B., Nicolich S. M. and Gangopadhyay S., “Ferrihydrite Gels Derived in the Fe(NO3)39H2O-C2H5OH-CH3CHCH2O Ternary System,”, Journal of Non-Crystalline Solids, vol. 351, n16-17, pp 1426-1432, 2005.

6. Hunt E. M. and Pantoya M. L., “Ignition Dynamics and Activation Energies of Metallic Thermites: From Nano- to Micron-scale Particulate Composites,” Journal of Applied Physics, Vol. 98, pp. 034909 (2005).

7. Pantoya M.L. and Granier J. J., “Combustion Behaviors of Highly Energetic Thermites: Nano versus Micron Composites,” Propellants, Explosives, Pyrotechnics, vol. 30, No. 1, pp. 53-62 (2005).

8. Plantier K. B., Pantoya M. L. and Gash A. E., “Combustion Wave Speeds of Nanocomposite Al/Fe2O3: The Effects of Fe2O3 Particle Synthesis Technique,” Combustion and Flame, vol. 140 pp. 299-309 (2005).

9. Granier J. J. and Pantoya M. L., “The Effect of Size Distribution on Burn Rate in Nanocomposite Thermites: A Probability Density Function Study,”, Combustion Theory and Modelling Vol. 8, Issue 3, pp. 555-565 (2004).

10. Granier J. J., Plantier K. B., and Pantoya M. L., “The Role of the Al2O3 Passivation Shell Surrounding Nano-Aluminum Particles in the Combustion Synthesis of NiAl,” Journal of Materials Science vol. 39 pp. 6421-6431 (2004).

11. Hunt E. M. and Pantoya M. L.,“A Laser Induced Diagnostic Technique for Velocity Measurements Using Liquid Crystal Thermography,” International Journal of Heat and Mass Transfer, Vol. 47, No. 19/20 pp. 4285-4292 (2004).

12. Hunt E. M., Granier J. J., Plantier K. B. and Pantoya M. L., “Nickel Aluminum Superalloys Created by the Self-propagating High-temperature Synthesis (SHS) of Nano-particle Reactants,” Journal of Materials Research, Vol. 19, No. 10 pp.3028-3036 (2004).

13. Hunt E., Plantier K., Pantoya M., “Nano-scale Reactants in the Self-Propagating High-Temperature Synthesis of Nickel Aluminides,” Acta Materialia Vol. 52 No. 11 pp. 3183-3191, 2004.

14. Granier J. and Pantoya M., “Laser Ignition of Nanocomposite Thermites,” Combustion and Flame, vol. 138, pp. 373-383 (2004).

15. Granier J., Mullen T. and Pantoya M., “Non-Uniform Laser Ignition in Energetic Materials,” Combustion Science and Technology 175: pp. 1929-1951, (2003).

16. Pantoya M. L. and Shaw B. D., "Molten Salt Destruction of Energetic Materials: Emission and Absorption Measurements," Journal of Energetic Materials, Volume 20(1), pp. (2002).

17. Mullen, T. A. and Pantoya, M. L., “A Spreadsheet-based analysis for two-dimensional transient laser heating of a cylindrical solid,” Heat Transfer Engineering, Vol. 26, no. 2, pp. 63-74 (2005).

18. Pantoya M., Son S., Danen W., Jorgensen B., Asay B., Busse J., and Mang J., “Characterization of Metastable Intermolecular Composites (MICs),” Chapter 16 in Defense Applications of Nanomaterials, ACS Symposium Series 891, Miziolek, A. W., Karna, S. P., Mauro, J. M., and Vaia, R. A. Editors, Copyright American Chemical Society, pp. 227-240, 2005.

Beta-Delta Phase Transformation in HMX Energetic Crystals via Virtual Melting

We theoretically predict a new phenomenon, namely that a solid-solid phase transformation (PT) with a
large transformation strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100K) below the melting temperature. We show that the energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, stresses relax and unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking
which does not affect the thermodynamics or kinetics of solid-solid transformation. Thus, virtual melting represents a new mechanism of solid-solid PT, stress relaxation and loss of coherence at a moving solid-solid interface. It also removes    the athermal interface friction and deletes the thermomechanical memory of preceding cycles of the direct-reverse transformation. It is also found that nonhydrostatic compressive internal stresses promote melting in contrast to  hydrostatic pressure. Sixteen theoretical predictions are in qualitative and quantitative agreement with experiments conducted on the PTs in the energetic crystal HMX. The virtual melting mechanism resolves numerous puzzles of               HMX polymorphism. The virtual melting mechanism allowed us to develop a physically-based thermodynamic and kinetic
model for large-scale simulation of beta-delta PT in the HMX crystals.

  1. Levitas V. I., Henson B. F., Smilowitz L. B, and Asay B. W. Solid-solid phase transformation via internal stress-induced virtual melting, significantly below the melting temperature. Application to HMX energetic crystal. J. Physical Chemistry B, 2006, Vol. 110, No. 20, 10105-10119.  pdf 
  2. Levitas V. I., Smilowitz L. B, Henson B. F., and Asay B. W. Interfacial and volumetric kinetics of the b®d phase transition in the  energetic nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine based on the virtual melting mechanism. Journal of Chemical Physics, 2006, Vol. 124, 026101.  pdf
  3. Levitas V. I., Henson B. F., Smilowitz L. B, and Asay B. W. Solid-solid phase transformation via internal stress-induced virtual melting: additional confirmations. Applied Physics Letters,  2005, Vol. 87, No. 1.   pdf
  4. Levitas V. I., Henson B. F., Smilowitz L. B, and Asay B. W. Solid-solid phase transformation via virtual melt, significantly below the melting temperature. Phys. Rev. Letters, 2004, Vol. 92, No. 23, 235702 (Selected and reproduced in Virtual J. Nanoscale Sci. & Tech., 2004, June 21) . pdf

 

New Mechanism for Fast Reaction of Nanothermites

Thermites are mixtures of metal fuel (e.g.  Al, Ti, Zr, Mg and B) and oxidizers (e.g. Fe_2O_3, MoO_3, Cu_2O, WO_3 and  CuO) or nitrdizer (e.g. teflon) which react to produce high temperatures with relatively slow oxidation reactions. Since fuel particles are covered by a thin oxide shell, oxidation is controlled by diffusion of molecules through a growing oxide shell.However, when the initial external radius R of the fuel particle is reduced to 10-60 nm (in contrast to traditional 1- 100 micrometers size), reaction rates drastically increase and flame propagation rates reach 0.9-1 km/s, in contrast to cm/s
for traditional thermites. Such reaction speeds are too fast for a diffusion controlled mechanism to be possible. In fact, a diffusion mechanism requires 10^4 –10^6 larger reaction times than observed experimentally for nano-scale particles.                                                                                                                                                                      Thus, finding the physical mechanism of material transport and reaction for nano-particulate thermites is one of the most important problems in combustion physics.

We  proposed and justified a new and unexpected mechanism for fast oxidation of Al nanoparticles covered by a thin oxide shell [1]. We argue that volume change due to melting of Al induces pressures of 0.1-4 GPa and causes spallation of the oxide shell. A subsequent unloading wave creates significant tensile pressures resulting in dispersion of atomic scale liquid Al clusters, oxidation of which is not limited by diffusion (in contrast to traditional mechanisms). Physical parameters controlling this process are determined by our analysis. Methods to promote this melt dispersion mechanism, and consequently, improve efficiency of energetic nanothermites are derived and discussed.

  1. Levitas V. I., Asay B. W., Son S. F. and Pantoya M. A mechanism for fast reaction of nanothermites
    based on dispersion of liquid metal. Applied Physics Letters, 2006, Vol. 89, No. 7, 071909.   pdf