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International Journal of Energetic Materials and Chemical Propulsion
ESCI SJR: 0.149 SNIP: 0.16 CiteScore™: 0.29

ISSN Print: 2150-766X
ISSN Online: 2150-7678

International Journal of Energetic Materials and Chemical Propulsion

DOI: 10.1615/IntJEnergeticMaterialsChemProp.v7.i1.20
pages 17-37

MECHANOCHEMICAL MECHANISM FOR FAST REACTION OF METASTABLE INTERMOLECULAR COMPOSITES BASED ON DISPERSION OF LIQUID METAL

Valery I. Levitas
Iowa State University, Departments of Mechanical Engineering, Aerospace Engineering, and Material Science and Engineering, Ames, Iowa 50011 USA
Michelle L. Pantoya
Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409 USA

ABSTRACT

A new mechanism for fast reaction of Al nanoparticles covered by a thin oxide shell during fast heating is proposed and justified theoretically and experimentally. For nanoparticles, the melting of Al occurs before oxide fracture. The volume change due to melting induces pressures of 1-2 GPa and causes dynamic spallation of the shell. The unbalanced pressure between the Al core and the exposed surface creates an unloading wave with high tensile pressures resulting in dispersion of small liquid Al clusters. These clusters fly at high velocity and their reaction is not limited by diffusion (this is the opposite of traditional mechanisms for micron particles and for nanoparticles at slow heating). A number of theoretical predictions are confirmed experimentally. Main controlling physical parameters are determined. Some methods to expand the melt-dispersion mechanism for micron particles are formulated. This mechanism resolves some basic puzzles in combustion of Al particles. Some basic parameters of the melt-dispersion mechanism (strength of the oxide shell, heating rate necessary to activate the mechanism and size of the dispersed clusters) are estimated. It is found that the melt-dispersion mechanism may induce a new mode of energy transfer and heating ahead of flame front. Molten and reacting Al clusters are dispersed at speeds that exceed the macro-scale flame velocities of the mixture. In this way, the molten Al clusters can heat the reactant mixture prior to flame propagation. An equation for the flame velocity versus Al nanoparticle geometrical parameters, thermomechanical properties, and synthesis parameters is formulated. The melt-dispersion mechanism was also found to be in agreement with experiments for 1-3 micron diameter Al particles and fluorination. Our results completely change the direction in which the Al nanoparticle synthesis progresses.

REFERENCES

  1. National Research Council (2004).

  2. Bockmon, B., Pantoya, M., Son, S., Asay, B., and Mang, J., Combustion Velocities and Propagation Mechanisms of Metastable Interstitial Composites.

  3. Plantier, K.B., Pantoya, M.L., and Gash, A.E., Combustion Wave Speeds of Nanocomposite Al/Fe2O3: The Effects of Fe2O3 Particle Synthesis Technique.

  4. Granier, J. and Pantoya, M., Laser Ignition of Nanocomposite Thermites.

  5. Levitas, V.I., Asay, B.W., Son, S.F., and Pantoya, M.L., Melt Dispersion Mechanism for Fast Reaction of Nanothermites.

  6. Levitas, V.I., Asay, B.W., Son, S.F., and Pantoya, M.L., Mechanochemical Mechanism for Fast Reaction of Metastable Intermolecular Composites Based on Dispersion of Liquid Metal.

  7. Levitas, V.I. and Glumac, N., Burn Time of Aluminum Nanoparticles: Paradoxical Effect of the Heating Rate and Melt Dispersion Mechanism.

  8. Park, K., Lee, D., Rai, A., Mukherjee, D., and Zachariah, M., Size-Resolved Kinetic Measurements of Aluminum Nanoparticle Oxidation with Single Particle Mass Spectrometry.

  9. Bazyn, T., Krier, H., and Glumac, N., Combustion of Nanoaluminum at Elevated Pressure and Temperature Behind Reflected Shock Waves.

  10. Bazyn, T., Krier, H., and Glumac, N., Evidence for the Transition from the Diffusion-Limit in Aluminum Particle Combustion.

  11. Levitas, V.I., Pantoya, M.L. and Dikici, B., Melt Dispersion versus Diffusive Oxidation Mechanism for Aluminum Nanoparticles: Critical Experiments and Controlling Parameters.

  12. Levitas, V.I., Pantoya, M.L., and Watson, K.W., Melt Dispersion Mechanism for Fast Reaction of Aluminum Particles: Extension for Micron Scale Particles and Fluorination.

  13. Pantoya, M.L., Levitas, V.I., Granier, J.J., and Henderson, J.B., The Effect of Bulk Density on the Reaction Dynamics in Nano and Micron Particulate Thermites: Alternative Reaction and Flame Propagation Mechanisms.

  14. Pantoya, M.L. and Granier, J.J., Combustion Behavior of Highly Energetic Thermites: Nano versus Micron Composites.

  15. Moore, K., Pantoya, M.L., and Son, S.F., Combustion Behaviors Resulting from Bimodal Aluminum Size Distributions in Thermites.