Nanothermite

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Nanothermite (rare Superthermit ) is the common name for metastable intermolecular mixtures ( English metastable intermolecular composites , MICs ) which by a strong exothermic reaction are distinguished by their inflammation. Nanothermites contain - analogous to ordinary thermite - an oxidizer and a reducing agent , which are finely mixed on the order of nanometers . Nanothermites are counted among the reactive materials and examined for possible use in military , explosives and pyrotechnics .

What distinguishes nanothermite from traditional thermite is the particle size of the oxidizer and reducing agent (usually iron oxide and aluminum ): They are not present as a coarse mixture (particles in the μm range), but in the form of nanoparticles , which results in new combustion properties. For example, the influence of the mass transport mechanisms on the burning rate on the nanoscopic level is not as great as on the microscopic level, which means that the reaction speed of nanothermites is significantly higher than that of the traditional thermites produced by mixing micrometer-sized components.

Types

There are many thermodynamically stable oxidizer-reducing agent combinations. However, only a handful have been researched so far. Some of them are:

Considerable attention has been paid to the combinations aluminum / molybdenum oxide, aluminum / Teflon and aluminum / copper oxide on the part of military research. Other compounds tested were based on nanoscopic RDX as well as thermoplastic elastomers . PTFE (Teflon) or other fluoropolymers can be used as the binder of the mixture. Its reaction with the aluminum adds energy to the reaction, something similar can also be observed with a magnesium / Teflon / Viton combination. Of the combinations listed here, Al / KMnO 4 has the highest reactivity , followed by the combinations Al / MoO 3 and Al / CuO with a reactivity that is about two orders of magnitude lower. Al / Fe 2 O 3 follows even more clearly .

Similar but not identical systems are nanolaminated pyrotechnic mixtures ( nano-laminated pyrotechnic Compositions ), they are as energetic Nano mixtures ( nanocomposites energetic referred). In such systems, the oxidizer and reducing agent are not necessarily in the form of tiny particles, but consist of thin layers that are arranged alternately. For example, an energetic multilayer structure can be clad with an energetic amplifier material.

By selecting the materials (almost all metals are suitable) and selecting the layer sizes, the functional properties of such a multilayer structure can be set in a targeted manner. This includes the speed of the reaction front, the ignition temperature and the energy output of the expected reaction of the layers that have not yet reacted.

production

As part of nanotechnology, the production of nanothermite is a top technology (/ high technology). In this respect, its production is subject to technical hurdles to be overcome and is only available to a very limited number of producers.
Nanoparticles can be obtained from a solution by means of spray drying , insoluble nanoparticles can be produced from suitable starting materials by means of pyrolysis . The materials can be mixed using a sol-gel process as well as conventional wet mixing and pressing.

Furthermore, the dynamic gas phase condensation ( dynamic gas-phase condensation ) a possibility nanoscale ( UFG - ultra fine grain ) to produce aluminum - a major component of most Nanothermite. This method was developed by Wayne Danen and Steve Son at Los Alamos National Laboratory . The Indian Head Division of the Naval Surface Warfare Center uses a variant of this method.

The essential requirement of every production process is the ability to produce particles in the size of a few dozen nanometers without allowing too great a variance in particle size. In 2002 it (still) required a considerable amount of effort to produce nanoscale aluminum. Commercial manufacturers were therefore hardly available.

Nanolaminated pyrotechnic compositions ( energetic nanocomposites ) of variable density can be made using the sol-gel process - a methodology traced back to Randall Simpson, Alexander Gash, and other researchers at the Lawrence Livermore National Laboratory . The supercritical extraction enables the production of highly porous and very uniform products.

inflammation

Nanothermite is easier to ignite than traditional thermite. In some cases, direct ignition can be achieved using an electronic nickel-chromium wire igniter. Other mixtures can be ignited by flames or laser pulses . The temperature in the reaction area can exceed 2700 ° C.

Applications

Metastable intermolecular mixtures (MICs) are mainly examined for possible military use (propellants, explosives, pyrotechnics). Due to its significantly higher reaction rate compared to conventional thermite, research is being carried out into nanothermite as a possible starting material for the production of new, more explosive types of bombs , including aerosol bombs . Research into nanoscopic materials with a focus on military applications began around 1990.

MICs are traded as possible successors to lead-containing (lead syphnate , lead azide ) percussion caps and electric detonators . Al / Bi 2 O 3 mixtures are suitable for this, PETN (Nitropenta) can optionally be added . Furthermore, the properties of conventional explosives can be changed by adding MICs. For example, aluminum powder is mixed with explosives to increase their energy yield, and the addition of MICs to the aluminum powder also increases the burning rate of the material.

hazards

Nanothermite is a hazardous substance because its reaction causes extremely high temperatures and once initiated, it can hardly be stopped. In addition, the composition and shape of the substance play a decisive role in nanothermite, as these have a decisive influence on the combustion properties.

A thermite reaction emits intense light in the visible and invisible spectrum (ultraviolet radiation), so that without protective measures there is a risk of blindness and burns to the skin.

See also

literature

  • A. Prakash, A. V. McCormick, M. R. Zachariah: Synthesis and Reactivity of a Super-Reactive Metastable Intermolecular Composite Formulation of Al / KMnO4 . March 30, 2005.
  • Zhang Rui, Xue Yan, Jiang Juncheng: Performance of Nanocomposite Energetic Materials Al-MoO 3 . ( DOC; 1.5 MB ( memento from February 20, 2012 in the Internet Archive ) [accessed on August 2, 2012]).
  • John J. Granier: Combustion Characteristics of Al Nanoparticles and Nanocomposite Al + MoO 3 Thermites . Ed .: Texas Tech University. May 2005.

Individual evidence

  1. ↑ Dustin T. Osborne, Michelle L. Pantoya: Effect of Al particle size on the thermal degradation of Al / teflon mixtures . In: Combustion Science and Technology . tape 179 , no. 8 , 2007, p. 1467-1480 , doi : 10.1080 / 00102200601182333 ( PDF ).
  2. ↑ a b c d e James S. Murday: The Coming Revolution: Science and Technology of Nanoscale Structures . In: AMPTIAC Quarterly . tape 6 , no. 1 , 2002 ( p2ric.org [PDF]).
  3. ^ Naval Studies Board: 2002 Assessment of the Office of Naval Research's Air and Surface Weapons Technology Program. In: The National Academies Press. National Academy of Sciences, 2002, p. 22 , accessed August 2, 2012 .
  4. ^ Anand Prakash: Reaction Kinetics and Thermodynamics of Nanothermite Propellants. March 23, 2005, accessed August 2, 2012 .
  5. ↑ a b c Patent US7951247 : Nano-laminate-based ignitors. Published on May 31, 2011 , inventor: Troy W. Barbee, Jr., Randall L. Simpson, Alexander E. Gash, Joe H. Satcher, Jr
  6. ↑ John Gartner: Military Reloads with Nanotech. In: Technology Review. MIT , January 21, 2005, accessed August 2, 2012 .
  7. ^ Todd M. Allen: Metastable Intermolecular Composites (MIC) for Small Caliber Cartridges and Cartridge Actuated Devices. (PDF, 204KB) November 2011, accessed on August 2, 2012 (English).
  8. ↑ Journal of Pyrotechnics (Ed.): Selected Pyrotechnic Publications of KL and BJ Kosanke . tape 7 ( jpyro.co.uk [accessed August 2, 2012]).
  9. ^ Chemistry Division Capabilities. (No longer available online.) In: Los Alamos National Lab: National Security Science. Los Alamos National Security, LLC, archived from the original on May 27, 2010 ; accessed on August 2, 2012 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / pearl1.lanl.gov
  10. ↑ Demitrios Stamatis, Xianjin Jiang, Ervin Beloni, Edward L. Dreizin: Aluminum Burn Rate Modifiers Based on Reactive Nanocomposite . 2008 ( ntnu.no [PDF; 262 kB ; accessed on August 2, 2012]).