Scholarship applications for Wikimania 2009 are now open. Apply now!
[Help us with translations!]

Metastable intermolecular composite

From Wikipedia, the free encyclopedia

  (Redirected from Super-thermites)
Jump to: navigation, search

Metastable intermolecular composites (MIC), also called super-thermites or superthermites, are pyrotechnic compositions containing an oxidizer and a reducing agent which undergoes a very powerful exothermic reaction when heated to a critical temperature. They are variants of thermite compositions. MICs are a type of reactive materials investigated for military use.

What separates MICs from traditional thermites is that the oxidizer and a reducing agent, normally iron oxide and aluminum are not a fine powder, but rather nanoparticles. This dramatically increases the reactivity relative to micrometre-sized powder thermite. As the mass transport mechanisms that slow down the burning rates of traditional thermites are not so important at these scales, the reactions become kinetically controlled and much faster.

There are many possible thermodynamically stable fuel-oxidizer combinations. However, only a handful have been investigated. Some of them are:

Other compositions tested were based on nanosized RDX and with thermoplastic elastomers.

PTFE or other fluoropolymer can be used as a binder for the composition. Its reaction with the aluminium, similar to magnesium/teflon/viton thermite, adds energy to the reaction. [1]

Of the listed compositions, the Al-KMnO4 one shows the highest pressurization rates, followed by orders of magnitude slower Al-MoO3 and Al-CuO, followed by yet slower Al-Fe2O3. [2]

The nanoparticles can be prepared by spray drying from a solution, or in case of insoluble oxides, spray pyrolysis of solutions of suitable precursors. The composite materials can be prepared by sol-gel techniques or by conventional wet mixing and pressing.

The nanoscale composites are easier to ignite than traditional thermites. A nichrome bridgewire can be used in some cases. Other means of ignition can include flame or laser pulse.

MICs are investigated as possible replacement for lead (e.g. lead styphnate, lead azide) containing percussion caps and electric matches. Compositions based on Al-Bi2O3 tend to be used. PETN may be optionally added. [3][4]

MICs can be also added to high explosives to modify their properties. [5] Aluminium is typically added to explosives to increase their energy yield. Addition of small amount of MIC to aluminium powder increases overall combustion rate, acting as a burn rate modifier. [6]

Similar but not identical systems are nano-laminated pyrotechnic compositions. The fuel and oxidizer is not mixed as small particles, but deposited as alternating thin layers. [7]

[edit] External links

Personal tools