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Reactivity of nanothermites (MICs)

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- Physical mixing and chemical synthesis of redox mixtures
- Filling of one- to three-dimensional matrices with oxides and energetic materials
- Investigation of the desensitization of thermite mixtures

Contact: Marc Comet <marc.comet@isl.eu>

Thermites are fuel—oxidizer mixtures, in which the fuel is a metal or metalloid (such as aluminum) and the oxidizer is a metal oxide whose corresponding metal is more “noble”. The principal disadvantage of classical thermites is their slow energy release, with reaction times on the order of minutes.

In nanothermites, also called superthermites or Metastable Intermolecular Compounds (MICs), both oxidizer and fuel are used in the form of nanoparticles, creating a much more intimate mixture. Because of this, the reaction velocity is increased by a factor of 100 or more, which places them in the range of deflagrating explosives. NS3E prepares nanothermites with combustion velocities from a few millimeters up to hundreds of meters per second.

Goal

The goal of this research topic is to obtain high-performance reactive compositions for ignition and initiation with a reliable and controlled operation, combustion velocity and ignition delay time. They need to have a reduced sensitivity and be compatible to regulations such as the REACH directive.

In the civil domain, the main applications are igniters for the gas-generating compositions in an air bag. In this area, nanothermites could replace the toxic substances used today.

In defense, these compositions are used as an initiator for an energetic charge (explosive or propellant).

Reduction of the sensitivity

The high friction, impact and ESD sensitivity of some nanothermites is a problem for their industrial use. We developed various methods for reducing their sensitivity, as detailed in a recent review [1].

- EOR process (coating of the oxidizer by the fuel, ISL patent).

Products of the EOR process
Products of the EOR process
Transmission Electron micrograph of tungsten trioxide (WO3) particles coated by aluminum metal.

- Separation of oxidizer and fuel by introducing an inert barrier, for example carbon nanotubes or graphene.

Separation of fuel and oxidizer in a nanothermite
Separation of fuel and oxidizer in a nanothermite
The oxidizer (red) is filled into the cavity of a carbon nanotube, the oxidizer is on the outside. © 2010 American Chemical Society.

- Mixed oxide formulations (ternary thermites) allow a fine control of the reactivity and sensitivity for a defined application.

Combustion velocity of Fe2O3/CuO/P nanothermites
Combustion velocity of Fe2O3/CuO/P nanothermites
The phosphorus content is kept constant at 20 wt%, the percentage missing from 100 wt% is Fe2O3. © 2011 Royal Society of Chemistry.

[1] B. Siegert, M. Comet, D. Spitzer, Safer energetic materials by a nanotechnological approach. Nanoscale 3, 3534-3544 (2011). DOI: 10.1039/C1NR10292C.