Scanning electron microscope (SEM) image of an individual nanocomposite of around 2 µm. |
A
solid explosive with an energy density equivalent to that of
nitroglycerine: this is the composite material produced by researchers
at the Laboratoire d’Analyse et d’Architecture des Systèmes (CNRS) in
Toulouse, in collaboration with the Centre Interuniversitaire de
Recherche et d’Ingénierie des Matériaux, using an innovative production
process that brings nanoparticles into contact with strands of DNA.
These strands then “assemble” the various kinds of nanoparticles used.
According to the study, the released energy and ignition temperature of
the new explosive are among the best ever described in the literature.
The explosive could thus be used as an energy source to power embedded
systems, both in space and in the environment.
Nanoparticles
of aluminium and copper oxide make up the two basic ingredients of the
composite material. Although the idea of coupling aluminium with copper
oxide to produce energy is not new (they were once used to weld railway
tracks), this is the first time that DNA strands have been used to
assemble them. So why use DNA? Two complementary DNA strands (i.e. whose
molecules are able to recognize each other) self-assemble into a double
helix and then remain firmly bound together, just as they are in every
cell of our body. The researchers made use of these ‘sticky’ properties.
They separately grafted strands of DNA onto nanoscopic beads of
aluminium and of copper oxide before mixing together the two types of
nanoparticles coated with DNA strands. As a result, the complementary
strands on each type of nanoparticle bind, turning the original
aluminium and copper oxide powder into a compact, solid material which
spontaneously ignites when heated to 410 °C (one of the lowest
spontaneous ignition temperatures hitherto described in the literature).
In
addition to its low ignition temperature, this composite also offers
the advantage of having a high energy density, similar to
nitroglycerine: for the same quantity of material, it produces
considerably more heat than aluminium and copper oxide taken separately,
where a significant part of the energy is not released. In contrast, by
using nanoparticles, with their large active surfaces, the researchers
were able to approach the maximum theoretical energy for this exothermic
chemical reaction.The high energy density of this composite makes it an
ideal fuel for nanosatellites, which weigh a handful of kilograms and
are increasingly used. Such satellites are too light to be equipped with
a conventional propulsion system once in orbit. However, a few hundred
grams of this composite would give them sufficient energy to adjust
their trajectory and orientation.
The
composite could also have a host of terrestrial applications: ignitors
for gas in internal combustion engines or for fuel in aircraft and
rocket nozzles, miniature detonators, on-site welding tools, etc. Once
its heat is turned into electrical energy, the composite could also be
used as a back-up source for microsystems (such as pollution detectors
scattered through the environment).
High-Energy Al/CuO Nanocomposites Obtained by DNA-Directed Assembly
