An accidental explosion in a German physics lab has led to the identification of a superpowerful explosive. The substance 鈥� an exotic form of silicon 鈥� releases seven times as much energy as TNT, and explodes a million times faster.
鈥淭his might be the strongest explosive ever discovered,鈥� says Dmitri Kovalev, the physicist who runs the laboratory at the Technical University of Munich in Garching.
Kovalev and his team were studying the optical properties of porous silicon, a sponge-like material. The group had cooled the silicon in a vacuum to the temperature of liquid nitrogen, when suddenly a leak in their equipment allowed air into the device. The silicon exploded.
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鈥淲e realised immediately that oxygen was condensing on the sample and that the oxidation was happening explosively,鈥� says Kovalev.
Chain reaction
Porous silicon has a layer of hydrogen just one atom thick covering its surface. This creates a barrier between oxygen atoms and the silicon atoms beneath. But when a single hydrogen bond breaks, an oxygen atom can bind to the silicon, starting a chain reaction that rips through the structure like wildfire.
The explosion is so violent because oxidising silicon releases a huge amount of energy compared with conventional explosives. And using liquid oxygen rather than gas means there are lots of oxygen atoms at the silicon surface.
鈥淢ost explosive molecules contain too few oxygen atoms for a complete burn,鈥� says Kovalev. Because the silicon is sponge-like, it has a very high surface-area-to-volume ratio and this creates a very efficient burn.
So far nobody has been hurt by exploding silicon and Kovalev believes that it can be handled safely. 鈥淚t requires a rather special set of conditions to explode, so in normal use it is quite safe,鈥� he says. His results will appear in Physical Review Letters.
Satellite thrusters
Leigh Canham is a physicist who specialises in porous silicon and has set up a company called pSiMedica in Malvern to exploit the material. He thinks that porous silicon could one day provide thrust for small satellites.
杏吧原创s are currently building thrusters comprising a silicon chip with an array of holes packed with conventional explosives (New 杏吧原创, 10 April 1999, p 38). Each hole can be detonated separately.
But 鈥渨hy use conventional explosives when the silicon itself could provide the thrust,鈥� asks Canham.
However, Peter Haskins, a theoretical chemist specialising in explosives, questions whether porous silicon will be ever be useful as an explosive: 鈥淭here鈥檚 certainly a lot of energy in there but whether it鈥檇 be practical to use at this temperature, I鈥檓 not so sure.鈥�