The Biggest Bang

An accidental explosion in a German physics lab has led to the identification of a superpowerful explosive. The substance, an exotic form of silicon, is said to release seven times as much energy as TNT, and explodes a million times faster.

‘This might be the strongest explosive ever discovered,’ said Dmitri Kovalev, the physicist who runs the laboratory at the Technical University of Munich.

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 a leak in their equipment allowed air into the device, causing the silicon to exploded.

‘We realised immediately that oxygen was condensing on the sample and that the oxidation was happening explosively,’ said Kovalev.

Porous silicon has a layer of hydrogen that is one atom thick covering its surface and 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 quickly through the structure.

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.

‘Most explosive molecules contain too few oxygen atoms for a complete burn,’ said Kovalev. Because the silicon is sponge-like, it has a very high surface-area-to-volume ratio and this creates a very efficient burn.

Kovalev believes that the exploding silicon can be handled safely. ‘It requires a rather special set of conditions to explode, so in normal use it is quite safe,’ he said.

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.

Scientists are currently building thrusters comprising a silicon chip with an array of holes, which can be detonated separately, packed with conventional explosives.