Explosives at the microscopic scale produce shocking results

Dec 11, 2007
Snapshots during a simulation of detonating nitromethane at three different times. At 5 picoseconds behind the detonation shock front (1 picosecond = one millionth of a millionth of one second), the shock has compressed the nitromethane molecules into a hot, dense liquid-like state. The first reactions occur around 8 picoseconds: hydrogen atoms are transferred to the oxygen atoms on the same molecule (white circles). Near the end of the simulation at 96 picoseconds, a mixture of transient and stable molecules exist including H2O, CO2, and HNC, HNCO. (Carbon=green, Hydrogen=white, Nitrogen=blue, Oxygen=red.)

U.S. troops blew up enemy bridges with explosives in World War II to slow the advance of supplies or enemy forces.

In modern times, patrollers use explosives at ski resorts to purposely create avalanches so the runs are safer when skiers arrive.

Other than creating the desired effect (a destroyed bridge or avalanche), the users didn’t exactly know the microscopic details and extreme states of matter found within a detonating high explosive.

In fact, most scientists don’t know what happens either.

But researchers from Lawrence Livermore National Laboratory and the Massachusetts Institute of Technology have created the first quantum molecular dynamics simulation of a shocked explosive near detonation conditions, to reveal what happens at the microscopic scale.

What they found is quite riveting: The explosive, nitromethane, undergoes a chemical decomposition and a transformation into a semi-metallic state for a limited distance behind the detonation front.

Nitromethane is a more energetic high explosive than TNT, although TNT has a higher velocity of detonation and shattering power against hard targets. Nitromethane is oxygen poor, but when mixed with ammonium nitrate can be extremely lethal, such as in the bombing of the Alfred P. Murrah Federal Building in Oklahoma City.

“Despite the extensive production and use of explosives for more than a century, their basic microscopic properties during detonation haven’t been unraveled,” said Evan Reed, the lead author of a paper appearing in the Dec. 9 online edition of the journal, Nature Physics. “We’ve gotten the first glimpse of the properties by performing the first quantum molecular dynamics simulation.”

In 2005 alone, 3.2 billion kilograms of explosives were sold in the United States for a wide range of applications, including mining, demolition and military applications.

Nitromethane is burned as a fuel in drag racing autos, but also can be made to detonate, a special kind of burning in which the material undergoes a much faster and far more violent type of chemical transformation. With its single nitrogen dioxide (NO2) group, it is a simple representative version of explosives with more NO2 groups.

Though it is an optically transparent, electrically insulating material, it undergoes a shocking transformation: It turns into an optically reflecting, nearly metallic state for a short time behind the detonation shock wave front.

But further behind the wave front, the material returns to being optically transparent and electrically insulating.

“This is the first observation of this behavior in a molecular dynamics simulation of a shocked material,” Reed said. “Ultimately, we may be able to create computer simulations of detonation properties of new, yet-to-be synthesized designer explosives.”

Source: Lawrence Livermore National Laboratory

Explore further: Tiny magnetic sensor deemed attractive

add to favorites email to friend print save as pdf

Related Stories

Recent advance in detonation theory

Nov 18, 2011

A detonation wave is a chemical reaction wave propagating at the velocity of a shock wave along the explosive charge. There is great demand for a detonation model that can accurately simulate the detonation process, which ...

In Brief: Nuclear explosion debris may reveal bomb's origin

Nov 09, 2010

Nuclear explosion debris may contain microscopic evidence that could help investigators determine the origin of the bomb, according to a study published this week in the journal Proceedings of the National Academy of Sciences.

Recommended for you

Tiny magnetic sensor deemed attractive

9 hours ago

Ultra-sensitive magnetic sensor technology pioneered at PML may soon be commercialized for a host of applications from detection of unexploded bombs and underground pipes to geophysical surveying and perhaps ...

Beams come knocking on the LHC's door

10 hours ago

Over the weekend, proton beams came knocking on the Large Hadron Collider's (LHC) door. Shooting from the Super Proton Synchrotron (SPS) and into the two LHC injection lines, the proton beams were stopped ...

Climate control in termite mounds

12 hours ago

When they make their way into homes, some species of termites can be destructive pests. Their fungus-harvesting relatives in Africa and Asia, however, are known for their construction prowess, collectively ...

The secret of dragonflies' flight

12 hours ago

Dragonflies can easily right themselves and maneuver tight turns while flying. Each of their four wings is controlled by separate muscles, giving them exquisite control over their flight.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.