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Explosives At The Microscopic Scale Produce Shocking Results

Date:
December 17, 2007
Source:
DOE/Lawrence Livermore National Laboratory
Summary:
US 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.
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Sparks are emitted from rapid chemical reactions in an energetic material. This zoomed microscopic view shows a mixture of reaction intermediates observed during a computer simulation of detonating nitromethane.
Credit: Illustration by Scott Dougherty

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.”

Other Livermore researchers include M. Riad Manaa, Laurence Fried, Kurt Glaesemann and J.D. Joannopoulos of MIT.

The work was funded by the Laboratory Directed Research and Development program.


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The above post is reprinted from materials provided by DOE/Lawrence Livermore National Laboratory. Note: Materials may be edited for content and length.


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DOE/Lawrence Livermore National Laboratory. "Explosives At The Microscopic Scale Produce Shocking Results." ScienceDaily. ScienceDaily, 17 December 2007. <www.sciencedaily.com/releases/2007/12/071211094952.htm>.
DOE/Lawrence Livermore National Laboratory. (2007, December 17). Explosives At The Microscopic Scale Produce Shocking Results. ScienceDaily. Retrieved July 3, 2015 from www.sciencedaily.com/releases/2007/12/071211094952.htm
DOE/Lawrence Livermore National Laboratory. "Explosives At The Microscopic Scale Produce Shocking Results." ScienceDaily. www.sciencedaily.com/releases/2007/12/071211094952.htm (accessed July 3, 2015).

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