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Materials

Safer Explosives Still Pack A Punch

Energetic Materials: Compounds are less sensitive, less toxic than the military explosives RDX and HMX

by Elizabeth K. Wilson
September 10, 2012 | APPEARED IN VOLUME 90, ISSUE 37

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Credit: Crystal Growth & Design
A unit cell of a cocrystal of HMX (blue) and CL-20.
09037-notw8-CL20HMXcxd.jpg
Credit: Crystal Growth & Design
A unit cell of a cocrystal of HMX (blue) and CL-20.

Three new explosives from three different labs have attractive properties such as simple syntheses and relative insensitivity, making some of them possible candidates to replace current military explosive favorites, the nitramines RDX and HMX, observers say.

The design of new energetic materials stems from the need to improve the safety and reduce the environmental impact of the manufacture and use of military explosives. “The greening of its ammunition is a high priority of our defense department,” notes Keith Butler, chief chemist at American Ordnance at the Milan Army Ammunition Plant in Tennessee.

With these needs in mind, Thomas M. Klapötke, a chemistry professor at the University of Munich, and colleagues synthesized dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50). They say TKX-50 is not only safer to handle and more thermally stable than RDX but also has a higher explosive punch (J. Mat. Chem., DOI: 10.1039/c2jm33646d).

Additionally, University of Michigan chemistry professor Adam J. Matzger and colleagues report that a crystal combination of the explosives HMX and CL-20 yields an explosive more powerful than and as safe to use as HMX alone (Cryst. Growth Des., DOI: 10.1021/cg3010882).

Finally, Jean’ne M. Shreeve, a chemistry professor at the University of Idaho, and colleagues describe a new class of high-density energetic compounds based on tris(triazolo)benzene (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201205134).

RDX (cyclotrimethylenetrinitramine) has been one of the most widely used military explosives since it was synthesized more than 100 years ago. Its cousin HMX (cyclotetramethylenetetranitramine), while a superior explosive to RDX, is more friction sensitive. CL-20, or 2,4,6,8,10,12-hexanitro-2,4,6,8,10,13-hexazaisowurtzitane, is the most unstable of all—too unstable for military use.

Although RDX and HMX are superior to early explosives such as trinitrotoluene (TNT), they are highly toxic and difficult and expensive to make.

David E. Chavez, an explosives chemist at Los Alamos National Laboratory, says all three groups’ approaches hold promise to overcome such limitations. For example, the Klapötke group’s report, which includes preliminary toxicity studies, shows that TKX-50 has “promise as a potentially environmentally friendly energetic material,” he says.

The properties of the Matzger group’s HMX and CL-20 cocrystals lie somewhere between those of the two individual compounds, Chavez adds. Calculations predict that the cocrystal should be more stable than CL-20 and more powerful than HMX. “The promise these cocrystallization methods show is quite high,” Chavez says.

The Shreeve group’s tris(triazolo)benzene derivatives may lead to syntheses of promising high-nitrogen-content materials, Chavez adds.

The work from the three labs demonstrates “that chemistry is at the forefront of technological advances contributing to the effectiveness of our soldiers,” Butler says.

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Comments
Alfred G. Stern (September 12, 2012 9:09 AM)
You are incorrect about CL-20. It has good thermal stablity. It is more sensitive to shock and impact initiation than RDX or HMX. It is used for specialized military applications. It's wide scale use is precluded by its cost. It is around 30 times more expensive that RDX.
Paul Braithwaite (September 13, 2012 11:07 AM)
Elizabeth,

I agree with Alfred Stern regarding CL-20. This material is currently being used in military applications.

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