Picatinny aims for green with new type of primary explosive
March 21, 2014
- Researchers use sensitivity tests to understand a material's chemical components and its compatibility with other metals or energetic materials.
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PICATINNY ARSENAL, N.J. (March 21, 2014) -- One day, during a tough, live-fire training, an infantryman fires his mortar and the round is on target--an event which announces itself with flame and thunder.
When the training is done, the toxic oxide dust from the flame and smoke enters air, soil, and eventually, water, contaminating the environment.
The sources of this dust? Lead azide and lead styphnate.
These two primary sources are what have been used for years to start the chain reaction in items like mortar rounds, small caliber munitions, and rockets, triggering the more energetic secondary explosive or propellant charges.
But not only are these compounds highly sensitive, they are also toxic.
As primary explosive components in detonators and primers, lead azide and lead styphnate are sensitive to stimuli, such as impact, heat or friction.
They can be used as a neat material (a single compound) or within a formulation, a mixture of various components -- such as explosives -- oxidizers or other chemicals.
The problem is that lead azide and lead styphnate are both acute and chronic toxins that can contaminate the environment as well as affect the health of Soldiers and manufacturers who breathe in its toxic vapor.
Not only does this affect the Warfighter in combat, but it also disrupts the Warfighter's training as lead-based materials are now cataloged on the Environmental Protection Agency Toxic Chemical list and are strictly regulated under the Clean Air Act, the Clean Water Act and on the Superfund list of hazardous substances.
To resolve this issue, a Picatinny team is developing "green primary explosives" that replace lead base compounds with a more environmentally friendly chemical known as copper (II) nitrotetrazole, or DBX-1.
While their project is ongoing, the team from the Armament Research Development Engineering Center's Explosives Development Branch (including Neha Mehta and Gartung Cheng, chemical engineers, and Karl Oyler, a chemist) say that so far the results look positive and are giving DBX-1 a big, green thumbs-up.
"Once [lead azide and lead styphnate] get into the human body, they become a kind of poison that can affect the blood or target organs," Mehta said. "But, most people mistakenly think that 'green' and 'explosives' are oxymorons."
ARDEC's green primary explosives project started in 2004 in response to the Department of Defense's concerns over a 40-year-old stockpile of lead azide deteriorating at the Iowa Army Ammunition Plant in Middletown, Iowa.
At the time, no domestic manufacturers were working with lead azide due to the health concerns and high costs to produce large quantities of lead based compositions.
In 2003, the program was brought to Picatinny and given to Cheng, who was working on the M67 Fragmentation Hand Grenade Program. Chen later brought Mehta and Oyler onto the green primary explosives team.
"The specific goal of the [hand grenade] program was to improve the reliability of the C70 contained in the grenade's M213 fuze, which also contains lead azide and lead styphnate," Mehta said.
"Because it contains such large amounts of lead azide, and because of the stockpile issue, Project Manager Close Combat Systems also funded our group to test green primary explosives in replacement of the lead azide in a detonator."
Early research led the group to a metal-free, organic material known as triazine triazide, or TTA.
TTA was developed in the 1920s, but it was never adopted due to its high sensitivity.
By developing a new synthesis process, a process that induces one or more chemical reactions, the group was able to lower TTA's sensitivity.
When used as a replacement for lead azide in a large detonator, TTA fulfilled the performance requirement.
However, though TTA showed promising results in one detonator, when the team tested TTA in the smaller M55 detonator, the material didn't perform well.
For this reason, the material was dropped and the Picatinny team turned to DBX-1.
"Primary explosives themselves are by their nature extremely dangerous to handle," Mehta explained. "They can be set off from simple triggers such as dropping a half-ounce steel ball from the height of a few inches or from a static discharge. So, we have to be extremely careful in planning every activity related to handling primary explosives."
DBX-1 DROPS IN
Picatinny's green primary explosives team first heard about DBX-1 at a primary explosive workshop in Arizona, where U.S. Navy Indian Head and its contractor known as the Pacific Scientific Energetic Materials Company, briefed on how they were synthesizing a new primary explosive called DBX-1, a "drop-in" green replacement for lead azide.
"We go to conferences every year and that's where Indian Head briefed that they came up with this new material," said Mehta.
"So we said we want to test this in our Army item, the M55 detonator -- which is widely used for a lot of artillery and mortars--and when we tested it, it showed promising results: DBX-1 worked in the M55 detonator, while TTA did not."
To produce similar performance results as lead based components, though, DBX-1 must be compatible with certain criteria.
Some criteria includes being thermally stable over 150 degrees Celsius, not melting up to a point of approximately 110 degrees Celsius, possessing high detonation performance and sensitivity, long term chemical stability, does not contain toxins or heavy metals and is affordable.
DBX-1 must also undergo a variety of tests. One of these tests is a sensitivity test.
Researchers use sensitivity tests to understand a material's chemical components and its compatibility with other metals or energetic materials, as well as how to handle the material, and its susceptibility to friction, impact, and electrostatic discharge (the sudden flow of electricity between two electrically charged objects).
Another test is known as a performance test, which tests a component's characteristics, such as its instantaneous detonation, density, and whether the compound is able to perform well in small and large detonators and primers.
DBX-1 IS PUT TO THE TEST
While there are several types of performance tests, one test that the Picatinny team used to understand DBX-1 was a ball drop impact test (See figure 1).
In its ball drop impact test, DBX-1 was pressed into a small detonator (such as M55) and placed in a holder and placed onto a steel plate.
Researchers then dropped a quarter ounce steel ball onto the detonator's pin, denting the steel plate approximately 0.01 inches, a result that matched lead azide's performance.
This is the M55 detonator performance requirement according to a military specification Mil-D-14978A.
Although DBX-1 proves to be the most successful component, Mehta says there are challenges too.
The biggest challenge includes producing DBX-1 in large quantities.
This is because DBX-1 relies on a precursor material known as sodium 5-nitrotetraozole, or NaNT, but NaNT is difficult to synthesize, making the production process dangerous as it generates micro-detonations or loss of chemical reactors.
Another challenge is the flowability of DBX-1, which early reports indicated that the material did not pour into detonator cups as readily as expected.
Undaunted, the Picatinny team plans to overcome these challenges within two years and remains positive about DBX-1 as the project begins to scale up.
"The entire DoD should be able to benefit from these products," Mehta said. "The Navy has already qualified DBX-1 on the 100 gram level and soon will be incorporating it into their CAD/PAD items.
"The products will also be highly desirable to the commercial ammunitions and mining industries, which currently rely on lead-based explosives as well."
The program is the work of numerous individuals, such as Erik Hangeland with the Research, Development and Engineering Command Ordnance Environmental Program (also known as the Air-borne lead program for funding and support), technicians Akash Shah, John Marin and Kin Yee, and Branch Chief Sanjeev Singh.
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