Picatinny Arsenal engineers created a glass formed amorphous explosive pellet, on right, that mimics the shape of a dime. This dime is an example of how Picatinny engineers can heat an amorphous explosive beyond its glass transition point and form complex shapes.

At molecular level, Picatinny Arsenal seeks to develop versatile, transparent explosives

A research team at Picatinny Arsenal is working to produce “amorphous explosives” with nanotechnology to alter current military explosives as a way to create new, transparent explosives.

This amorphous technology could lead to new types of fuzing and explosive applications. Moreover, the team’s approach could potentially apply to other types of weapons and create new products, such as clear, reactive armor, self-destructible optics, and invisible mines. Such advances may eventually provide the future warfighter with an advantage on the battlefield.

The project is a science and technology funded initiative. The nanotechnology team, is part of the U.S. Army Armament Research, Development and Engineering Center, or ARDEC, at Picatinny Arsenal. ARDEC provides life-cycle support for nearly 90 percent of the Army’s lethality.

While nanotechnology has been of interest to ARDEC researchers for almost 20 years, the emergence of advanced technologies like high-tech computers and microscopes has recently encouraged more research in the field. This has led to an interest in specialized subjects, such as nanomaterials and nanopowders, as well as new projects like “Amorphous Explosives.”

These projects are led by Victor Stepanov and Rajen Patel, senior engineers from ARDEC’s Energetics and Warheads Manufacturing Technology Directorate.

“If you ever seen a glassblower work, they heat the material above its glass transition point (Tg) until the glass softens. Then, the glassblower manipulates the glass, easily molding it before it cools,” Rajen Patel, said about the amorphous explosives project.

“Well, with this project, we can basically do the same thing with amorphous energetics: heat them above Tg and manipulate the structure to form complex shapes.”
Pictured is a microscopic image of amorphous explosive material. In nanotechnology, “amorphous” materials means that the object lacks long-range structural order, making the object pliable, almost indistinguishable from a liquid. Everyday examples include: glass, wax, foam, gel, and sand.

In the context of defense research, “energetics” is a short-hand term for materials such as explosives, propellants and pyrotechnics.

In nanotechnology, “amorphous” materials means that the object lacks long-range structural order, making the object pliable, almost indistinguishable from a liquid. Everyday examples of amorphous materials includes: glass, wax, foam, gel, and sand.

This differs from crystalline materials, which contain a complex structure, but generally have an ordered and defined arrangement. Diamonds, graphite, and metals are some examples of crystalline materials.

There are a number of differences between the two types of materials, including shape and cleavage properties (how they break when put under stress.) But, one major difference between them is their melting points. Crystalline materials have a sharp, well-defined melting point. Amorphous materials do not.

However, if a crystalline solid is heated above its melting point and cooled quickly enough, it can become amorphous. With this in mind, the team has been testing and heating different energetic formulations, and then using rapid cooling to capture the material in its amorphous state.

This allows the team to alter a material’s structure, resulting in transparent explosives. They have also been able to eliminate defects in the material’s structure, which can potentially result in accidental initiation.

“Imagine if you have a perfect steel beam and then next to it a beam with a little crack in it. Obviously, the perfect beam is twice as strong. With the other beam, if you stress both ends, all the pressure builds up in that defect and then it breaks,” said Patel.

“It’s the same thing in energetics, if you have an energetic that experiences a shockwave and you have those defects in the structure, the pressure from the shockwave concentrates in that defect and that’s what builds hot spots and creates accidental initiation. But, with amorphous technology, we get on the nanoscale and get rid of all those defects because we’re changing the material’s structure.”

SUSTAINING AN AMORPHOUS STATE
The concept behind creating amorphous explosives was inspired by research on amorphous metals at institutions, such as Stanford University. Amorphous metals are also known as metallic glasses and can be found within everyday items, such as the heads on golf clubs or some metal knives used in the medical field.

“We realized if you could make metals amorphous, you should also be able to do the same thing with energetics,” said Patel. “Also, there has been a lot of research that covers amorphous pharmaceuticals, using techniques that directly relate to this research. In the pharmaceutical community, if you can make different drugs amorphous, you could potentially change their drug efficiency (how fast and completely they’re absorbed into the body).

Although the team is currently testing the amorphous concept within various fuzes and weapon boosters, Patel says that it could eventually be applied to weapon fills, mines, fuzes, and armor.
In addition, though the team is primarily focusing on changing a material’s optical appearance, Patel says that they could use nanotechnology and the amorphous state to alter an energetic’s sensitivity.

“Working with this technology is a lot of fun, but right now the main issue with it is sustaining the material at its amorphous state,” said Patel. “This is especially true when we talk about its military application, where we could keep something in a bunker for twenty years in a hot desert. So, that’s our current main challenge: how do we keep this material in its amorphous state?”

While some of the team’s formulations are able to maintain their amorphous state, Patel explains that these formulations still show some instability. Thus, the team continues to test different formulations that could sustain the material from aging. This includes sensitivity testing as well as optical, mechanical, and thermal characterization testing.

During thermal characterization testing, for example, different formulations are broken into small samples and tested. The sample is placed on a probe, the sample is heated, and then engineers measure the displacement of that probe.

However, Patel also explains that their ability to research amorphous explosives stems from their collaboration with other institutions, including Texas Technical University, San Diego National Labs and the U.S. Army Research Lab in Adelphi, Maryland.

“It’s not most efficient thing for us to try and address this idea all ourselves,” said Patel. “But, with National Labs, universities, and our own internal people…we can do a lot of great things.”

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The U.S. Army Armament Research, Development and Engineering Center is part of the U.S. Army Research, Development and Engineering Command, whose mission is to provide innovative research, development and engineering to produce capabilities that provide decisive overmatch to the Army against the complexities of the current and future operating environments in support of the joint warfighter and the nation.