Dec 30, 2015 | By Alec

Over the past year or so, the number of military applications of 3D printing technology have skyrocketed, but virtually all have involved metal 3D printers. However, military specialists will doubtlessly also be very interested in the success of a team of scientists from the Lawrence Livermore National Laboratory (LLNL) in California. As the team explains in a new paper in Advanced Materials, they have developed a method for 3D printing reactive materials, such as thermite, that gives them far more control over the volatile substance than ever before. Perfect for applications that need powerful, immediate bursts of energy.

Example of how thermite releases energy.

Why is this so special and what does the military have to do with it? Well, reactive materials are very interesting from a chemical perspective. They’re the type of powders that cause fantastic pyrotechnic displays in high school chemistry classes, and produce a crazy amount of heat in an instant when mixed. Nowadays, there is a whole class of reactive composite materials that don’t react chemically until they’re stimulated (with an electric shock or a laser for instance), making them very useful bomb materials. Indeed, similar primitive reactive materials were extensively used in incendiary bombs during World War II.

The only problem is that this explosive release of energy is hard to control or predict, and is thus of little use in today’s precise world. And this is where this 3D printing innovation comes in. The LLNL researchers have discovered that if you create reactive material architectures (or RMAs) from scratch using the very precise direct ink writing 3D printing technique, you gain far more control over the substances than ever before. Previously, chemists had to simply experiment with the mixing parameters to gain a modicum of control.

This new innovation, which was pioneered by a team of scientists and engineers at Lawrence Livermore National Laboratory and Harvard University, is therefore an important chemical breakthrough and has already resulted in a publication in the journal Advanced Materials. As Kyle Sullivan, the paper’s lead author explains, 3D printing has enabled them to build feature sizes that suit the length scales of dynamic phenomena. “It’s allowed us to make precision geometries, with careful control over several length scales. With this spatial control, we wanted to examine how, and to what extent, this translates into controlling dynamic behavior,” he explains.

The specific 3D printing process used is direct ink writing, which involves 3D conductive electrodes and another printing process called electrophoretic deposition (EPD), and produces thin coats of thermite nanoparticles on conductive micro architectures. These RMAs allow the researchers to easily manipulate the energy release of the thermite with unprecedented precision. “The big message here is we’re showing 3D printing can be used to change the dynamic behavior of materials,” Sullivan said. “It’s very promising moving forward.”

According to Lab engineer Eric Duoss, these results cannot be realized without the help of 3D printing technology. “Traditional thermites are random mixtures of materials,” Duoss said. “EPD gives you a tool to fix the mixing scale at the nanoscale. The film thickness, micro- and macroscale geometry can then be examined to elucidate the role of architecture on reactivity.” The team experimented with several types of these microstructures to tailor the thermite’s energy release, and they believe that the exact shape greatly affects the results

According to Sullivan, these new discoveries could be revolutionary to just about every application of reactive materials, such as air bags, ejection seats and other tools that rely on quick bursts of energy. A number of hitherto unknown applications will doubtlessly also be developed, he adds. “If you look at the history of energetic materials, the scary part is that the performance is slowly plateauing,” Sullivan said. “While it’s only a matter of time for new formulations to be developed, this technique gives us an additional knob of using material architecture to tailor, and improve, the energetic materials we already have.” In short, 3D printing could pave the way for a new paradigm in reactive material-based solutions.

 

 

Posted in 3D Printing Application

 

 

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