by Energetic materials come in many shapes and sizes, but are often in solid form and release a lot of energy by burning or exploding, depending on their shape and the conditions in which they operate.
I am a mechanical engineering professor who studies energetic materials. Making an energetic material isn’t easy, but developments in 3D printing could make customization easier, while allowing for more scientific applications.
The role of geometry
How energetic materials are made affects the shapes they come in and how they release energy over time. For example, solid cake-like rocket propellants are made when a stand mixer stirs the “batter,” made mostly of ammonium perchlorate, aluminum, and a rubber binder, before pouring it into a pan. The “cake” solidifies in the pan as it bakes in the oven.
Rocket propellants are usually cylindrical in shape, but with a rod in the middle. The rod often has a specific cross-sectional shape, such as a circle or a star. When the drive secures, the rod is removed, leaving the heart shape behind.
The shape of the core affects how the propellant burns, which can affect the thrust of the motor it is used in. Just by changing the core shape of the drive, you can speed up, slow down or maintain the speed of a motor over time.
But this traditional “cake baking” process limits the shapes you can make. You need to be able to remove the rod after the drive has solidified, so if the shape of the rod is too complicated, you could break the drive, which could cause it to burn erroneously.
Designing propellant shapes that make rockets go faster or go further is an active area of research, but engineers need new manufacturing methods to create these increasingly complex designs.
3D printing to the rescue
3D printing has revolutionized manufacturing in many ways, and researchers like me are trying to understand how it can improve the performance of energetic materials. 3D printing uses a printer to stack material layer by layer to build an object.
3D printing allows you to make custom shapes, print different types of materials in one part, and save money and materials.
However, it is very challenging to 3D print energetic materials for several reasons. Some energetic materials are very viscous, which means that it is very difficult to squeeze that mixture out of a tube with a small nozzle. Imagine squeezing clay out of a small syringe – the material is too thick to move through the small hole easily.
In addition, energetic materials can be dangerous if handled improperly. They can ignite if there is too much heat during the manufacturing process or during storage, or if they are exposed to a static electric shock.
Recent progress
Despite this, researchers have made a lot of progress in the last decade to overcome some of these challenges. For example, scientists have 3D-printed reactive inks on electronics to enable self-destruction if they fall into the wrong hands.
In theory, you could strategically 3D print these inks onto old satellites or the aging International Space Station to break up these orbital devices into tiny enough debris that burns up in the atmosphere before hitting the ground .
Many researchers are looking into 3D printing gun propellants. By modifying the shape of the gun propellants it was possible to make bullets that could fly further.
Others have tried to use 3D printing to reduce the environmental impact of gun propellants and ignitions that require harsh solvents to make. These solvents are unsafe, difficult to dispose of and can harm the environment and human health.
I showed that it is possible to 3D print solid rocket propellants with similar properties to conventionally made propellants. With that research, we now have the opportunity to explore how propellants made of multiple materials burn, which is new territory.
For example, instead of using a rod to make a cross-sectional shape in a drive, you could 3D print a highly reactive material that you could add to the center. Instead of removing that core material, you could burn it so quickly that it leaves a core shape behind. The reactive material would also add energy to the propellant. This would eliminate the need to use and remove a rod to make a central core.
While much of this research is in its infancy, companies such as X-Bow are 3D printing propellants and conducting successful flight tests with these motors.
Finally, many researchers have studied how 3D-printed explosives detonate. When the explosives are printed in a grid-shaped lattice, they react differently when their pores are filled with air or water. This process produces a safer “portable” explosive that will not react unless in a specific environment.
3D printing energetic materials is still a new field. Scientists have a long way to go before we fully understand how 3D printing affects their safety and performance. But every day, scientists like me are finding new ways to use 3D-printed energy to fulfill vital, and sometimes life-saving, purposes.
This article is republished from The Conversation, a non-profit, independent news organization that brings you facts and analysis to help you make sense of our complex world.
Written by: Monique McClain, Purdue University.
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Monique McClain receives funding from the Air Force Office of Scientific Research (AFOSR), the Army Research Office (ARO), and the National Aeronautics and Space Administration (NASA).
