Monique McClain

Propellants, one class of what are known as energetic materials, are used to launch rockets, deploy airbags, or fire high-caliber shells and bullets. 

Companies commonly produce them by mixing together fuels, oxidizers, and other materials into a slurry that’s poured into a mold and cured. But Monique McClain, 29, an assistant professor of mechanical engineering at Purdue University, is developing ways to fine-tune the performance of propellants by producing them through a novel route: 3D printing.

The row-by-row manufacturing process promises to enable energetic materials with new shapes, more fine-grained layers, or different compositions.

This method could offer greater control over how sensitive the propellants are to detonating, how they burn over time, how energy dense they are, and other properties that affect thrust or trajectory. Similar techniques could also improve the performance of explosives, which are used for demolition, mining, and military bombs.

Manufacturing such materials is obviously dangerous. It requires carefully controlling the pressure, temperature, and conditions under which the process operates. It’s also tricky to push the thick, sticky, clay-like substances through the tiny nozzles of a 3D printer. Given these and other challenges, to date the method has largely been limited to materials with relatively low energy density, which means less explosive or propellant power.

But McClain has helped move the field forward in several ways. She was one of the first to apply an emerging technique that involves rapidly vibrating a 3D printer’s nozzle tips to extrude such viscous substances more quickly. That allowed her to print solid rocket propellants with higher energy density. McClain has also developed new techniques for assessing the characteristics of the resulting materials. 

The US Department of Defense’s Army Research Lab and several US national labs are, or will soon begin, using or evaluating some of these techniques. She can’t comment on the potential purposes of that work. But she says the methods she’s helping to develop could provide greater control over how fast rockets accelerate or how far they travel, or extend the range of other projectiles.