Researchers manufacture a new twist on an ancient material
Ceramics have ancient roots across the world. Now in the lab of Carolina Tallon, they are being 3D printed with the most innovative methods.
3D printers can tackle a range of unexpected materials, from metals to polymers. But ceramics have remained a puzzle. Too brittle on their own, they need to be combined with other materials in a complex mix for use in additive manufacturing.
Cutting-edge research at Virginia Tech is changing that, with a new advanced manufacturing method that 3D prints both a liquid and a solid to create novel ceramics for aerospace applications. Most surprisingly, the work of Carolina Tallon, associate professor in the Department of Materials Science and Engineering, was inspired by ancient Roman ways.
From ancient to modern
As a child growing up in Spain, Tallon saw ceramic sculptures as regularly as an American child might see fast-food restaurants. Spain’s history has included conquests by many ancient cultures that left behind an enduring history of ceramics. Whether it’s a bowl for breakfast or the depiction of an ancient Roman god, this approach to pottery and art has stood the test of time.
One method these cultures used to make ceramic pieces is called slip casting, which involves making a form into which is poured a liquid ceramic mixture. The liquid dries and hardens, the mold is taken away, and the resulting piece is heated in an oven — a process called sintering — to condense the particles and cause them to bond to one another. This transforms the material, making it denser and stronger, giving it the properties it needs for its many applications.
Of course, times have changed. But Tallon is working with Chris Williams, the L.S. Randolph Professor in the Department of Mechanical Engineering, and his team in the Virginia Tech DREAMS lab to adapt the ancient ways for the most modern machines. The partnership is also one of many within the ranks of Virginia Tech Made: The Center for Advanced Manufacturing.
The future of ceramics is in milkshakes
In the Department of Materials Science and Engineering, Tallon and her graduate student Hui-Chun (June) Yu are developing a “ceramic milkshake” for a form of slip casting made possible by a special type of 3D printer that can accommodate two different materials to form a single 3D-printed piece.
The mixture, a slurry of ceramic powders mixed into a suspension with a small amount of other chemicals, does indeed resemble a milkshake. The powders have a dark color and cause the mixture to look smooth, but you wouldn’t want to drink it. Nor can Tallon’s ceramic milkshake mixture make a finished ceramic piece by itself. But the liquid can be used in a 3D printer developed by mechanical engineering graduate researcher Ian Ho.
Printing two different materials within a single machine isn’t new technology. Williams’ team has been doing that for more than a decade. What’s new about this machine is that one of those materials is a liquid, and the other is a solid.
First, Ho's machine prints the slip cast: the thing that holds the liquid. Then Tallon’s ceramic milkshake is printed into the form after the first step finishes.
From liquid to solid
After the printing is done, the milkshake dries and the cast is removed, much like the ancient Romans might have done it. The shaped ceramic is sintered, or hit with high amounts of heat that causes the powder particles to fuse together, providing the pieces with structural properties able to resist the highest heat fluxes and temperatures.
The process allows researchers to create very small ceramics, or ceramics of unusual shapes, on the fly in a single printer. Ultimately, many of these new advanced ceramic structures will take to the skies for use in aerospace applications that require the highest heat resistance, like atmospheric reentry.
“When the Romans were working with their ceramic methods, I doubt they ever envisioned anything like this,” Tallon said. “I can only hope that this way of working with the material will be as historically significant as their work.”
