Ceramics have many useful properties: they can be extremely durable, and hold up to very high temperatures. Unfortunately simple flaws in the material can leave the door open for catastrophic failures, making manufacturing, especially of complex shapes, challenging.

Now, a team at a company called HRL Laboratories has described a method of 3D printing ceramics. The work, which combines a number of techniques that have already been in use, can create complicated structures that are very robust and able to withstand temperatures of up to 1,700 degrees Celsius.

The foundation of the work actually dates back to the 1960s. That's when researchers developed what are called polymer-derived ceramics. These are standard polymers made of chemicals that incorporate some of the materials that are typically used to make ceramic (such as silicon and nitrogen). Once the polymer is made in the desired shape, it can be heated, which causes it to undergo chemical reactions that decompose the organic portion of the polymer. Those escape as methane or carbon dioxide, leaving behind a ceramic composed of silicon, carbon, and nitrogen.

The result is smaller than the original polymer, but it retains the original's shape. It's possible to incorporate a huge number of other elements into the polymers, allowing these polymer-derived ceramics to perform a variety of functions.

The key step used in the new work is to replace the standard polymers used to create ceramics with a chemical that polymerizes when exposed to UV light. (These can have a variety of chemistries; the authors list thiol, vinyl, acrylate, methacrylate, and epoxy groups.) This means they're able to be polymerized using a fairly standard 3D printer setup. In fact, the paper lists the model number of the version the authors bought from a different company.

These setups use a bath of the building blocks of the polymer, and expose it to a precise pattern of UV light. The polymer then forms in any regions that received a sufficiently high UV exposure.

There are two ways of using this to create a 3D object. The first is very similar to the methods of 3D printing that involve extruding a polymer: it's build up layer-by-layer, as each plane of the object is exposed sequentially. But the authors also try a method that sounds like something closer to science fiction, with a name to match: self-propagating photopolymer wave-guide technology.

SPPWGT, as we'll call it, involves ensure the polymer has the optical properties needed to channel the UV light, while the precursors do not. Thus, as each area of polymer forms, it sends on the UV light down a path that exposes more of the precursors, expanding the area that polymerizes. By using a carefully designed UV mask, it's possible to polymerize a large area much more quickly than in the layer-by-layer exposures.

The authors tried both, and they both worked. Once the polymer was set, it could be pulled out of the precursor bath and heated under argon, resulting in a ceramic. Their precursor polymer resulted in a composition that was 36 percent oxygen, 26 percent silicon, 33 percent carbon, and about four percent sulfur. The researchers tried both polymerization techniques, but found the layer-by-layer approach resulted in a series of notable "steps" between each layer. Since these could interfere with how the ceramic distributes strain, they focused on the alternate approach (SPPWGT).

HRL Laboratories, LLC

HRL Laboratories, LLC

HRL Laboratories, LLC

HRL Laboratories, LLC

HRL Laboratories, LLC

HRL Laboratories, LLC

They could use it to produce a variety of complex, 3D shapes, as shown in these images. The resulting ceramic had no surface pores or cracks, even down to the size range picked up by electron-microscopy. The resulting ceramics were extremely tough (the authors say they compared favorably to aluminum alloy honeycombs), and they could withstand temperatures of up to 1700°C with only minor surface oxidation. They may have survived higher temperatures, but the authors were unable to test that.

The authors say the resulting honeycomb structures could be perfect for cases where lightweight, heat-resistant materials are needed, like "hypersonic vehicles and jet engines."

Regardless of how they end up being used, the work represents an impressive integration of three different technologies to generate something that would be difficult, if not impossible, to produce using any one of them alone. And, given the huge variety of materials that can be incorporated into polymer-derived ceramics, it's possible that this could open the door to use cases the authors haven't foreseen.

Science, 2015. DOI: 10.1126/science.aad2688 (About DOIs).