Printing in the air

The Problem

Ceramics are used in electronics, energy, aerospace, and biomedical applications. They’re extremely temperature resistant, have good chemical stability, and have high strength.

But they break easily, making them hard to manufacture. In particular, their high melting point combined with their brittleness make them bad for 3D printing.

A new 3D printing technique called direct ink writing uses a laser to print structures in the air. It works by suspending ceramic particles in a solution of light-sensitive polymers. When a UV laser light shines on the solution, the polymers join together to form a solid, holding the print in place.

The only problem is that this doesn’t usually work with ceramics. The ceramic solution absorbs the UV laser light and prevents it from joining the polymers together.

This week’s authors solved that issue by using an infrared (IR) laser light source that isn’t absorbed by the ceramic. The IR light gets through and is then converted to UV light by nanoparticles added into the ceramic-polymer solution. This UV light then joins the polymers and solidifies the print.

The Solution

The schematic below shows this process. A liquid mix of ceramics (alumina), polymers (red and blue squiggles), and nanoparticles (UCPs) are hit with an IR laser light. The nanoparticles are called upconversion particles because they convert light from a lower energy (IR) to a higher energy (UV). The UCPs convert that IR light into UV light, which makes the polymers join together into a solid.

I know the description sounds a little technical and boring. It didn’t hit me how cool this was until I watched the video. Do yourself a favor and watch the 11-second Twitter video below.

The thickness and shape of the prints are controlled using the printing speed, nozzle size, and light intensity. The prints can extend out horizontally into thin air without any supports.

This process works with many different types of ceramics. Different ceramics have different properties that can be useful in different situations. Printing with multi types of ceramics helps take advantage of their different properties by building composite structures.

Last but not least, they print some cool shapes that would be difficult or impossible with traditional 3D printing. Namely, the “flower-shaped container” (panel d), the gazebo in (e), and the wheel in (f) would all need a ton of supports to print using other methods. All of these were printed like in the video above; straight into mid-air.

See you next week for more science,

Neil