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The American Ceramic Society

Innovation

3D Research Is Smooth as Glass

The first step to print compositionally graded glass optics

Published: Monday, June 12, 2017 - 12:01

Almost two years ago, Micron3DP demonstrated one of the earliest forays into 3D printing with glass. Just a few months later, MIT backed up glass’s place in the additive manufacturing realm and showed just how beautiful the possibilities were.

Although intriguing, those early demonstrations were only able to produce rather imprecise glass components with poor resolution (on the order of millimeters) because they printed in molten glass.

Although that’s good enough for glass vases, bowls, and other artistic expressions, it just doesn’t cut it for the wide range of high-tech applications of glass that require intricate and precise microstructures.

To really open up the world of additive manufacturing for glass, we need techniques that can print with better resolution, precision, and detail, which is hard to achieve with molten glass.

Now, two new papers, one published in Nature and one in Advanced Materials, describe 3D printing techniques that use silica nanoparticle inks, rather than molten glass itself, to fabricate optically clear glass components with micrometer-scale resolution, a huge leap forward for the integration of glass materials into additive manufacturing.

One of the techniques, developed by a team at Karslruhe Institute of Technology in Germany and published in Nature, prints precisely structured glass components via stereolithography with a UV-photocurable silica nanocomposite ink. About a year ago, I reported on the KIT team’s previous development of a photocurable liquid glass, which the team tweaked to develop the new printing method.

Stereolithography is a 3D printing technique that uses light to polymerize molecules layer-by-layer, hardening an ink only in areas within a given design that are exposed to the light.

By developing an ink containing glass nanopowder suspended in a photocurable polymer, the KIT team was able to use stereolithography to print a desired design at room temperature using only UV light. Then, firing the printed nanocomposite part at 1,300º C burns off the polymer and densifies the glass nanoparticles, forming a fully-glass structure, according to KIT.

“The printed fused silica glass is non-porous, with the optical transparency of commercial fused silica glass, and has a smooth surface with a roughness of a few nanometers,” according to the paper’s abstract.


Image 1: The KIT logo, 3D printed in glass. (Credit: Karslruhe Institute of Technology)


Image 2: A minuscule 3D printed glass castle. (Credit: Karslruhe Institute of Technology)


Image 3: 3D printing can even be used to fabricate microfluidic devices in glass. (Credit: Karslruhe Institute of Technology)

The KIT team’s stereolithography technique currently can print glass components with a resolution of just a few tens of micrometers, but the authors think there’s still room for improvement. According to a C&EN article, “…when the ink is used with higher resolution printing methods, the ultimate resolution should be 150–500 nm, about ten times the size of the original silica particles.”

See more about this development in a short video available on KIT’s website.

However, stereolithography isn’t the only way to 3D print glass—a separate team of scientists at Lawrence Livermore National Lab, University of Minnesota, and Oklahoma State University has also developed a technique to 3D print precise glass structures with sub-millimeter features, this time using direct ink writing.

Similar to the KIT team’s stereolithography method, the direct ink writing method also prints a silica-powder-infused liquid ink at room temperature, using a subsequent drying and sintering step “at temperatures well below the silica melting point” to form a final glass component, according to the paper’s abstract.

“This is the first step to being able to print compositionally graded glass optics,” says Rebecca Dylla-Spears, LLNL chemical engineer, project lead, and the paper’s senior author.

Direct ink writing uses a precision nozzle to deposit the ink in the desired conformation, rather than using light to harden a photocurable ink. To produce a printable ink with optimal flow—too thin and it loses its structure, too thick and it doesn’t print well—the team varied the mixture of materials to get the ink composition just right.

“For printing high-quality optics, you shouldn’t be able to see any pores and lines, they have to be transparent,” says Du Nguyen, an LLNL materials engineer. “Once we got a general formulation to work, we were able to tweak it so the material could merge during the printing process. Most other groups that have printed glass melt the glass first and cool it down later, which has the potential for residual stress and cracking. Because we print at room temperature, that’s less of an issue.”


Image 4: A new 3D printing technique could allow scientists to print glass that incorporates different refractive indices in a single flat optic, making finishing cheaper and easier. (Credit: Jason Laurea, Lawrence Livermore National Lab)


Image 5: (From left) LLNL chemical engineer and project lead Rebecca Dylla-Spears and LLNL materials engineer Du Nguyen examine a 3D printed piece of optical glass. (Credit: Jason Laurea, Lawrence Livermore National Lab)

Both 3D printing techniques—stereolithography and direct ink writing—mean big possibilities for glass, because the material has properties that make it suitable for a wide range of potential applications, including biological and medical technologies, microfluidic devices like lab-on-a-chip systems, optics, and even components for next-generation electronics.

Beyond simply replacing existing methods to manufacture glass components, scientists also are optimistic that 3D printing with glass could open new possibilities that haven’t been feasible with other techniques.

“The next-plus-one generation of computers will use light, which requires complicated processor structures; 3D technology could be used, for instance, to make small, complex structures out of a large number of very small optical components of different orientations,” says Bastian Rapp, senior author of the Nature paper.

Alternatively, the LLNL team is focusing on optical applications, including fabricating compositional gradients that haven’t been possible with alternative techniques. The team says that it may eventually be possible to print a single flat optic with different refractive indexes.

“Optical fabrication research and development is trending toward freeform optics, which are optics that can be made virtually to any complex shape,” says Tayyab Suratwala, LLNL’s program director for optics and material science and technology. “Expanding this to 3D-printed optics with compositional variation can greatly increase the capabilities of this new frontier.”

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The American Ceramic Society

Located in Westerville, OH, The American Ceramic Society (ACerS) is a non-profit professional organization for the ceramics community, with a focus on scientific research, emerging technologies, and applications in which ceramic materials are an element.

ACerS comprises more than 11,000 members from 80 countries, with membership including engineers, scientists, researchers, manufacturers, plant personnel, educators, students, and marketing and sales representatives.