Jim Smay, Ph.D., OSU-Tulsa associate professor of materials science and engineering, participated in a U.S. Department of Energy research project that produced a 3-D printing technique that improves transparency of fabricated glass structures.
He joined several researchers at the Lawrence Livermore National Laboratory who developed a two-part process using direct ink writing to produce transparent glass with sub-millimeter precision, a method previously impossible through conventional manufacturing processes.
The discovery opens a pathway to capitalize on the manufacturing advantages of 3-D printing in glass, a material traditionally difficult to use in 3-D printing.
“The importance of glass as an engineering material is well-known and researchers worldwide are seeking to use 3-D printing to precisely control composition and structure for advancement of numerous optical devices, including lasers,” Smay said.
Other glass 3-D printing approaches involve extruding molten glass through a nozzle at 1800 degrees Fahrenheit. The new method uses a room temperature process followed by a high-temperature fusion step.
“The key to making our two-step process work is to engineer the flow behavior of the ink to be easily extruded through a fine gauge hypodermic needle – the nozzle – but have a spontaneous return to solid-like behavior immediately after extruding the ink,” Smay said. “We can all recognize this as the behavior of toothpaste where we don’t want to work too hard to squeeze it out of the tube, but we want it to stiffen enough so that it does not flow down into the bristles of the toothbrush.”
To achieve proper flow, researchers developed a colloidal gel ink by combining nano-sized particles with a volatile liquid. Once the ink is extruded in a programmable pattern, the gel rapidly solidifies. Next, the printed structures are dried and heated, resulting in a transparent glass structure without cracks or visible lines.
“The heating step fuses the particles together, without melting, and eliminates porosity; a process called sintering,” Smay said. “Anyone who has wondered why their ice cubes get stuck together in the freezer when the temperature was never high enough to melt them has experience with sintering. Removal of porosity is critical to making the glass transparent.”
Researchers will continue working to improve and refine the 3-D glass printing method and further explore the grading of composition while printing to enable novel optical devices.
In addition to Smay, the research team includes scientists and engineers from the University of Minnesota and the Lawrence Livermore National Laboratory. The team published the results of their research in the journal Advanced Materials on April 28.
Smay is resident faculty in the OSU School of Materials Science and Engineering, located at the Helmerich Research Center at OSU-Tulsa. To learn more about the OSU School of Materials Science and Engineering, visit the program website.