Materials Performance

DEC 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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9 MATERIALS PERFORMANCE: VOL. 57, NO. 12 DECEMBER 2018 Continued on page 10 UP FRONT Novel Process Produces Superior Graphene Prints Researchers at Virginia Tech University (Blacksburg, Virginia, USA) and Lawrence Livermore National Laboratory (LLNL) (Livermore, California, USA) have developed a novel way to make three-dimensional (3-D) prints of graphene. In the past, researchers could only print graphene in two-dimensional sheets, or basic structures. But here, engineers say they have unlocked the ability for the 3-D printing of graphene objects at a resolution an order of magnitude greater than before. Because of their strength and high thermal and electricity conductivity, 3-D printed graphene objects could be useful in industries such as batter- ies, aerospace, separa- tion, heat management, sensors, and catalysis. Graphene is a single layer of carbon atoms organized in a hexagonal lattice. When graphene sheets are neatly stacked on top of each other and formed into a 3-D shape, it becomes graphite, commonly known as the "lead" in pencils. Because graphite is simply packed-together graphene, it has subpar mechanical properties, the researchers explain. But if the graphene sheets are separated with air-filled pores, the 3-D structure can maintain its properties. This porous graphene structure is called a graphene aerogel. "Now a designer can design three-dimensional topology comprised of intercon- nected graphene sheets," says Xiaoyu "Rayne" Zheng, an assistant professor at Virginia Tech's department of mechanical engineering. "This new design and manu- facturing freedom will lead to optimization of strength, conductivity, mass transport, strength, and weight density that are not achievable in graphene aerogels." Previously, researchers could print graphene using an extrusion process, which they compare to squeezing toothpaste. But that technique could only create simple, stackable objects. "With that technique, there are very limited structures you can create because there's no support and the resolution is quite limited, so you can't get freeform factors," Zheng says. "What we did was to get these graphene layers to be architected into any shape that you want with high resolution." To create these new structures, the researchers started with graphene oxide, a precursor to graphene, crosslinking the sheets to form a porous hydrogel. Breaking the graphene oxide hydrogel with ultrasound and adding light-sensitive acrylate polymers, they then used projection micro-stereolithography to create the desired solid 3-D structure with the graphene oxide trapped in the long, rigid chains of acry- late polymer. Finally, they placed the 3-D structure in a furnace to burn off the poly- mers and fuse the object together, leaving a lightweight graphene aerogel. While other processes could print down to 100 ›m, the new technique allows researchers to print down to 10 ›m in resolution, approaching the size of actual gra- phene sheets. "We've been able to show you can make a complex, 3-D architecture of graphene while still preserving some of its intrinsic prime properties," Zheng says. For more information, visit vtnews.vt.edu. While prior graphene processes could print down to 100 m, the new 3-D technique allows researchers to print down to 10 m in resolution. Image courtesy of Virginia Tech. New Alloy Withstands Ultrahigh Temperatures, Pressure The creep test machine. Photo by Kyosuke Yoshimi, Tohoku University. Scientists at Tohoku University (Sendai, Japan) have found that a molybdenum- silicon-boron alloy reinforced with titanium carbide (TiC) can withstand constant forces in ultrahigh-temperature ranges of 1,400 to 1,600 °C. "Our experiments show that the MoSiBTiC alloy is extremely strong com- pared with cutting-edge nickel-based single crystal superalloys, which are commonly used in hot sections of heat engines such as jet engines of aircrafts and gas turbines for electric power generation," says Kyosuke Yoshimi, a professor at Tohoku's graduate engineering school and lead author of the associated research paper. Yoshimi and colleagues report several parameters that highlight the alloy's ability to withstand disruptive forces under ultra- high temperatures without deforming. They also observed the MoSiBTiC alloy's behavior when exposed to increasing forces and when cavities within it formed and grew, resulting in microcracks and final rupturing. According to the researchers, enhancing the functionality of heat engines may deter- mine how efficient they are at energy con- version. Creep behavior—or the material's

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