R&D 2002: Nano Ceramics
General Electric’s nanotechnology program breaks the mold with research to toughen ceramics based on the microstructure of seashells.
Why does a ceramic coffee cup break much more easily than a seashell? That might seem like a question to ponder during a long, lazy afternoon at the beach. But General Electric, a company known in recent years for aiming its bottom line research at specific business issues, is looking for the answer and using a rather unusual strategy: it is reverse-engineering seashells. Researchers in the company’s 25-person nanotechnology group want to understand what nature has done right, as well as how nature’s approach might someday be used to build better ceramic materials for jet engines and power turbines.
Unlike typical GE research projects, the seashell effort has no specific product goals-and no time line. Indeed, say company insiders, this is exactly the type of project that just two years ago the company would have rejected as being far too speculative. But the 110-year-old corporation that gave the world better light bulbs is renewing its push to find disruptive technologies. And that has led to its work on seashells, along with many other similarly high-risk research projects that-if they ever pay off-could take up to 10 years to yield results. “This is a very new time line and level of risk for GE,” says Margaret Blohm, who heads the nanotech group.
But even though the seashell research falls into the high-risk category, it is solidly grounded in the growing discipline of nanoscience. Seashells, it turns out, have some surprising qualities, and they have been attracting the attention of researchers for more than a decade. “They’re extraordinarily tough,” says Case Western Reserve University materials science professor Arthur Heuer, who attributes their crack- and shatter-resistant properties to “an exquisite microarchitecture.” Understanding the details of this nanostructure, he adds, could lead to insights into how to make ceramics that are similarly tough and shatter resistant.
An abalone shell is made chiefly of calcium carbonate, which is organized into multisided “tablets” that are closely packed in layers. A rubbery polymer glues the tablets together and serves as a cushion between the layers. The shells are unlikely to break or shatter because when a microcrack does form, it propagates along complicated, tortuous paths that, in effect, diffuse the crack. The polymer layers also absorb the damage; so while shells get the equivalent of bumps and bruises, they don’t easily break.
GE materials scientist Mohan Manoharan and his team started work on seashells in January 2002, when the company formed its nanotech group. Before the group started trying to synthesize materials based on seashell structure, however, the researchers spent months poring over academic articles, trying to understand why “the right atom is in the right place,” says Manoharan. Their study of seashell microstructure complete, the researchers began attempts to replicate nature’s results. Manoharan’s team is building computer models of shell-inspired materials, starting with models that will consist of just a few layers. The group has also begun to synthesize the model materials.
The prospects are tantalizing for General Electric, a leading maker of high tech ceramics, including coatings that protect metal parts of jet engines against extremely high temperatures. The development of sufficiently strong and shatter-resistant lightweight ceramics could lead to all-ceramic components and, therefore, far lighter and more efficient jet engines.
For Manoharan, a former academic, the work on shells is just the type of basic research that comes naturally. When he was seven years old, he recalls, he broke his foot in a cricket accident at school in India. “I sat at home and wondered how bones healed,” he says. And he asked himself why people couldn’t build materials as sophisticated as those found in nature.
Now, years later in a lab at GE’s research center, he is pondering shells, not bones. But his question remains much the same.
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