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.