Super-Strong Ceramic Mimics Seashells' Tough Mother-of-Pearl Coating

By Eliza Strickland | December 10, 2008 2:18 pm

ceramicsResearchers have created a strong, light-weight ceramic inspired by the composition of seashells, and say their new material could one day replace the aluminum alloys used in aerospace engineering. A seashell may seem like a fragile thing, but the iridescent mother-of-pearl coating on the inside of many shells has surprising toughness. Natural mother-of-pearl, also known as nacre, has a brick-and-mortar structure: Layers of “bricks” made from a calcium carbonate mineral are held together by thin films of a biopolymer “mortar” such as chitin [Chemical & Engineering News].

Researchers have tried to mimic this brick-and-mortar structure for years, but copying natural laminated materials has proved difficult, despite the best efforts of many researchers, says [lead researcher] Robert Ritchie…. Those best efforts have resulted in only very thin films, not bulk specimens with real-world practicality [New Scientist]. Now, researchers have come up with an ingenious way to produce a synthetic in large chunks, and say the material is both strong and resistant to fracture.

In the journal Science [subscription required] researchers explain that they first organize aluminum oxide plates (the “bricks”) by freezing them in ice in a method called ‘ice-templating’. Aluminium oxide plates are first suspended in water, which is then carefully frozen to produce a ceramic ‘freeze-cast’ with the plates in a regular structure [Chemistry World]. Researchers then freeze-dry the assembly to make the water ice sublimate away (at low pressure and increased temperature, the ice changes directly from a solid to a gas), and insert a gluey polymer in the spaces between the plates. That polymer serves as a cushioning “mortar,” and prevents the material from being brittle like household ceramics. The polymer permits the brick-like layers to slide over one another when stressed, making the material resistant to fractures [Technology Review].

Off the tops of their heads, the researchers list a few potential applications for the substance: It could be used for car frames, strong and insulating building materials, or bulletproof vests. Ritchie is also confident that the composites will be cheap to make, as the components … are all readily available. However, it may be some time before the material finds practical applications, he notes, as new materials have to undergo rigorous testing procedures [Chemistry World]. Researchers also need to tweak their design, because the current polymer fails at high temperatures; they’re now experimenting with metallic fillers that are more heat-tolerant.

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Image: Science

  • Jake Witmer

    The solution to the heat problem seems likely to be to include some aluminum oxide “bricks” with just enough other strong metal oxide to withstand heat, or to simply use jumbled carbon nanotubes. Why would it need to be similar to nature in appearance? Functionality is all that matters. But perhaps this will be irrelevant with the advent of better spider silk generators, and eventually, single molecule graphene fabricators. (Where one carbon molecule can be several feet in length and diameter, and completely designed in shape.)

    Also, a house, car, bike, or bulletproof vest doesn’t necessarily need to withstand extreme heat, especially if it can be built immensely faster and stronger than other building materials, and have other useful qualities. My suggestion is ‘start building’ before strong nanotech makes you obsolete. Talk to “second chance body armor” -they are open minded, and intelligent about new ideas, and already have a competent operation. Plus, they are quick to move.


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