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

Researchers 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