Tough-as-nails ceramic inspired by mother-of-pearl
By Ben Coxworth
March 25, 2014
Although you may know it simply as the shiny iridescent stuff on the inside of mollusk shells, mother-of-pearl (or nacre) is a remarkable material. It allows those shells, which otherwise consist almost entirely of brittle calcium carbonate, to stand up to the abuses of life in the sea. Now, a team led by the Laboratoire de Synthèse et Fonctionnalisation des Céramiques (CNRS) in Paris, has copied the structure of nacre to create a ceramic material that's almost 10 times stronger than conventional ceramics.
Natural nacre consists of layers of microscopic tablet-like blocks, that have wavy edges not unlike jig-saw puzzle pieces. This means that when the material is subjected to mechanical stress, any cracks that start to form in the boundary lines between the tablets have to follow a very circuitous route. As a result, all but the largest cracks simply just peter out.
Scientists at Montreal's McGill University recently created super-strong glass, by etching nacre boundary line-like cracks in glass microscope slides. The CNRS team, however, took a different approach with the ceramic.
They started with a ceramic powder, made up of microscopic alumina platelets. That powder was suspended in water, and the resulting solution was then frozen. The ice crystallization process caused the platelets to self-assemble into stacks, the boundaries between which were similar to the wavy boundaries between nacre tablets. A high-temperature process was then used to increase the density of the material, thus removing the water.
In lab tests of the resulting ceramic, it was found that cracks had great difficulty spreading through it – as is the case with real nacre.
Additionally, the scientists state that the process should work with any type of ceramic powder (not just alumina), and it should be easy to scale up to industrial production levels. Besides simply making existing types of ceramic items stronger, the technology could also allow them to stay at the same strength, but be made much smaller.
A paper on the research was recently published in the journal Nature Materials.