Hierarchical Twin Structures in the Nacre of Red Abalone Shell
The nacre structure of red abalone (Haliotis rufescens) shell has a higher strength and fracture toughness at room temperature compared to some monolithic ceramics. The unusual mechanical properties may be attributed to the unique microarchitecture that can be described as a laminated composite of about 95% CaCO3 and 5% organic matter (a combination of proteins, chiten, and other macromolecules). It is desirable to form synthetic materials having a microarchitecture similar to the nacre through a biomimetic approach to obtain improved mechanical properties. In order to achieve this goal, it is necessary to have a better understanding of the microstructure of the nacre at different length scales. The purpose of this work was to examine the structure of nacre in more detail. It has been found that the structure is actually composed of twins which are hierarchical from the nanometer to sub-millimeter scale.