Abstract
Tridacna derasa shells show a crossed lamellar microstructure consisting of three hierarchical lamellar structural orders. The mineral part is intimately intergrown with 0.9 wt% organics, namely polysaccharides, glycosylated and unglycosylated proteins and lipids, identified by Fourier transform infrared spectrometry. Transmission electron microscopy shows nanometre-sized grains with irregular grain boundaries and abundant voids. Twinning is observed across all spatial scales and results in a spread of the crystal orientation angles. Electron backscatter diffraction analysis shows a strong fibre texture with the [001] axes of aragonite aligned radially to the shell surface. The aragonitic [100] and [010] axes are oriented randomly around [001]. The random orientation of anisotropic crystallographic directions in this plane reduces anisotropy of the Young's modulus and adds to the optimization of mechanical properties of bivalve shells.
Highlights
Bivalve shells are complex biocomposites consisting of calcium carbonate intimately intergrown at the nanoscale with organic2017 The Authors
We combine here electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM) analysis to identify some of the multi-scale strategies for the optimization of mechanical properties across all structural hierarchies in the shell
To characterize the organic matrix, the shell was decalcified in 6 N HCl after cutting and removing its outermost part, followed by a cleaning step that involved immersing the shell in 30% H2O2 (Merck KGaA, Darmstadt, Germany) and rinsing with Milli-Q water
Summary
Bivalve shells are complex biocomposites consisting of calcium carbonate intimately intergrown at the nanoscale with organic. 4 mm macromolecules [1,2] This composite nature creates enhanced material properties, for example high mechanical strength [3] and fracture toughness [4,5], which optimize shell stability and protective function for the organism [6]. We combine here electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM) analysis to identify some of the multi-scale strategies for the optimization of mechanical properties across all structural hierarchies in the shell
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