Synchrotron XRD Study on the Nacre of Freshwater Bivalve H. cumingii Lea

Synchrotron XRD was used to study internal stress of nacre and microstructure of individual nacre tablet in the shell of freshwater bivalve H. cumingii Lea. The diffraction patterns show some biopolymers (intra―crystalline organic matrix) are occluded inside nacre tablets during biomineralization, causing that nacre powder exhibits tensile― like internal stress which is strongly anisotropic along different vectors of the reciprocal lattice. The characteristic of internal stress suggests that the intra―crystalline organic matrix is most probably arranged in the specific form. And line profile analysis which is conducted with the synchrotron XRD patterns of heated and unheated nacre powder samples, further confirms that the intra―crystalline organic matrix is adsorbed on (002) atomic planes of nacre tablets. The findings will facilitate the study on the formation mechanism and the strengthening and toughening mechanism of the nacre and provide theoretical basis for designing new organic―inorganic composite with high performances and cultivating pearl.