Studies On The Nanostructure Of Nacre From Haliotis Rufescens, Pinctada Maxima And Hyriopsis Cumingii

Firstly, the nanostructure of nacre from Haliotis rufescens was studies with the synchrotron X-ray powder diffraction analysis and SEM observation. The synchrotron diffraction analysis shows that an intra-crystalline organic matrix exists inside nacre tablets. And, it is confirmed to be adsorbed on the (002) atomic plane in an isolated form with SEM observation combined with line profile analysis of synchrotron diffraction profiles. It is worth to point out that the line profile analysis also suggests that some atomic groups of the intra-crystalline organic matrix are most probably connected with the (012) atomic plane. Then, SEM was used to observe the polishing-induced damage morphologies on nacre surfaces of Pinctada maxima. The results show that the polishing-induced stress by 1.5μm diamond paste can be used to reveal the nanostructure of nacre tablets. More importantly, the damage morphologies, caused by 1.5μm diamond paste, further verify the above-mentioned conclusions and give the arrangement of the intra-crystalline organic matrix, that is, it is randomly adsorbed on the (002) atomic plane in an isolated and ribbon-like form and most probably, its elongated and short direction may be parallel to the a and b axis of nacre tablet, respectively. After that, the polishing-induced stress by 1.5μm diamond paste was used to reveal the nanostructures of nacre from Haliotis rufescens and freshwater Hyriopsis cumingii. The findings suggest the above-mentioned conclusions are a widespread phenomenon for nacre and confirm previous speculation for the nanostructure of nacre from freshwater Hyriopsis cumingii, which is based on the TEM results. Interestingly, it is the first time to find that a few tablets with (012) atomic plane parallel to nacre surface exist in the nacre of Haliotis rufescens and freshwater Hyriopsis cumingii.Finally, we briefly discuss the formation mechanism and the strengthening and toughening mechanism of nacre based on the above-mentioned findings. During the formation of nacre, nucleation of aragonite mostly happens on the (002) atomic plane but a few most probably on the (012) atomic plane. It provides a new understanding for the formation of nacre. For revealing the strengthening and toughening mechanism in nano-scale, the damage morphologies under different stress state were investigated with SEM technique. SEM observation shows that nacre tablets exhibit different damage morphologies under different stress state. By combining this with the above-mentioned nanostructure, we believe that the intra-crystalline organic matrix and its interfaces with aragonite have very strong binding force. This characteristic of the nanostructure make nacre more isotropic and can improve the mechanical performance of nacre tablets.