The Microstructure And Properties Of Gastropoda And Cephalopoda Shells

With the development of technology,new materials which possessed high properties are need to develop to satisfy varied requirements of high technology,especially biomimetic materials have been attracted more and more attention by materials scientists.Also, biomimetic material engineering is an important means to invent new materials.Mollusc shells which are extensively studied are natural biomaterials of biomineralization that are compounded by means of the organic system's participating in it.The gastropoda abalone shell and the cephalopoda conch shell have been studied for the purpose of revealing the relationship between the two shells' structures and properties. Composition and structure of the shells are analyzed by X-ray diffraction(XRD) and scanning electron microscope(SEM);mechanical properties of the shells are analyzed by three-point bending and nanoindentation tests;physical properties of the shells are analyzed by density,thermoanalysis,and Fourier Transform Infrared Spectroscopy(FTIR) tests. Relationship between the two shells' structures and properties are discussed.It provided that some methods and conclusions for development of biomimetic materials.The experimental results showed that the abalone shell and the conch shell are both composed of calcite and aragonite.The aragonite layer of the abalone shell is like "brick and mortar",and this layer is "stack-up" in the conch shell.Some adherent substances which were considered as organic matter were observed at the fresh abalone shell's fracture by SEM.There are some results which obtained from the mechanical property tests.The strength and ductility of the fresh abalone shell are both better than the conch shell.The shell's mechanical property decreased obviously when the shell has been heated.Besides,it was enhanced by the increase of shell's growth period.In nanoindentation tests,the abalone shell's hardness was higher when test on the cross section than the plane section.It showed that with the heating-up temperature,both the density of the abalone shell and conch shell decreased gradually.At the same temperature,abalone shell's density was higher than the conch shell's.It can be concluded that the abalone shell's content of organic matter is higher than the conch shell's.From the heating experiments,it is shown that organic matter is extremely important for shell's macro-mechanical properties despite of little content.The thermal analysis tests indicated that the transformation temperature of the powder which was taken from the abalone shell's nacre is 410℃.The weight loss rate of the powder was 5% when the temperature was approaching 500℃.It is considered that such a loss is due to the decrease of organic matter.When the temperature was more than 500℃,the shell's weight decreased obviously,which was the result of calcium carbonate decomposition.