The Microstructure And Properties Of Several Gastropoda Shells

In nature, many natural biomaterials with hierarchical structure and mechanical properties provide new ideas for designing the composite material and ceramic material. And studying the hierarchical structure and mechanical properties is the most basic premise for producing biomaterial. The mollusk shell, as a typical natural biomaterial, has attracted the attention of the researchers due to its special microstructure and excellent mechanical properties. This paper takes Hemifusus tuba conch shell from the region of Yellow Sea and Bohai Sea and several tropical conch shell of gastropoda (Horned Helme conch shell, Conus betulina linnaeus shell, Common Spider Conch shell) as the object, and studies the composition, structure and characteristics of morphology by optical microscopy (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmitted electron microscopy (TEM). The structure and characteristics of morphology of Hemifusus tuba conch shell in different growth period are observed by optical microscopy (OM). The organic protein of above several mollusc shells is extracted and analyzed and the thermal behaviour is researched in detail by differential scanning caloricity (DSC) and Fourier transform infrared spectra (FTIR). The mechanical properties of Hemifusus tuba and Horned Helme conch shell are studied by 3-point bending test, compressive test and nanoindentation, and then it simulates the mechanical properties using finite element analysis. At last two biomaterials are fabricated simulating the mollusk shell's structure and the mechanical properties of them are analyzed.1. The Hemifusus tuba conch shell of temperate sea is composed of calcite and aragonite phase, and other three tropical conch shells are all composed of single phase of aragonite of crossed-lamellar. The Hemifusus tuba conch shell has different component, and the prodissoconch is composed of single aragonite, and the spire and body loop-coil are composed of outer layer of calcite and two or more layer of aragonite, yet the shell aperture fringe consists of single layer of calcite. The calcite is irregular cylindrical grains and aragonite is crossed-lamellar structure. The calcite and aragonite layer are all multiarchitecture, and a small quality of organic matrix presents discontinuous distribution at grain boundary and in grain.2. The comparative results of 3-point bending tests, compressive tests and nanoindentation tests of conch shell in different states including fresh shell ands heated shells indicate that the micromechanical properties of the heated shells at 250℃are lower than that of fresh shells..Applying the interface models of organic protein and inorganic crystal in the shell's aragonite between former and after heating states preferably explain that the mechanical properties are not only correlative to unique microstructure, but also relate with the organic matrix and the bond between the organic matrix and inorganic mineral.3. The nanoindentation results of Hemifusus tuba conch shell indicate that the modulus and hardness of aragonite are higher than that of calcite. The mechanical properties and the microcracks propagation are related to the crystal type and crystal structure. The cracks around the indentation of calcite crystals are irregular and propagate along the interface of calcite. However the cracks around the indentation of aragonite are regular and obvious, and propagate along the second-order structure. The deformation work, hardness and modulus of fresh shells are higher than that of heated shells, and which is accorded with the 3-point bending tests results.4. The 3-point bending tests, compression, microhardness and nanoindentation tests etc several experiments are applied to test the the mechanical properties of mollusc shells. The synthetical test results indicate that there exists the better corresponding relation between nanoindentation work and bending strength, nanohardness, moduls etc. And which shows that the nanoindentation test is more reasonable to test the micro/nano mechanical properties mollusk shells of biomaterial.6. The comparison between size of aragonite fiber and mechanical properties shows that the thickness of aragonite fibre increase with the accretion of growth period of Hemifusus tuba conch shell. And the slope of 3-point bending curves increases, and the bearing capacity, hardness, modulus and nanoindentation work present obvious enhancement. And which shows that the mechanical properties of mollusk shells of biomaterial are different from the higher strength and little dimension of the traditional engineering material, but it synthetically considers the microstructure and organic matrix etc factors.