The Analysis Of Structural Characteristics And Properties Of The Shell

Mollusc shells are natural composite materials composited of a large number of calcium carbonate and a little of organic matrix. Their mechanical properties are excellent, so they have been paid attention by material devisers and investigators. This thesis summarizes that the progress of shell biomineralization and the degree to the biomimetic application. This thesis also investigates component, microstructure and crystal preferred orientation of the shell of conch Hemifusus tuba, Conus betulina linnaeus and Strombus lentiginosus Linnaeus which belong to Ggasteropod, and analysis the mechanical properties of the shell of Conus betulina linnaeus. We hope we can provide some experimental dates and theoretic foundations for the perfect of shell biomineralization theory and the design of artificial composite materials which have excellent propoties. The results of investigation are as follow:The shell of the conch Hemifusus tuba lived in Variable Zone is composited of calcite andaragonite, while the shell of Conus betulina linnaeus and Strombus lentiginosus Linnaeus lived in tropic both consist of aragonite. The conch Hemifusus tuba shell's nucleus is only composited of aragonite, tower and body whorl composed of one layer of calcite and two or more layers aragonite, and edge composed of single calcite. The calcite layer are irregular cylindrical grains, while the aragonite layers are crossed lamellar. The shell of Conus betulina linnaeus and Strombus lentiginosus Linnaeus both are composited of three aragonite layers with crossed lamellar stucture. The calcite layer and aragonite layers are multi-scale structure , and a small quantity of organic matrix distributes mainly in their grain boundary.The DSC results show that the calcite layer and aragonite layer take off hydration water in certain temperature scope. The temperature of organic matrix decomposing is different when they are in different phases, whose decomposing temperature in calcite layer is lower than in aragonite layer. With the help of hydration water and organic matrix, the transition temperature of the aragonite in the shell is lower than the natural aragonite.The XRD results indicate that there a crystal preferred orientation in each layer in three kinds of conch shell. There is a close relation between the degree to crystal preferred orientation and the shell's curvature, and the main crystal orientation become weak in the shell's curvature position.The mechanical properties of shell are anisotropic. The results of microhardness show that shell's microstructure should play important roles in their microhardness. The microhardness of calcite layer is lower than that of aragonite layer, and the hardness of their section are higher than that of their stratification plane. The results of mechanical experiments show that the loading-carrying ability of the direction vertical to stratification plane is higher than that of the direction parallel to stratification plane, and the loading-carrying ability of longitudinal section is higher than that of transverse section. The mechanical properties of the shell are higher than natural calcium carbonate due to it's particular microstructure, which is inseparable with a small quality of organic matrix in it.