CaCO₃晶体的体外模拟生长过程及机理研究

【作者】 罗程；

【导师】 王小祥；

【作者基本信息】 浙江大学 ， 材料科学与工程学， 2007， 硕士

【摘要】 软体动物的贝壳珍珠质是由文石板片（CaCO₃晶体）以及少量填充在板片之间的有机质组成的一种天然的复合材料，具有复杂的形貌以及良好的力学性能、光学性能，其文石板片与有机基质交替叠层排列的微结构以及文石晶体的结晶学取向是珍珠层具有优异的力学性能的重要原因之一。在生物矿化过程中，生物体能从纳米到微米级的尺度上对文石板片的矿化过程进行精确的控制。这些特殊的性质和精确的调控能力引起了研究者极大的兴趣。由于缺乏珍珠层生物矿化过程中CaCO₃形核及生长的有效证据，至今为止还没有一种理论能完全解释矿化过程中珍珠层的形成机理。本文首先采用扫描电镜（SEM）、X射线衍射仪等研究了我国重要的淡水珠母贝——三角帆蚌（Hyriopsis cumingii Lea）中珍珠层的结构性质。三角帆蚌珍珠层为砖墙型结构，文石板片主要沿（002）晶面方向择优取向。其次，本文采用传统的气相扩散方法，在没有任何添加剂的溶液中，进行了珍珠质基底上CaCO₃晶体的体外沉积实验。实验分别研究了CaCl₂溶液浓度、沉积时间、沉积基底以及沉积温度等条件的不同对CaCO₃晶体的组成、形貌的影响。SEM、Raman及XRD等分析表明，在以新鲜的三角帆蚌贝壳珍珠层为基底的沉积实验中，可以获得完全由文石小板片组成的塔状堆垛，并能观察到天然文石板片边缘沉积的无定形颗粒逐渐转变为六角形板片的过程。而在无基底或以载波片为基底的对照实验中，仅能获得方解石斜方六面体及球状球文石晶体。本文初步探讨了CaCO₃晶体在体外沉积的形核、生长、形貌、取向等的机制，认为层片状的文石堆垛的生长过程与软体动物中天然珍珠层的矿化过程类似，并希望本实验的结果对理解软体动物贝壳中珍珠层的生长机理有所帮助。更多还原

【Abstract】 The nacre of molluscan shell, which is composed of inorganic aragonite tablets and a few percent of organic polymers filling between the tablets, is a wonderful natural composite material. It shows complex forms, and fascinating mechanical and optical properties. The extraordinarily excellent properties are resulted from the unique layered microstructure, the crystallographic orientation of aragonite tablets and the exquisite control of crystallization over several length scales in biomineralization processes. All of these inspire the research of shell nacre. However, the mechanism of nacre formation is still poorly understood because of lack of sufficient experiment evidences on the nucleation and growth of CaCO₃ in biomineralization process of nacre.In the present study, we conducted SEM and X-ray diffraction experiments to study the microstructure of nacre of Hyriopsis cumingii Lea. The results showed that the nacre is built from a "Brick-Wall" of plate-like aragonite crystals and the aragonite tablets are aligned along （002） direction. Secondly, we conducted an in vitro experiment to simulate the growth of aragonite on nacre surface via the vapor diffusion method in the absence of any other additional additives. By varying the time, substrates, temperature of deposition and CaCl₂ solution concentration, the aragonitic crystals formed on the nacre surface were investigated with SEM, Raman and XRD. The results showed that tower-like stacks of layered aragonite tablets were deposited along the edge of the natural aragonite tablets of nacre, and these layered aragonite tablets obtained after deposition for 24h were transformed from amorphous particles formed at the early stage. In control experiment, the deposit on glass slices is composed of calcite and vaterite. The mechanisms of nucleation, growth, morphology and orientation of the CaCO₃ crystals deposited in vitro on nacre surface were discussed in this paper. Because the environment of the calcium carbonate formation in this experiment is close to the biomineralization process of nacre, we hope the information revealed in the present study will help understand the growth mechanisms of the nacre in shell.更多还原