单分散纳米氢氧化镁晶须制备及形成机理研究

The nanometer magnesium hydroxide whiskers has been one of the most prospective functional materials of inorganic flame retardant. However, the application has been restricted because of the accumulation phenomena during the crystallization and high cost during the preparation. In this project, the new material of monodispersed nanometer magnesium hydroxide whiskers is prepared taking magensite as raw material by means of controlling on microthermal calcination, hydro-thermal synthesisan, predecessor materials and so on. The influence laws of the magnesia activity, the dispersity and shape of the predecessor materials, the various reactive conditions and assistant agents during hydro-thermal synthesis on the dispersity and slenderness ratio of nanometer magnesium hydroxide whiskers are studied systematically, through the kinetic controlling during the calcination, the orientation controlling of nucleation growth and adjusting surface polarity of the whiskers during hydro-thermal synthesis, through the optimum design by the addition agents to control crystal face energy and decrease of surface polarity of the final product. Finally the optimum preparing technology, the kind and amount of additives of the decentralized nanometer magnesium hydroxide whiskers with low surface energy can be determined. The formation mechanism of monodispersed nanometer magnesium hydroxide whiskers is then explored under the hydrothermal condition. In addition, by applying the theories of crystal chemistry, surface chemistry, reaction dynamics and so on, the detection restults of whiskers dispersion and slenderness radio, and the dynamic parameter results of reaction system parameters during the reaction process are analysed and theoretically calculated. The surface reaction of the crystal nucleus is researched and the microstructure molecular configuration of the surface of magnesium hydroxide whiskers is established. The decentralized mechanism of the nanometer magnesium hydroxide whiskers is explored.

纳米氢氧化镁晶须是极具发展前景的无机阻燃剂功能材料之一，但因晶须聚集严重而限制了其应用。本项目以菱镁矿为原料，通过低温煅烧、水热合成、前驱物控制等手段制备单分散纳米氢氧化镁晶须新材料。通过煅烧过程动力学的控制，水热合成过程中晶核生长取向和晶须表面极性的调控，采用合成过程动态取样观察分析并检测反应体系表面能等参数的方法，通过添加助剂调控晶面能及表面包覆降低晶体表面极性等优化设计，系统研究氧化镁的活性、前驱物的分散性及形貌、水热合成反应参数及助剂等因素对纳米氢氧化镁晶须分散性及长径比的影响规律，确定最优制备工艺及助剂与用量，搞清单分散纳米氢氧化镁晶须水热反应条件下的形成机理。运用晶体化学、表面化学及反应动力学等相关理论，对晶须检测观察分析结果和反应体系参数动态检测数据等进行理论计算与分析，研究晶核表面反应，建立纳米氢氧化镁晶须表面微观分子构型，探明纳米氢氧化镁晶须的分散机理。

纳米氢氧化镁（简称纳米MH）晶须因其无毒、无味、分解温度高等特点而成为一种极具发展前景的环境友好型无机阻燃剂材料之一，但因其晶须表面极性较强容易聚集且制备成本偏高而限制了其具体应用。本项研究的主要内容包括：以优质菱镁矿为原料，通过煅烧过程动力学控制，制备出了活性良好的氧化镁；在水热合成过程中控制晶核生长和晶须表面极性，动态取样观察分析晶须的形貌，优化设计表面改性助剂的种类、加入方式及数量，调控晶体表面能，制备出分散性好的产物。重点探索了氧化镁的活性、氢氧化镁（MOS）前驱物的分散性及形貌、水热合成反应参数及助剂硬质酸钠的用量等因素对MH晶须分散性及长径比的影响规律，确定了最优制备工艺与方法。研究得出：（1）通过MOS晶须和纳米MH晶须制备过程动态取样，检测体系中SO42-浓度或OH-的浓度，利用MATLAB软件，结合动力学方程，建立了MOS晶须和纳米MH特定的生长模型，MOS晶须生长模型与MB-2模型拟合较好；纳米MH晶须形成的动力学模型为MA-2；（2）MOS晶须和纳米MH晶须结晶速率受表面反应控制，结晶动力学为多核控制表面生长，成核诱导期短；（3）建立了MOS晶须和纳米MH晶须动力学方程模型；（4）通过SEM图的观察分析认为，MOS晶须在成核长大过程中其尖端存在生长台阶，推断其生长方式为沿着轴向螺旋位错生长；纳米MH晶须形成过程既包括以MOS为模板的模板机制，又包含液固机制下的螺旋位错生长机理。本项研究的关键数据主要体现在制备方法中各相关参数的优化与控制，一步法完成了纳米MH晶须的制备及改性。本项目研究从理论上弄清了MOS晶须和纳米MH晶须在水热合成反应中的成核长大机理，以及控制表面极性的具体方法，解决了晶须团聚，制备出了分散性好、长径比高的纳米MH晶须材料，所获得专利技术为其产业化和具体应用提供了技术条件，为我国无机阻燃剂的产业化应用奠定了良好的技术理论基础。