液相法合成针状镁铝水滑石纳米晶的研究

研究了合成条件(原料种类、加料次序、NaOH浓度和合成温度)对液相法制备镁铝水滑石试样的相组成的影响.以MgCl₂为镁源、NaAlO₂为铝源、NaCO₃和NaOH为沉淀剂,在常压下采用液相法制备了长度约100nm、直径约10nm的Mg₆Al₂(OH)₁₆CO₃-4H₂O针状纳米晶体.并且发现:可溶性原料的选取、最后加入MgC_l2的加料次序、>45℃的合成温度和保证反应溶液的pH>12,是瞬间生成镁铝水滑石纳米晶的充分必要条件.提出镁铝水滑石纳米晶核形成的过程是:均匀分布于溶液中的Al₁₃(OH)₃₂⁷⁺迅速吸附于带羟基OH-的无定型态的Mg(OH)₂表面,并进行Al³⁺扩散,为平衡电价,CO₃^2-也扩散进入Mg(OH)₂,从而在瞬间完成镁铝水滑石晶核的形成.

Preparation of Acicular Nanocrystalline Mg,Al-hydrotalcite by LiquidMethod

The acicular nanocrystalline Mg, Al-hydrotalcite flame-retardant agent, its length being about 100nm and its diameter being about 10nm, was prepared by the liquid method at normal atmosphere. The effect of preparation technology, which includes the raw material choice, adding raw material sequence, NaOH concentration, and nucleation temperature, on its phase composition was discussed. And it is found that the sufficient condition of obtaining nanocrystalline Mg, Al-hydrotalcite is as follows: (1) raw materials must be solubility; (2) pH value of the reaction solution must be greater than 12; (3) the nucleation temperature must be higher than 45℃; and (4) the adding raw material sequence must be that adding raw material MgCl₂ follows the other three raw materials. Moreover, it is put forward that the nucleation process of nanocrystalline Mg,Al-hydrotalcite is as follows: firstly, Al₁₃(OH)₃₂⁷⁺ ions are attracted on the surface of amorphous Mg(OH)₂ and Al³⁺ ions diffuse in the Mg(OH)₂; secondly, CO₃^2- is inserted in the framework for the balance of the electron valence; finally, the nucleation of nanocrystalline Mg,Al-hydrotalcite is quickly finished.