滴定过程控制Mg(OH)2晶体粒径和形貌

Morphology and Size Control of the Mg(OH)_2 Crystals by Different Titration Manner

以氯化镁为镁源，氨水为沉淀剂，分别采用正向、反向和双向三种滴定过程制备Mg（OH）2，通过监测溶液动态pH值变化，并引入晶体生长驱动力指标S（镁与氢氧根离子积与容度积的比值取对数）来定量表示溶液滴定过程中动态过饱和度变化，SEM和XRD表征Mg（OH）2的结构和形貌。结果表明，正向滴定过程合成的Mg（OH）2晶粒大小混杂（100～600nm），反向滴定合成的晶粒偏小（200nm左右），双向滴定合成的晶粒粒径分布集中（400nm左右）。引入的S值较能准确地描述Mg（OH）2成核和晶体生长的规律，不同的滴定过程有不同的S值变化规律。联系S值的变化和晶体粒径的分布，认为S〉0时晶体成核占主导，S〈0时晶体生长占主导。通过动态控制溶液S值的动态变化，可以目的性地控制Mg（OH）2晶体的结构和形貌。

Magnesium hydroxide was prepared by ordinal-titration method, reverse-titration method and double-titration method, pH of the solution was controlled during the titration process, and S value, which point to the growth of Mg （OH）2 crystal force, was used to show the dynamic variation of supersaturation in quantity. The samples were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD）. The results show that the Mg（OH） 2 by ordinal-titration was made up of the larger particle （600 nm）and smaller（-100nm） , while the particle size was decreased to 200 nm by reversetitration, and centered at 400 nm by double-titration. S value was obviously different in the three titration processes, and it could be used to describe the growth of Mg（OH） 2 crystal more exactly. Compared the S value with the particle size distribution of Mg （OH） 2, it can be inferred that when S 〉 0, nucleation is dominant ;S 〈 0, growth is dominant. Therefore, the morphologies and sizes of Mg （ OH ） 2 could be controlled by tuning the S value.