| The research of magnesium hydroxide (Mg(OH)2) flame retardant with excellent performance is one of the most important topic in the magnesium compounds of chemical products. In order to promote the industrial production of Mg(OH)2 flame retardant, with consideration of production costs and environmental effects, the crystallization process and crystallization behavior of Mg(OH)2 crystal have been deeply studied on the basis of the crystallography theory in this thesis. The solution synthesis methods are adopted to control the growth habit of Mg(OH)2 microparticles, and thus to achieve the morphology control and the properties optimization.The high-quality Mg(OH)2 flame retardant with hexagonal nanoplate morphology has been prepared by a magnesium-chloride-ammonia strategy. The morphologies and structure information of Mg(OH)2 products sampled in different periods were characterized by Scanning Electron Microscope (SEM) and X-ray powder diffraction (XRD). Moreover, a series of operational parameters have been investigated in this work. The results reveal that some factors, for example filtration of ammonium chloride, composition of hydrothermal solvent, hydrothermal time, hydrothermal temperature have an important effect on the morphology of final products and the performance as flame retardant. The conclusion can guide the further theoretical research and industrial production of Mg(OH)2 crystal.A new self-templated strategy has been designed to prepare Mg(OH)2 crystal. The precursor Mg-Al layered double hydroxide (Mg4Al2(OH)12CO3·3H2O) was transformed into Mg(OH)2 crystal in alkali solution under hydrothermal condition. Moreover, the transformation process has been characterized using SEM and XRD. The results indicate that the self-templated strategy can be extended to fabricate other metal hydroxides.The probable growth mechanism of Mg(OH)2 crystal has also been discussed in this work, which includes the dissolution-recrystallization of amorphous Mg(OH)2 and the hydration-crystallization of magnesium metal. The result shows that the coordination structure of Mg2+ determines the final morphology of Mg(OH)2 crystal. The current work opens a door for the further design of the crystallization process of Mg(OH)2 and optimization of the industrial production of Mg(OH)2 flame retardant.
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