Study On The Synthesis Technology Of Magnesium Hydroxide Hexagonal-shaped Micro/Nanocrystals

Micro/nano magnesium hydroxide (MH) materials have received a great deal of attention owing to their application in a wide range of fields such as water treating, paper conservation, solar cells, and desulphurization. Especially MH is a nontoxic, noncorrosive, antacid, thermally stable and environment-friendly flame retardant, undergoing endothermic dehydration and suppressing fume under fire conditions. These applications originate from the unique physical and chemical properties of MH which depend not only on the shape but also on the size and dispersion. Especially, the lamellar-like MH is a good candidate for functional polymeric composites and fiber hybrid materials, as a reinforcing agent or halogen-free flame-retardant. It was also confirmed that the addition of lamellar-like MH retarded the onset decomposition temperature of polymers, enhanced the thermal stability of it. Preparation of high quality lamer-like MH is one of the most promising research topics. In this dissertation, systematic explorations have been carried out on new synthetic technology of functional inorganic micro/nano MH crystals based on hydrothermal method. The main points can be summarized as follows:Based on the oxygen affinity properties of Mg2+ion, the oxygenates-assisted hydrothermal crystallization technology has been designed to obtain MH hexagonal nanosheets with perfect crystallinity, regular shape, and monodispersity. Glucose and K2C2O4 contains multiple active oxygen atoms. The central features of our approach are the use of glucose as capping agent to control the reaction in the precipitation stage and the use of K2C2O4 as structure-directing agent in subsequent hydrothermal treatment for morphology controlled. The average diameter of crystals can be facilely controlled by varying the types and concentration of the alkali.MH hexagonal nanosheets with high-dispersion are successfully prepared through a one-pot synthesis without titration process. The K2C2O4 was used to control the growth of crystal in the c direction (direction perpendicular to the layers) and to modify the surface property of the MH particles in hydrothermal treatment. It was also confirmed that high-concentration NaNO3 solution can increase chemical formula in this system which speed up chemical reactions and show a strong influence on morphological control of final products. Morphologic transformation from sheets to disks can be observed by increasing reaction time. Based on common-ion theory, MH hexagonal-shaped sheets have been successfully synthesized via adding sodium acetate in titration phase which play important role in nucleation of an initial'seed'and growth and using magnesium chloride solution in hydrothermal treatment. To understand the effect of solvent on crystallization, some species including CH3COONH4, H2O, CH3CH2OH, (CH3)2CO, cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS) were systematically investigated. CH3COONH4 solution with different concentration as a hydrothermal modifier has important effect on dissolution-recrystallization process.