| The study of high-quality magnesium functional materials is one of the most interesting topics in the field of materials due to their important applications in environmental protection, flame retarding,medicine and catalysts The performance of these materials is closely related to their size and morphology.Accordingly,the morphology and size control of magnesium functional materials is one of the most important research subjects.We developed some new preparation technologies for magnesium hydroxide sulfate hydrate,magnesium hydroxide and magnesium oxide,and their morphologies and sizes were successfully controlled.A new alkaline buffer solution system including Mg2+,SO42-,NH4+ and diethanolamine was designed,in which Mg(OH)2 nanoparticles can be homogeneously precipitated under a hydrothermal condition.These Mg(OH)2 nanoparticles can be converted into 5Mg(OH)2·MgSO4·2H2O(512MHSH) whiskers with uniform size and shape,an aspect ratio no less than 100 by the direction of SO42- ions.The average diameter of whiskers can be facilely controlled from 4μm to 50 nm only by adjusting the concentration of reactants and without varying any other experimental parameters.The growth mechanism of 512MHSH was discussed by analyzing the experimental results,which contributes to more profound understanding of 512MHSH growth habit.In order to improve the compatibility between inorganic materials and polymer,the surface of as-prepared whiskers was modified by using sodium stearate.A controllable system of anion exchange between SO42- and OH- ions,which includes glycerol and NaOH,was designed to fabricate Mg(OH)2 whiskers in a normal atmosphere at 80℃using 512MHSH obtained above as precursors.The morphology of as-synthesized Mg(OH)2 whiskers is similar to that of precursors.The addition of a little glycerol is vital not only to perfectly maintain the morphology of precursors but also to ensure conversion efficiency in this system.The controllable anion exchange mechanism was discussed on the basis of the theoretical and experimental analysis.The functional Mg(OH)2 powder with high crystallinity,good dispersibility, homogeneous granularity and hexagonal shape was successfully synthesized by using a new compound hydrothermal modifying agent including citrate and NaOH.The Mg(OH)2 powder was modified by using sodium stearate,and its surface became hydrophobic.The growth mechanism of Mg(OH)2 crystal in hydrothermal condition was also discussed.The functional MgO powder with the same morphology was prepared by hot-treatment of Mg(OH)2 powder. The exposure of crystal surface with high catalysis activity is distinctly enhanced.The as-prepared 512MHSH and Mg(OH)2 whiskers with controllable diameter,which have dual functions as flame retardant and reinforcing materials,are the perfect additive for polymer.The functional Mg(OH)2 powder is a kind of high-quality flame retardant,which can also find application in catalysis,medicament,environmental protection,etc.The functional MgO powder with high activity crystal plane may be an excellent catalytic material. In addition,both new preparation technologies and growth mechanisms mentioned in this paper can provide useful references for fabrication of other micro/nano-materials.
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