Hydrothermal Synthesis And Characterization Of Magnesium Borate Whiskers And Magnesium Hydroxide

Nanostructured Magnesium borate and Magnesium hydroxide has excellent mechanical properties, high temperature, corrosion resistance, unique strengthen' property and flame-retardant property and they have important application value on improveing performance of the metal, plastic and ceramic composites. Magnesium borate and Magnesium hydroxide are important functional materials with wide application prospect.In this paper, the preparation technology of Nanostructured Magnesium borate and Magnesium hydroxide was researched; The influence of reaction temperature, reaction time, concentration and surfactant conditions on performance of the products were investigated; XRD, SEM, FT-IR, TG were employed to characterize the structural feature, morphology, chemical composition and thermal behavior of the products. The optimized hydrothermal synthesis process conditions of them were obtained and also their growth processes were discussed.Magnesium borate hydroxide whiskers was prepared by using a hydrothermal method with MgCl2·6H2O, Na2B4O7·10H2O, NH3·H2O and adding dispersant into the reaction system. The experiment results showed that it was MgBO2(OH).The effect of operational parameters such as concentration, material ratio, reaction temperature, reaction time, surfactant on the composition and morphology of the products were studied. The optimum condition were:the concentration of MgCl2·6H2O:1.67 mol/L, Na2B4O7·10H2O:0.31mol/L, NH3:6.3mol/L, reaction temperature:190℃, reaction time:10h. MgBO2(OH) has a aspect ratio of 30-90, a diameter of 60-90, length 3-7μm and good dispersibility. Magnesium borate whiskers (Mg2B2O5) with aspect ratio of 50-80 were then obtained by calcining of the precursor at 700℃for 3h due to water loss.Magnesium borate hydroxide whiskers growth process was studied under dissolution recrystallization mechanism of hydrothermal method. Magnesium borate whisker growth is a multi-step reaction by ions selective on specific crystal face, it was then sintered to achieve Magnesium borate whiskers.Magnesium hydroxide nano-plates was prepared by using a hydrothermal method with MgCl2·6H2O and adding dispersant into the reaction system.The effect of operational parameters such as reaction temperature, reaction time, surfactant on composition and morphology of the products were studied. Magnesium hydroxide hexagonal plate with a thickness of 20-50nm and a diameter of 200-300nm was prepared when the concentration of MgCl2·6H2O:1.67 mol-L, NH3·H2O: 6.3mol/L.Magnesium hydroxide hexagonal plate growth is dissolution recrystallization mechanism too. Magnesium hydroxide gradually dissolved as the temperature increasing. Mg2+ and OH- continued to gather into embryos, embryos formed a certain size nuclei, thus Magnesium hydroxide nano-plates was generated finally.