Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Research about Synthesis and Application of Magnesium Borate and Aluminum Borate Nanowiskers

Author MoZhaoJun
Tutor TangChengChun
School Hebei University of Technology
Course Materials Physics and Chemistry
Keywords nanotechnology nanowhisker aluminum borate magnesium borate magnesium alloy boron nitride hydrothermal method sol - gel method
CLC TB383.1
Type Master's thesis
Year 2011
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Nano-materials is a new material and have some special characteristicscompared with the conventional materials and broad application prospects. Thisarticle mainly studied about the synthesis of magnesium borate and aluminumborate nanowhiskers and the initial work of aluminum borate nanowhiskersapplicated in magnesium alloys.1、Magnesium borate nanowhiskers was synthesized by hydrothermalsintering. First alkaline magnesium borate nanowhiskers was synthesized byhydrothermal, and then heat-treated to obtain magnesium borate nanowhisker. Theresults showed that alkaline conditions favor the vertical growth of nanowhiskers, alarge aspect ratio nano-whiskers could been got in strong alkaline conditions. Atthe same time, as the reaction time longer, aspect ratio of nanowhiskers got larger,but the reaction time also had an impact on the lateral nanowhiskers. Whiskersmerged with each other and grown nano-films, which is not conducive to thegrowth of nano-whiskers. There reaction temperature was a very importantinfluence on the growth of nano-whisker, only when reached a certain temperaturevalue, it would generate nano-whiskers. In the heat treatment process, untile thereaction temperature reached 700°C, the magnesium borate nanowhiskers got abetter crystallinity. Whiskers fractured in the dehydration process, and not changedin the recrystallization process; additional, it is a very important relationship toheated-rate on the fracture of whiskers, more quickly heated rate the more seriousfracture of nanowhiskers. Finally, magnesium borate nano-film was prepared byadjusting the reaction conditions. The result showed that the concentration ofresponse has an important effect on magnesium borate nano-film, the higher theconcentration, the smaller nano-film.2、Large quantities of BN-coated aluminum borate (Al18B4O33) nanowhiskerswith typical 20-50 nm in diameter and 0.5-2μm in length have been successfullysynthesized by sol-gel and post-thermal-treatment methods. Al4B2O9 nanowhiskerswere first prepared at a relative low temperature, and converted into Al18B4O33phase at higher temperature in the air due to their high-temperature instability.Besides Al18B4O33 phase, Al5BO9 and B2O3 could be generated in the process oftransition. However, Al5BO9 and B2O3 phases could be dispelled if Al4B2O9 wasconverted into Al18B4O33 phase at higher temperature under NH3 flow.Simultaneously, a uniform BN layer was coated surrounding (on) the nanowhiskers. The temperature to introduce NH3 was shown as an important factor to retain thenanowhisker morphology of Al18B4O33. The formation of BN coating was a resultof the interfacial reaction between NH3 and boron oxide in-situ generated duringthe transformation from Al4B2O9 to Al18B4O33. This ensures that the BN layerswere attached tightly on the surface of the synthesized Al18B4O33 nanowhiskers.3、BN-coated Al18B4O33 nanowhiskers and aluminum could be finely adhesiveinfiltration. The Al18B4O33 nanowhiskers would be better dispersed in magnesiumalloys by preform of the Al18B4O33 nanowhiskers and the aluminum. The hardnessof Al18B4O33 nanowhiskers reinforced magnesium alloy was greatly improved, andstill maintained the ductile fracture.

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