【作者】 赵丽；

【导师】 赵修建； 余家国；

【作者基本信息】 武汉理工大学 ， 材料学， 2003， 硕士

【摘要】 由于二氧化硅球形颗粒在光子晶体、催化剂载体、色谱填料、标准计量等许多高新技术领域有着非常广泛的应用前景。本文用醇盐水解法和聚合诱导胶体团聚法分别制备了纳米和微米二氧化硅球形颗粒，并对其结构和制备条件进行了详细研究。 在醇水混合溶剂中以氨作催化剂，正硅酸乙酯（TEOS）为硅源，通过溶胶-凝胶水解工艺制备出单分散二氧化硅球形颗粒，通过透射电镜（TEM）进行研究各种反应条件如溶剂类型、氨和水的浓度、水解温度等对二氧化硅的颗粒大小和形貌的影响。结果显示：以甲醇和乙醇为溶剂可以形成单分散的二氧化硅纳米球形颗粒，以丙醇和丁醇为溶剂，二氧化硅纳米球形颗粒容易聚集；在其它条件不变的情况下，纳米球形颗粒的粒径随水和硅源的浓度增加而增大；而且水解温度的升高，生成的颗粒粒径也逐渐增大，仔细研究和讨论了二氧化硅颗粒在不同反应条件下的形成机理。 研究了酸、碱催化剂对TEOS水解速率及硅溶胶形貌的影响，发现只有在碱性催化剂下可制备出单分散二氧化硅纳米球形溶胶粒子，而在酸催化剂下制备出的二氧化硅具有三维网络结构的溶胶。这归因于在酸催化TEOS水解反应过程中，水解的速率是越来越慢，水解的中间产物同时进行缩聚反应，形成高度缩聚的三维空间网络结构；在碱催化TEOS水解反应中，水解的速率是越来越快，只有当完全水解后，中间产物才开始进行缩聚反应，所以形成单分散球形颗粒。 在二氧化硅溶胶中，通过尿素和甲醛在酸性条件下的聚合反应，用聚合诱导胶体团聚法（PICA）制备出有机无机（尿醛树脂／SiO₂）复合微球，高温煅烧后获得了多孔SiO₂微球。用扫描电子显微镜（SEM）观察了煅烧前后微球的表面形貌，大小和分布，用差示量热和失重分析（DSC-TG）研究了有机无机复合微球的脱水、脱醇及有机物炭化分解的过程，用氮吸附法测量了多孔微球在煅烧前后的比表面积变化；用激光粒度分布仪（PSD）测量了微球在煅烧前后的平均粒径和粒径分布。结果发现：尿素和甲醛在酸性条件下自身聚合可以形成高分子微球，获得的高分子微球的粒径范围较宽且有团聚现象，而用PICA法制备的有机无机复合微球粒径范围较窄且团聚现象不明显;反应过程中溶液必须均匀搅拌，如果不搅拌颗粒之间易出现团聚，如果搅拌的速率过快，刚聚合形成的微球容易被打散，破坏了微球的球形度和形貌:干燥和焙烧的升温速率不能太快，否则会出现团聚和微球开裂的现象。对球形颗粒的形成机理分析表明，尿素和甲醛在酸性条件下聚合成线型有机高分子，由于相分离作用，逐渐从溶液中脱离出来，在二氧化硅溶胶中，有机低聚物以范德华力和氢键作用吸附到胶粒表面，使胶粒从溶胶相中分离到有机物相中，在溶液中形成有机无机复合微球。更多还原

【Abstract】 Silicon dioxide spherical particles are widely used in many fields of advanced technology, such as photonic crystals, catalyst supports, chromatographic packing materials and standard materials in measurement etc. In this article, nanometer and micrometer SiOi spherical particles were synthesized by hydrolysis of alkoxide and polymerization-induced colloid aggregation process, respectively. Also the structures of microspheres and preparation conditions were detailed studied.Monodispersed silicon dioxide spherical particles were prepared by hydrolysis of tetraethoxy silane (TEOS) in alcohol-water mixed solvents using ammonia as a catalyst. Effects of the type of solvents, the amount of water, the concentration of ammonia and temperature of hydrolysis etc. on the particle size and morphology of SiOa were investigated by transmission electron microscopy (TEM). The results show that the minodispersed silicon dioxide spherical particles could be obtained hi methanol or ethanol solvent, while agglomerated silicon dioxide particles were formed in n-propanol and n-butanol solvent. When the concentration of water and TEOS is increased or the temperature of hydrolysis is raised, the particle sizes increase. The formation mechanisms of the resultant SiCh particles under different reaction conditions were carefully investigated and discussed.The effects of acid and base catalyst on the rate of hydrolysis and morphologies of sol were investigated, the results show that monodispersed silicon dioxide spherical particles were obtained using base as catalyst, while silica sol of highly condensated three-dimensional network were obtained with acid as catalyst This is ascribed to the fact that during the hydrolysis of TEOS the rate of hydrolysis was slower and slower when acid is used as catalyst, at the same time, the midterm products began to condense and then formed highly condensated three-dimensional network. While when base is used as catalyst, the rate of hydrolysis was faster and faster, during hydrolyzing the midterm productsbegan to condense and form monodispersed silicon dioxide spherical particles.Porous silicon dioxide spherical particles were synthesized by polymerization- induced colloid aggregation (PICA). Polymer-based composite microspheres (urea-formaldehyde /SiOa) were obtained in silicon dioxide sol by the polymerization reaction of urea and formaldehyde in acid condition, and then formed porous microspheres after sintering. The morphology, size and size distribution of microspheres before and after sintering were investigated by using scanning electron microscopy (SEM). The desorption of water and ethanol and decompostion of polymers in microspheres were analyzed by using TG-DSC machine. The specific surface area before and after sintering were measured by nitrogen adsorption. The average particle size and size distribution were measured with laser particle size analyzer. The results show that urea and formaldehyde in acid solution can polymerize and form polymer microspheres with broad size distribution, however, many particles clustered together. In contrast, in the PICA process, composite microspheres appear a very narrow particle size distribution and have minimal particle aggregation. Mechanical agitation during particle growth can inhibit clustering of the aggregates. Microspheres will be destroyed due to over-agitation. The temperature of dry and sintering rose slowly in order to prevent the forming of clusters and crack of microspheres. By analysis of microsphere formation mechanisms, the results show that urea and formaldehyde undergo acid-catalyzed polymerization, and oligomers gradually separate from solution due to phase separation. In silicon dioxide sol, the oligomer is adsorbed on the surface of colloids by Wan der walls force and hydrogen bonding, then forms Polymer-based organic/inorganic composite microspheres in solution.更多还原