【作者】 郭瑞；

【导师】 赵修建； 余家国；

【作者基本信息】 武汉理工大学 ， 材料学， 2004， 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。本文用聚合诱导胶体团聚法制备介孔二氧化硅球形颗粒，并对其形成机理及制备条件进行了详细研究。 在二氧化硅溶胶中，通过尿素和甲醛在酸性条件下的缩聚反应，用聚合诱导胶体团聚法（PICA）制备出单分散脲醛／SiO₂复合微球。对复合微球形成机理的研究表明，尿素和甲醛在酸性条件下自身聚合可以形成高分子微球，在SiO₂酸性溶胶中发生聚和反应时，随着反应的进行，齐聚物不断生成，SiO₂胶体颗粒逐渐吸附在齐聚物分子链上，当聚合物链达到沉淀临界链长时，由于相分离作用，从前驱物溶液中析出，同时SiO₂胶体颗粒均匀的分布在脲醛聚合物网络中，随之沉淀出来，形成脲醛／SiO₂复合微球。 通过扫描电镜（SEM）、光学显微镜研究了各种反应条件如甲醛／尿素配比R、乙醇的含量V_e、pH值、反应温度等对脲醛／二氧化硅复合微球颗粒大小和形貌的影响。结果显示：当pH=0.3～0.8，R=1～4，水溶液中乙醇体积含量（V_e）为10％～30％时，可重复获得平均粒径约为4μm的单分散复合微球。当R＜1时将导致微球产生破裂，而R＞4时则生成凝胶状物质；其他条件不变时，微球形貌随pH值的增大逐渐变差，最终破裂；乙醇含量增大时，微球粒径逐渐增大；而随着反应时间的进行，颗粒逐渐长大，微球形貌不断完善，表面逐渐平滑；反应温度的变化会得到更光滑的微球表面，微球粒径随之增大。 对脲醛／SiO₂复合微球进行热处理后得到介孔二氧化硅微球，用示差扫描量热（DSC）／热重（TG）分析研究了脲醛／SiO₂复合微球的脱水、脱醇及有机物炭化分解的过程；用氮气吸附法分析了不同pH值、热处理温度对介孔二氧化硅微球的比表面积及孔结构的变化影响；用SEM表征了不同pH值下二氧化硅微球的形貌变化。 结果发现：二氧化硅胶体颗粒均匀分布于脲醛聚合物网络中，煅烧去除有机模板后微球表面变粗糙，而粒径没有明显变化；pH值较小时，复合微球中聚合物含量较大，而pH值较大时，得到复合微球结构松散，因此热处理后的二氧化硅微球孔容及平均孔径都较大，而在pH=0.8时，得到最小值；武汉理工大学硕士学位论文随着热处理温度的变化，小于160℃时，空分布较窄，而比表面积较小，在350℃时，由于有机模板的去除，微球孔结构发生突变，比表面积明显增大，而孔径分布变宽，温度继续升高时，二氧化硅网络发生收缩，平均孔径变小而比表面积由于有机炭化物的完全去除没有太大变化;微球中的微孔在热处理过程中处于平衡状态，分布没有太大变化。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, micrometer SiO2 spherical particles were synthesized by polymerization-induced colloid aggregation process. Also the structures of microspheres and preparation conditions were detailed studied.The urea-formaldehyde (UF) polymer/SiO2 composite microspheres were prepared by polymerization-induced colloid aggregation (PICA) method. The formation mechanism of composite microspheres is attributed to the fact that that urea and formaldehyde firstly undergo acid-catalyzed polymerization to form oligomers, and then the sol particles are adsorbed on the chain of oligomers by Wan der walls force and hydrogen bonding. When the oligomers reach the critical chain length, they separate from solution due to phase separation. Polymer-based UF/SiO2 composite microspheres are obtained in the solution.The effects of formaldehyde/urea molar ratio (R), pH value, ethanol volume percent amount (Ve) and reaction temperature on the resulting microspheres have been investigated with scanning electron microscopy (SEM) and optical microscope. The results show that monodisperse UF/SiO2 composite microspheres with a mean diameter of about 4 m can be repeatedly obtained at the optimum conditions, which include the pH value of 0.3 ~ 0.8, the R range from 1 to 4 and the Ve of 10% ~ 30%. The composite microspheres will break or be involved in the result gel when R value is out of the range. And the surface of microspheres will become coarser with the increase of pH value, resulting in breakage. The variation of Ve cause the great of microspheres gradually. As for the change of reaction temperature, a good appearance of microspheres will be observed.After heat treatment we obtain the mesoporous SiO2 microspheres, the morphology, size and size distribution of microspheres before and after sinteringwere investigated by using the scanning electron microscopy (SEM). The desorption of water and ethanol and decompostion of polymers in microspheres were analyzed by using TG-DSC machine. The changes of specific surface area before and after sintering were measured by nitrogen adsorption.The results show that the surface of SiOi particles become coarser along with the remove of polymer template, but the particle size keep no change. The composite microspheres include more UF polymer under low pH value but turn into more looser under high pH value, so the result mesoporous SiOi microspheres have big pore volume and average pore size. And the value drop to the lowest at pH=0.8. As the increase of heat treatment temperature, the pore size distribution peak of SiO2 microspheres is very narrow, meanwhile the specific surface area is the smallest before 160 C. The polymer template is removed at 350 C, so the pore structure of SiO2 particles has a big change which involve the increase of specific surface area and the broaden of pore size distribution peak. With the continuous raise of temperature the SiO2 network will shrink little, as a result the average pore size will decrease, but the specific surface area has no obvious change.更多还原