摘要:
利用硅烷偶联剂改性纳米SiO2,制得改性纳米SiO2分散液和改性纳米SiO2颗粒。分别利用“机械法”和“气泡法”制备纳米SiO2含量为2 wt%,3 wt%,4 wt%,5 wt%和6 wt%的未改性纳米SiO2复合环氧树脂和改性纳米SiO2复合环氧树脂,测试了复合环氧树脂的击穿特性和耐电晕特性。测试结果表明,复合环氧树脂的击穿场强和耐电晕性随纳米SiO2含量的增加而增加,击穿场强在5 wt%纳米SiO2含量时达到最大值,“气泡法”制备的改性纳米SiO2复合环氧树脂的击穿场强和耐电晕性优于所制备的其他复合环氧树脂。以5 wt%纳米SiO2含量复合环氧树脂为例,通过森下氏分散指数(Morisita’s index)方法对复合环氧树脂中纳米SiO2的分散性进行定量表征,得出“气泡法”制得的纳米SiO2/环氧树脂复合材料的分散性优于“机械法”制备的复合材料。研究发现纳米SiO2在环氧树脂基体中分散性越好,复合材料的击穿特性和耐电晕性越好。
Abstract:
Polymer nanocomposites have advantage over traditional materials in electrical properties from the standpoint of dielectrics and electrical insulation. The influences of nanoparticle dispersion in the matrix, which is mainly caused by different preparation methods, on the dielectric properties of composites have been given in the past work. In order to investigate the relationship between the dispersion of nanoparticles in the matrix and the dielectric properties of composites, nano-SiO2/epoxy composites are prepared by different methods. Nano-SiO2 is first modified by silane coupling agent to obtain nano-SiO2 powder and nano-SiO2 dispersing liquid, then unmodified and modified nano-SiO2 powder are mixed into epoxy by “mechanical mixing method”, and the modified nano-SiO2 dispersing liquid is mixed into epoxy by“bubble mixing method” to prepare nano-SiO2/epoxy composites. The amounts of nano-SiO2 content in the composites are 2 wt%, 3 wt%, 4 wt%, 5 wt% and 6 wt%, respectively. Breakdown strength and corona-resistance characteristics of the composites are tested. The results show that with the increase of the nano-SiO2 content, the breakdown strength and corona-resistance of nano-SiO2/epoxy composites increase. The maximal breakdown strength appears in the composites with 5 wt% nano-SiO2. This appearance accords with percolation theory. The composites prepared by “bubble mixing method” have better breakdown strengths and corona-resistances than the composites prepared by“mechanical mixing method”. The scanning electron microscope images of the nano-SiO2/epoxy composites are analyzed by Image J? software to obtain the information about the nanoparticle number in the special grid. Morisita’s index is used to characterize the dispersion of nano-SiO2 in the matrix quantitatively. It is concluded that the composites prepared by “bubble mixing method” have better dispersion than those prepared by “mechanical mixing method”. Compared with the unmodified nano-SiO2, modified one has good dispersion in the composite because of the improved compatibility between the nanoparticles and the matrix. Based on the role that nano-SiO2 particles block discharge from developing in the composite, the better dispersion means that there are more nanoparticles and more barriers on the discharge path. Meanwhile, the better dispersion also means that more interface areas form between nano-SiO2 and matrix. The shallower traps supplied by the interface area will contribute less energy when current carriers jump into and out off the traps. So the better the dispersion of nano-SiO2 in the matrix, the superior the breakdown strength and corona-resistance of the composites are.
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