【作者】 陈晶；

【导师】 赵素玲； 王一龙；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 硕士

【摘要】 电磁屏蔽材料在民用及军用领域有着广泛的应用,已经成为民用防电磁波辐射和各国军事装备屏蔽等技术领域研究的热点。本文以Schelkunoff电磁屏蔽理论为指导,针对目前单一导电或导磁型电磁屏蔽剂难以在较宽频率范围内具有良好的屏蔽效果的问题,在前人的研究基础上设计出以片状羰基铁粉为内核粒子,采用化学镀法制备得到片状Fe@Ag核壳复合粒子,并比较了片状Fe@Ag核壳复合粒子和球形Fe@Ag核壳复合粒子作为电磁屏蔽橡胶的填料时,对电磁屏蔽橡胶性能的影响。为进一步提高Fe@Ag核壳复合粒子的电性能和电磁屏蔽效能,对其进行了低温热处理。本研究达到了预期的研究目标,取得了以下主要的结论：1.选择片状羰基铁粉为内核粒子,葡萄糖为还原剂,采用化学镀法制备了片状Fe@Ag核壳复合粒子。由于金属粒子间的点阵常数相近,接触角小,它们之间的界面能比较低,成核时体系自由能的增值小,所以银粒子在羰基铁粉表面的成核率高。且由于金属本身是具有催化活性的表面。所以不需要对内核粒子进行任何预处理就能够得到具有完整壳层结构的核壳复合粒子。通过控制反应条件来控制银粒子的还原反应的速率,使银颗粒在铁粉表面异相成核生长,形成致密、均匀的银壳层。2.利用有效介质理论计算证实了以片状粒子作为填料的电磁屏蔽橡胶的渗滤阈值较小,片状粒子间更容易形成导电网络。实验证明：片状Fe@Ag核壳复合粒子作为填料的电磁屏蔽橡胶的体积电阻率为4.87×10-3Ω·cm,屏蔽效能为-51 dB～-55 dB。比球形粒子作为填料的电磁屏蔽橡胶的体积电阻率提高了78%,屏蔽效能的数值降低了-6 dB～-19 dB,屏蔽效果更好。3.为降低Fe@Ag复合粒子的电阻率,提高复合粒子银壳层的致密度和屏蔽效能,对Fe@Ag核壳复合粒子进行低温热处理。研究证明：热处理温度并未改变复合粒子的物相结构及饱和磁化强度,但对复合粒子的电阻率和壳层致密度有较大影响,在140℃获得的Fe@Ag复合粒子的银壳层最致密,电阻率最低；但随热处理温度的升高,其电阻率和致密度反而下降；以140℃热处理后的复合粒子作为屏蔽填料制备的电磁屏蔽橡胶的SE为-28 dB～-53 dB,比未进行热处理时降低了-10 dB～-15 dB,屏蔽性能得到了提高。同时以界面润湿理论和晶体生长理论解释了热处理过程对复合粒子壳层微观形貌与屏蔽效能的影响。更多还原

【Abstract】 Electromagnetic shielding materials have been widely used in civil project and military engineering. It has become a research hotspot in civil control of electromagnetic radiation technology and military equipment shielding technology. According to Schelkunoff electromagnetic shielding theory, single conductive or permeable electromagnetic shielding agent has not a good shielding effectiveness(SE) in a wide frequency range. On the basis of the predecessors, we have prepared flaky Fe@Ag core-shell composite particles using flaky carbonyl iron particles as the core particles by electroless plating technology. And the influence of electromagnetic shielding rubber containing flaky Fe@Ag core-shell composite particles and spherical Fe@Ag core-shell composite particles on the shielding effectiveness were also studied. To further enhance electrical property and electromagnetic shielding effectiveness of Fe@Ag core-shell composite particles, we carried a low-temperature heat treatment on the composite particles. This study shows that we have achieved the desired research goals and obtained the following conclusions:1. Flaky Fe@Ag core-shell composite particles were prepared selecting flaky carbonyl iron powders for the core particles and glucose as reducing agent by electroless plating technology. Since the lattice constant of metal particles is similar, the contact angle is small, the interfacial energy between them is relatively low and the increment of nucleation free energy in the system is relatively small, there is a high nucleation rate for silver particles on the surface of carbonyl iron powders. Also, core-shell composite particles do not need any pretreatments due to Metal’s surface catalytic activity. By controlling the reaction conditions to regulate the reduction rate of the silver particles, silver heterogeneous nucleation may grow up and finally the silver shell with compact and uniform structure was formed on the surface of carbonyl iron powders.2. We proved that the percolation threshold of electromagnetic shielding rubber containing flaky particles is smaller than spherical particles’by calculating its value using effective medium theory. And flaky particles more easily form a conductive network. The experiment results showed that volume resistivity of electromagnetic shielding rubber containing flaky Fe@Ag filler is 4.87×10-3Ω·cm, showing an dcrease of 78% compared to the rubber containing spherical filler. And the shielding effectiveness is-51 dB～-55 dB, a decrease of-6 dB～-19 dB in comparison with the rubber containing spherical filler.3. In order to reduce the resistivity of Fe@Ag composite particles, increase the density of Ag shell and shielding effectiveness of Fe@Ag composite particles, we carried a low-temperature heat treatment on the composite particles. The results showed that the temperature of heat treatment had nothing to do with the phase structure and saturation magnetization, but had great influence to volume resistivity and shell density. The Fe@Ag composite particles treated at 140℃have the highest shell density and a minimal volume resistivity, but as the temperature of heat treatment increasing, shell density and volume resistivity would be worse. The SE value of electromagnetic shielding rubber containing the Fe@Ag composite particles treated at 140°is-28 dB～-53 dB, showing a decrease of-10 dB～-15 dB compared to the one without heat-treatment. The effect of heat treatment to the shell morphology and related property was reasonably explained by the interface wetting theory and crystal growth theory.更多还原