| 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.
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