南京大学学报（自然科学版）2009，Vol.45Issue(5)：570-575,6.
纳米金属钴/膨胀石墨复合材料的制备、表征及其电磁屏蔽性能
Preparation, characterization, and electromagnetic shielding effectiveness of the composites of nano-particles of Co dispersed on expanded graphite
摘要
Abstract
Electromagnetic shielding involves the reflection and/or absorption of electromagnetic radiations by electromagnetic materials. Nowadays, electromagnetic radiations emanate from a wide variety of sources that interfere with electronic devices and affect the health of people. Thus, the radiation shielding at wide frequency range with high effectiveness is increasingly required to meet the high demand of today's society for the reliability of electronics and the health of people. Expanded graphite (EG) has been found to be a highly effective electromagnetic shielding material in the range of 1～2 GHz because of its excellent electrical conductivity. The primary mechanism of electromagnetic shielding of EG is the reflection loss due to its high conductivity, and thus its shielding effectiveness (SE) decreases sharply with the decrease of frequency. The absorption loss is a function of the product of electrical conductivity and magnetic permeability relative to copper. Thus, the metals with high magnetic permeability may play the role of absorbing electromagnetic radiations, especially at low frequencies. The composite materials of EG and magnetic metals may exhibit both absorption and reflection losses and increase the shielding effectiveness ultimately in a wide range of frequencies. In addition, there are more advantages when EG is used as a component of electromagnetic materials since it is light, flexible, corrosion resistant, and cost effective, which may make the composites more attractive than the traditional polymermatrix composites. The composites with nano-particles of cobalt dispersed on the nano-layers of expanded graphite (EG) were prepared by the impregnation of EG with ethanol solutions of cobalt acetate, followed by drying and reduction in H_2. The cobalt loadings on EG were varied up to 60% by weight. The spherical particles of Co were found to be well spread on the layers of EG with sizes of mainly 300～l 000 nm. The ratio σ_r/σ_r of the composites was found to be 0. 26～0. 33, indicating their soft magnetic properties. Since EG is of high electric conductivity, it exhibited high shielding effectiveness for electromagnetic radiations at high frequencies. The addition of magnetic Co significantly improved the shielding effectiveness at low frequencies. The electric and magnetic conductivities of the composites could be monitored through regulating the loadings of Co on EG, and it was found that the composites with 10%～40% of Co exhibited good SE. Specifically, the composite with 30%Co in EG reached the shielding effectiveness of 62 ～110 dB at the frequencies from 300 kHz to 1. 5 GHz.关键词
电磁屏蔽/纳米金属钻颗粒/膨胀石墨Key words
shielding effectiveness/ nano-particles of Co/ expanded graphite分类
信息技术与安全科学引用本文复制引用
邢晓玲,黄玉安,黄润生,唐涛,徐铮,沈俭一..纳米金属钴/膨胀石墨复合材料的制备、表征及其电磁屏蔽性能[J].南京大学学报（自然科学版）,2009,45(5):570-575,6.基金项目
国家"863"项目(2006AA03Z458).国家自然科学基金(20673055),江苏省科技厅高技术项目(BG2006031) （2006AA03Z458）
