Preparation And Study Of Electromagnetic Interference Shielding Materials Comprised Of Soft Magnetic Alloy Coated On Carbon Fiber

With the development of science and technology, humanity has entered the information society. The electromagnetic wave becomes the important carrier of information dissemination and has permeated all aspects of life. Meanwhile electromagnetic interference and radiation pollution become a serious problem. In order to address these problems, electromagnetic shielding technology is received increasing attention in many countries. In recent years, electromagnetic shielding composite materials are developing toward efficient, lightweight and low cost. In this paper biocarbon nanofibers were obtained using low cost and environmentally friendly bacterial cellulose. The dielectric loss and magnetic loss of biocarbon fiber comparing to magnetic metal are small. So the important content of this article is that how to use the metal coating method to improve the dielectric loss and magnetic loss of biocarbon fiber. The introduction of magnetic metal particles onto biocarbon nanofiber has previously been shown to lead to good dielectric loss and magnetic loss,and the original characteristics of biocarbon fiber was not damaged due to the process of metallization. In this article electromagnetic interference shielding materials comprised of Ni–Co coated on biocarbon nanofibers were successfully prepared by electroless plating. The morphology, composition, phase, conductivity, static magnetic, dynamic magnetic and electromagnetic interference shielding efficiencies of the composites were investigated. The main contents of research are as follows:The preparation of biocarbon fiber: The freeze drying and direct drying bacterial cellulose are carbonized under different temperatures respectively. The experimental results show electromagnetic shielding efficiency of biocarbon fiber obtained by heat treatment of freeze drying bacterial cellulose at 1200°C was the best.The EDS spectrum showed that the carbon content in biocarbon fiber is 95.45 wt %.In the diffraction pattern of biocarbon fiber, a broad and weak peak at 2θ = 24.35o is observed, which is assigned to the(002) plane of graphitic carbon fiber.Pretreatments of the biocarbon fiber: The pretreatments procedure of biocarbon fiber consisted three stages: oxidation, sensitization and activation. After pretreatments process, high catalytic activity metal deposited on the biocarbon fiber surface can make the subsequent electroless reaction successfully. After oxidationtreatment, hydrophilic group(- OH) on the surface of biocarbon fiber can be found in the infrared spectrum, which can improve metal bonding force between the coating and biocarbon fiber.Electroless plating: This paper studies that NiCo alloy nanoparticles with different molar ratios of Co:Ni coated on the surface of biocarbon nanofibers have an effect on electromagnetic shielding effectiveness. The composition and operating conditions of electroless plating are as follows: cobalt sulfate(CoSO4·7H2O) 0.033 M, nickel sulfate(NiSO4·6H2O) 0.067 M, sodium phosphite(Na2H2PO2·H2O) 0.3 M, sodium citrate( Na3C6H5O7·2H2O) 0.27 M, ammonium sulfate((NH4) 2SO4) 0.37 M, pH =9, which were carried out at 35°C for 15 min. Biocarbon nanofibers with NiCo coating were amorphous state by electroless plating. The experimental results show that heat treatment can change static magnetic, phase structure, conductivity and electromagnetic shielding effectiveness of biocarbon nanofibers with NiCo coating.The electromagnetic shielding effectiveness: Conductivity, dielectric constant and the electromagnetic shielding effectiveness of the shielding materials will increase with Ni Co coated on biocarbon nanofibers loading. Electric conductivity and dielectric constant of Ni Co coated on biocarbon nanofibers are often greater than pure biocarbon fiber. The shielding materials containing 30 wt% NiCo coated on biocarbon nanofibers showed absorption loss and the reflection loss was shown to be ca. 37.3dB and 3.9 dB at 12.4 GHz, respectively and showed the highest electromagnetic shielding effectiveness of 41.2 dB(99.99% attenuation). Among the absorption loss is the primary factor governing electromagnetic shielding.