Preparation And Electromagnetic Properties Of Carbon-Encapsulated Metal Nanoparticles

Since the first observation of carbon-encapsulated LaC2 by Rouff and Tomita, carbon-encapsulated metal nanoparticles (CEMNs), in particular those involving magnetic metals, have attracted substantial attention and research due to their potential applications in areas such as magnetic data storage, magnetic separation, biomedicines and microwave electromagnetic wave absorbents. Carbon-encapsulated metal nano- particle is a new type fullerene nanocomposite material which the outer carbon layers surround the metal nanoparticles exhibit well-constructed core/shell structure. For some carbon-encapsulated magnetic metal (e.g. Fe, Co, Ni) nanoparticles, the specific core/shell structure which the inner material is magnetic unit and the outer carbon layers exhibit some electrical conductivity, will effectively provide magnetic loss and dielectric loss and enhance EM absorption properties.In our study, Carbon-encapsulated Fe/Fe3C, Co, Ni nanoparticles with different morphology have been successfully synthesized with pheolic-formaldehyde resin as carbon source, ferric nitrate as metal precursors and hexamethylenetetramine as curing agent by a modified carbonization method. The morphology, microstructure, magnetic properties and microwave absorption properties of the resulting nanoparticles were characterized by TEM, HREM, XRD,VSM and vector network analyzer. Our research mainly focus on the relation of electromagnetic properties between different products and their absorption mechanism.It was observed that via carbonization at 700℃the metal core encapsulated in the carbon shell was Fe3C and the size of the nanoparticles increased from 10 nm to 60 nm with the increasing of ferric nitrate molar ratio. Our study reveals that the samples exhibit excellent microwave absorption properties due to the high electric resistivity and the the magnetic loss result from the natural resonance in the high-frequency.band which are significant for impedance matching and electromagnetic wave absorbing. The metal core transform from Fe3C toα-Fe and emerge a lot of onion-like carbon nanoparticles after 1000℃heat treatment. However, the reflection loss of the samples are lower than the carbon-encapsulated Fe3C nanoparticles due to the structural transformation by heat treatment. In a word, the carbon-encapsulated Fe/Fe3C nanoparticles synthesized by the modified carbonization method have a potential application in the production of microwave absorbing materials in the high-frequency. Our study provide a theoretical reference for the microwave absorption research of the metallic nanomaterial which would be a ideal candidate for electromagnetic wave absorption in the future.