High permittivity and microwave absorption of porous graphitic carbons encapsulating Fe nanoparticles

Abstract

Porous graphitic carbons encapsulating Fe nanoparticles (PGCFs) were fabricated by infiltrating activated carbon (AC) with an iron salt and thereafter heat-treating the products in vacuum, and the electromagnetic parameters of the PGCF were investigated over 2–18 GHz frequency. The results demonstrated that the formation of porous graphitic network encapsulating Fe nanoparticles endowed the composite a very high permittivity and dielectric loss at 2–18 GHz. Return loss (RL) for the PGCF-based absorbers were investigated based on the measured electromagnetic parameters. A typical dual-layer absorber exhibited an excellent microwave absorption with a 43 dB maximum absorption at 10 GHz and a nearly 7 GHz bandwidth for RL < −20 dB.

Introduction

It is increasingly important to design and fabricate electromagnetic absorbers to resolve electromagnetic interference (EMI) aroused by substantive applications of electrical and electronic equipments and devices [1], [2], [3], [4]. According to absorption mechanisms, electromagnetic absorbers can be divided into dielectric absorbers and magnetic absorbers [5]. In order to achieve an excellent absorption, considerable attention has been devoted in recent years to the development of composites consisting of both dielectric and magnetic fillers, which are expected to have a coupled effect on dissipation of microwave energy [6], [7]. Among a variety of dielectric fillers, nanocarbons such as carbon nanotubes and carbon nanofibers, have attracted great attention recently because of their advantages in light-weight, large aspect ratio, good conductivity, thermal and chemical stability [8], [9], [10]. In general, these nanocarbons and magnetic fillers, are incorporated into a polymer matrix in two ways; one is directly mixing nanocarbons and magnetic fillers in a polymer solution [11], and the other is encapsulating magnetic fillers into nanocarbons and then dispersing the mixture into a polymer [12]. However, a common problem regarding the two compounding processes is the difficulty in uniformly dispersing these nanomaterials into a polymer matrix with a high viscosity, which hiders the large-scale application of nanocarbons for microwave absorptive materials.

In this paper, a simple but effective method is proposed to in situ grow Fe/C nanostructures within a porous amorphous carbon matrix to fabricate porous graphitic carbons encapsulating Fe nanoparticles (PGCFs) for microwave absorption application. The in situ formed nanostructures could be Fe encapsulated graphitic capsules or Fe/C conductive networks, which are closely dependent on the sintering temperature. Thus, the method circumvents the difficulty of the dispersion of nanoscale electrical and magnetic fillers, suggesting much lower fabrication cost and better reproducibility.