Structure and electromagnetic properties of both regular and defective onion-like carbon nanoparticles

Both regular and defective onion-like carbon (OLC) nanoparticles were prepared by the arc-discharge process using hexane (C6H14) and ethanol (C2H5OH) as carbon sources. The formation of defective sites in OLC nanoparticles is ascribed to the introduction of oxygen of ethanol. It is shown that high vacuum or using raw materials without oxygen is favorable to form regular onion-like microstructure. For defective OLC/paraffin composites, the valuable microwave-absorption areas (<-10 dB) increase with the weight fraction increasing from 20% to 50%. The further increasing of concentration (60%) will decrease greatly the microwave absorption due to the strong reflection of incident microwave induced by the high conductivity of system. The reflection loss (RL) exceeding -10 dB can be obtained for 50% defective OLC/paraffin composites in the thickness range of 1.4-3.4 mm. The large amounts of defective sites are responsible for the excellent microwave-absorption performances of defective OLC/paraffin composites. (C) 2015 Elsevier Ltd. All rights reserved.