Nano-scaled onion-like carbon: Prospective material for microwave coatings

Microwave absorption properties of a novel electromagnetic material - onion-like carbon (OLC) produced by annealing of detonation nanodiamonds in vacuum - have been studied in microwave frequency range. The OLC electromagnetic (EM) absorption ability can be optimized by varying the nanocarbon cluster size and nanodiamond annealing temperature so that effective EM coatings can be produced. Attenuation of EM waves in the 26-38 GHz frequency range had been studies for both OLC powder and polymer composites. For powder samples it was concluded that OLC aggregates with higher conductivity (higher annealing temperature of the precursor nanodiamond particles) and larger aggregate sizes provide higher efficiency for attenuation of the EM radiation. At the same time, when dispersed in a polymer matrix, more efficient shielding properties had been observed for OLC aggregates of the smallest sizes as compared to larger-sized aggregates at the same OLC loading. This is attributed due to the better dispersion and formation of a continuous conductive network by smaller aggregates (reaching the percolation threshold).