Microstructure and Millimeter-wave Attenuation Performance of Exfoliated Graphite with Different Expanding Volume

Exfoliated graphite with different expanding volume (EV) was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid, and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. Its microstructure was analyzed by scanning electron microscope, and its millimeter-wave attenuation performance was measured by a static method. The results show that the exfoliated graphite forms more microcellular structures and its layers become thinner with the increasing of EV, the interlayers are fully opened and there are more tiny graphite flakes with size distribution between several microns and several ten microns. The millimeter-wave attenuation performance enhances with the increasing of EV, and the 3mm wave attenuation value rises from 5.7dB to 8.68dB When EV increases from 233ml/g to 450ml/g, which is mainly attributed to the full expansion of exfoliated graphite to form larger scattering cross section and the absorption of more tiny graphite flakes with size distribution between several microns and several ten microns.