Impact of Al2O3, TiO2, ZnO and BaTiO3 on the microwave absorption properties of exfoliated graphite/epoxy composites at X-band frequencies

Bi-filler composites composed of exfoliated graphite (EG) and any one of Al2O3, BaTiO3, ZnO and TiO2 metallic oxides are fabricated in epoxy matrix to improve microwave absorption properties exclusively in X band. These composites are characterized for their morphology and compositional studies using SEM, Raman spectroscopy and X-rays photoelectron spectroscopy. The strong reflection loss values of −43 dB (99.995% absorption), −25.7 dB (99.731% absorption), −33.9 dB (99.959% absorption) and −46.0 (99.997% absorption) with wide effective bandwidths are successfully achieved by the EG/epoxy composites containing 40 wt% Al2O3, 30 wt% BaTiO3, 30 wt% TiO2 and 20 wt% ZnO when the thicknesses are 1.8, 1.6, 1.4 and 1.8 mm, respectively. These absorption performances are attributed to the perfect matching conditions, multiple internal reflections, interface polarizations and defect polarizations. The incorporation of metallic oxides demonstrated improved adhesion and reinforcement efficiency factors, as well as uplifted the values of flexural strength and thermal conductivity of EG/epoxy composites. These properties justifies the potential future of metallic oxide/EG/epoxy composite in microwave absorption applications.