Synthesis and Microwave Absorption Performance of Fe₃O₄/Graphene Nanoplatelet/Carbonized Rice Husk Nanocomposite Epoxy Coatings on Aluminum Substrates for X-Band Radar Absorption

In this study, an Fe₃O₄/graphene nanoplatelet/carbonized rice husk (Fe₃O₄/GNPs/CRH) nanocomposite was synthesized via in situ co-precipitation and used as an epoxy coating on an aluminum substrate. The CHR was prepared by carbonization of rice husk at 800°C for 2 h under a continuous N₂ atmosphere. The FTIR instrument was used to identify the characteristic functional groups of Fe₃O₄, GNPs, CRH, and the resulting nanocomposite. The coating thickness and surface wettability were evaluated through cross-sectional thickness measurements and water contact angle measurements, respectively. Microwave absorption performance was evaluated using a vector network analyzer (VNA) in the X-band frequency range of 8–12 GHz. The Fe₃O₄/GNPs/CRH nanocomposite exhibited a maximum reflection loss (RL) of −31.88 dB at 8.60 GHz with a thickness of 3 mm and a through power of 99.93%, whereas Fe₃O₄, GNPs, and CRH exhibited maximum RL values of −23.56, −23.95, and −24.75 dB, respectively. For the epoxy coating on aluminum, the thickness increased from 0.311 to 2.066 mm as the number of coating cycles increased. The microwave absorption performance improved with increasing coating thickness, reaching a maximum RL of −27.92 dB at 8.68 GHz for a coating thickness of 2.066 mm, with a through power of 99.83%. Water contact angle measurements showed hydrophilic behavior for all coated samples, with contact angles ranging from 51.43° to 59.49°, compared with 75.38° for uncoated aluminum