Gas-Phase Detonation Synthesis of Defect-Rich Nanographitic Carbon for Lightweight Microwave Absorption

Abstract

Scalable preparation of lightweight dielectric absorbers is critical for electromagnetic-interference mitigation; however, many high-performance carbon absorbers require multistep syntheses or high filler loadings that compromise processability and impedance matching. Here, defect-rich nanographitic carbon (D-NGC) is synthesized directly from acetylene/oxygen mixtures by gas-phase detonation, in which the transient high-temperature/high-pressure and rapid-cooling environment drives the formation of curled, wrinkled nanographitic domains with abundant defects and heterogeneous interfaces. When dispersed in paraffin at only 9.09 wt %, D-NGC delivers a minimum reflection loss (RL) of –67.34 dB at 10.12 GHz and an effective absorption bandwidth (EAB, RL ≤–10 dB) of 4.03 GHz at a thickness of 3.01 mm while maintaining a low apparent density of 0.89 g cm–3. When the thickness is reduced to 2.20 mm, the EAB expands to 5.37 GHz, and the absorption peak is located at 14.42 GHz. Cole–Cole analysis and Kramers–Kronig-consistent distributed relaxation fitting reveal that defect- and interface-associated polarization relaxation dominates dielectric loss in the X/Ku bands, whereas effective conduction loss is mainly confined to low frequencies. Interfacial-reflection and perfect-matching analyses further clarify that high absorption arises from the combined optimization of moderate complex permittivity, attenuation, and impedance matching rather than from maximizing dielectric loss alone. These results identify gas-phase detonation as a rapid, potentially scalable route to defect-engineered nanocarbons and provide a quantitative framework for designing lightweight carbon-based microwave absorbers.