The effect of temperature on structure and permittivity of carbon microspheres as efficient absorbent prepared by facile and large-scale method

Based on the concept of environment-friendly development strategy, green preparation method is crucial. Therefore, starch-derived micron solid carbon spheres (SCs) were fabricated via spray-drying followed by carbonization processing, in which is no any harmful substances in whole process. Through tuning the carbonization temperature, SCs with a moderate degree of graphitization and intrinsic defects can be obtained. The microstructure, permittivity and microwave absorption of SCs were studied. Results show that the SCs with a larger number of micropores is composed of nanocrystalline regions and amorphous areas. The paraffin-based composites with 25 wt% SCs carbonized at 800 °C displays a strong microwave loss feature, the minimum reflection loss of −64.8 dB at 9.02 GHz with thickness of 2.57 mm. Meanwhile, the effective absorption band (<-10 dB) can reach 3.1 GHz with the thickness of 2.22 mm, covering 78% of X-band, which because of its good impedance matching and dielectric loss ability resulted from the synergistic effect between the microstructure and graphitization. This work offers a facile, larger-scale and environmental-friendly method for the preparation of micron carbon-based absorbents that can serves as an alternative to nano-scale absorbents to overcome the poor dispersion of nanoparticle in the matrix.