Comparison of the microwave absorption performance of core-shell SiO₂@C and hollow carbon nanospheres with different sizes

Core-shell structured SiO2@C nanospheres with different sizes were fabricated using a method of "template synthesis - organic coating - carbonizing". After etching away the SiO2 cores, hollow carbon (void@C) nanospheres were obtained. The microwave absorption properties of the different structured nanospheres were compared, and the size effect of the nanospheres was further discussed. The SiO2@C/paraffin composites with a filling ratio of 30 wt% achieved a broad effective absorption (reflection loss <=-10 dB) of 7.4 GHz at a thickness of 3.2 mm, covering the whole X and Ku bands, and the minimum reflection loss reaches -41.7 dB at 17.6 GHz at a thickness of 2.6 mm. The void@C/paraffin composites achieved an effective absorption broadband of 7.1 GHz and a minimum reflection loss of -21.9 dB at a thickness of 2.2 mm and a low filling ratio of 2 wt%, meeting the requirements for industrial lighting applications. Moreover, for both structures, the nanospheres with larger diameters exhibited stronger absorption performance. The excellent EMW absorption performances of the core-shell SiO2@C/paraffin and void@C/paraffin composites are mainly due to polarization loss and electrical conductivity loss, respectively, depending on the mobility of the electrons in the materials.