Secondary Granulation Of Fe And C Nanoparticles By Spray Drying Method And Microwave Absorbing Properties

New nano-absorbing materials have special properties due to the nanometer size effect compared with the macroscopic counterpart. Nanometer absorbing material provides a new direction providing thin coating, high absorption and wide absorption band. However, the nanoparticles agglomerate easily, thus the dispersion and stability of the nanoparticles is poor. In this study, the spray granulation method was extended to prepare micro-sized electromagnetic absorption particles with nano-wave absorbing materials. Micron particles were stable and easy for storage, which solved part of problems faced by the nano-absorbing materials.In our research, Fe nanoparticles and C nanoparticles (Super-p) were used as electromagnetic wave absorbing material and polyvinyl alcohol (PVA) was used as matrix. The Fe nanoparticles was modified by KH550 due to the poor dispersion stability. In addition, the infrared spectra of modified Fe nanoparticles and C nanoparticles were analyzed. The results showed an obvious improvement for the modified Fe nanoparticles dispersed stability, and the C nanoparticles had good dispersion in PVA solution because of the organic surface structure.The Fe nanoparticles were prepared by arc discharge plasma, and was used as magnetic loss material, while C nanoparticles was used as dielectric loss material. The Fe/PVA composite absorbing material and Fe/C/PVA composite absorbing material were prepared by spray granulation method and the absorbing performance was studied also. In the Fe/PVA composite particles with the mass fraction increment of Fe nanoparticle, the dipole polarization, the space-charge polarization and the interfacial polarization were enhanced. The dielectric constant and dielectric loss factor were also enhanced, thus the wave absorbing properties were improved. The Fe/PVA composite particles has excellent performance in high frequency for thick layers, when the mass fraction of Fe nanoparticles was 90%, the minimum reflection loss was -24.9 dB at 12.6 GHz, with a corresponding large thickness of 8.4 mm. In the Fe/C/PVA composite particles, the radio of magnetic loss material Fe nanoparticles and dielectric loss materials C nanoparticles could be controlled, which helped to regulate the impedance matching. In our case, when the content ratio of the C nanoparticle, the modified Fe nanoparticle, and the PVA was 21:49:30, a minimum reflection loss of -42.7 dB at 3.7 GHz was obtained, for a composite with 4.6 mm in thickness.