Microwave electromagnetic property of SiO2-coated carbonyl iron particles with higher oxidation resistance

Flake carbonyl iron (CI) particles and amorphous silica were used to fabricate SiO₂-coated CI particles through the Stober process. The as-prepared SiO₂-coated CI particles were annealed at 500 °C for 1 h under argon and air atmosphere. The XRD results showed that only a little amount of oxides were formed when the SiO₂-coated CI particles were annealed under the air atmosphere. The magnetic properties of the SiO₂-coated CI particles before and after annealing treatment showed little change, indicating that amorphous silica appears to be very effective in reducing oxidation of the CI particles. The reflection loss exceeding −10 dB can be obtained in the frequency range of 9.9-14.6 GHz and a minimum value can be reached to −21.5 dB at 12.2 GHz for the annealed SiO₂-coated CI particles with the composite thickness being 1.5 mm. The mechanism of annealing treatment influence on the electromagnetic properties and microwave absorption of the SiO₂-coated CI particles was also discussed.