Abstract
? 2022Core-shell composites Fe-N @ SiO2 with 500 nm average sizes of cores have been successfully prepared by a combination of hydrothermal, gaseous nitriding and St?ber methods. The Fe-N cores are composed of Fe4N as major phase and FeN as minority. The thickness of SiO2 shell increases continuously with increase of the tetraethyl orthosilicate weight. Relative to the natures of Fe-N, Fe-N @ SiO2 composites show slightly weaker ferromagnetic capacity, but much higher oxidation resistance. The Fe-N sample exhibits extremely high relative permittivity. With filling loading of 50 wt%, it has a moderate microwave absorption performance with a maximum reflection loss about ?10 dB. Owing to low conductivity, non-magnetic property and superior anti-oxidation ability of the SiO2 shell, the core-shell structures have considerably degraded permittivity, and nearly unchanged permeability. These changes bring a much better impedance matching between the permittivity and permeability, and further bring a greatly enhanced microwave absorption performance. All of the Fe-N @ SiO2 composites have strong absorption abilities. They are quite stable with variation of shell thickness. The composite of 52 nm shell thickness has maximum reflection loss of ?23.1 dB at 17.2 GHz, and effective absorption bandwidth (<?10 dB) of 2.4 GHz with absorber thickness 5.5 mm. The present study gives an insight on the roles of silica material influencing the iron-based absorber's absorption ability.
NSTL