Abstract: Using a sol-gel route with polyvinyl pyrrolidone as the surfactant, the carbonyl iron microparticles were uniformly and fleetly coated by SiO₂ nanoshell, whose thickness was conveniently different by changing reaction time. The influences of shell thickness on the properties of the Fe/SiO₂ core-shell particles were studied. The results show that increasing the thickness of SiO₂
nanoshell (D_shell), the anti-oxidation property of the Fe/SiO₂ core-shell
composite particles is obviously improved while microwave permittivity decreased monotoneously. The saturation magnetization shows a maximum
value while both the coercivity and remnant magnetization show minimum
values at D _shell=15nm. Meanwhile, the radar absorbing coating based on the
Fe/SiO₂ core-shell composite particles with D _shell=15nm shows a maximum
bandwidth of more than 10GHz, in which the reflective loss is less than --8dB.

Key words: core-shell particles, carbonyl iron, silica, microwave absorbing