Template free synthesis and electromagnetic wave absorption properties of monodispersed hollow magnetite nano-spheres

Abstract

Monodispersed hollow magnetite spheres with diameter of about 500 nm and a shell thickness of approximately 150 nm were synthesized through a simple solvothermal process in ethylene glycol (EG) in the presence of polyvinyl-pyrrolidone and urea for electromagnetic absorption applications. The electron microscopy images showed that the obtained magnetite spheres are composed of small particles with the size 50–100 nm and are hollow in nature. A possible formation mechanism for the hollow magnetite spheres was proposed and it was confirmed by the control experiments. The hollow magnetite spheres exhibited a high saturation magnetization value of 90.6 emu g⁻¹ and coercivity of 300 Oe at room temperature. The epoxy resin composites with 68 wt% hollow magnetite spheres provided good electromagnetic wave absorption performance (RL < −20 dB) in the range of 1.6–3.0 GHz over the absorber thickness of 5–9 mm. A minimum RL value of −42.7 dB was observed at 2.0 GHz with a thickness of 6.9 mm.