Preparation and properties of cobalt oxides coated carbon fibers as microwave-absorbing materials

Cobalt oxides/carbon fibers (CoOx/CFs) composites were synthesized by thermal oxidation of cobalt coated carbon fibers (Co/CFs). The scanning electron microscopy images and X-ray diffraction pattern indicate that the layers are about 0.7 μm and composed of Co3O4 and CoO (CoOx), the preferred condition for preparation of CoOx/CFs composites is to anneal Co/CFs precursors at 350 °C for 3 h in air. The coercivity, saturation magnetization and residual magnetization of the CoOx/CFs composites are 464.8 Oe, 10.62 emu/g and 2.21 emu/g, respectively. The reflectivity of cobalt oxides coated carbon fibers (1.11–5.12 mm in thickness) is less than −10 dB over the working frequency range of 4.04–18.00 GHz and less than −20 dB over 11.54–14.77 GHz. The lowest reflectivity is −45.16 dB at 13.41 GHz when the thickness is 1.50 mm.