Preparation and microwave absorption properties of porous charcoal/ Fe₃O₄ composites

In order to improve the shortages of big density and narrow absorption bandwidth of Fe₃O₄ absorbing material, in this study, wood-based porous charcoal (WPC)/Fe₃O₄ composites were prepared from fast-growing masson pine wood by delignification and high temperature in-situ growth methods. The microwave absorption properties of the composites were regulated by tailoring the carbonization temperature. The results of micromorphology, structure and electromagnetic parameters show that, the WPC/Fe₃O₄ composites retain the natural three-dimensional porous structure of wood with Fe₃O₄ particles evenly loaded in the carbon walls and channels of WPC. The increment of carbonization temperature (630-690℃) can enhance the electric conductivity and microwave attenuation capacity of the composites, but too high temperature causes the impedance mismatching. The composite prepared at 670℃ exhibits excellent microwave absorption performance with a minimum reflection loss of −49.5 dB and an effective absorption bandwidth of 6.24 GHz (9.04-15.28 GHz), due to its strong attenuation capability and good impedance matching characteristics. The main dissipation mechanism includes conductive loss, polarization relaxation, and synergistic effect of dielectric and magnetic loss. The strong reflection loss and wide effective absorption bandwidth of WPC/Fe₃O₄ composite suggest a good prospect in electromagnetic absorption field, which can promote the value-added and functional application of fast-growing wood.