Preparation And Properties Of Microwave Absorbing Materials Based On Chaff And Cotton Fiber

With the rapid development of electronic technology,microwave absorbing materials has been widely used in civil and military fields.Traditional absorbing materials have great limitations in practical application due to their complex synthetic processes,high cost,non-renewable raw materials,non-recyclability and degradation when they reach the end of their useful life.Therefore,it is particularly important to develop a high-application value absorbing material with simple process,low cost,excellent absorbing performance,and environmental considerations.Compared with traditional absorbing materials,chaff,cotton fibers and other biological materials have the advantages of rich natural microstructures,wide sources,low prices,and degradable regeneration,so they have become one of the effective carbon sources of new biomass microwave absorbing functional materials.In this paper,Ni_xMn_1-xFe₂O₄/carbonized chaff(x=0.3,0.5,0.7)and Ni_0.3Mn_0.7Fe₂O₄/carbonized cotton fiber composites were prepared by co-carbonization method and solvent heat method,and the effects of carbonization atmosphere,carbonization temperature,Ni²⁺/Mn²⁺mole ratio and biomass filling content on the electromagnetic parameters,absorbing performance and absorbing mechanism of the composites were studied.The results are as follows:(1)A series of Ni_xMn_1-xFe₂O₄/carbonized chaff(x=0.3,0.5,0.7)composites have obvious paramagnetic properties.The carbonization of chaff under nitrogen atmosphere has less degree of oxidation in organic matter,and the stacked pore structure of chaff remains relatively complete.Here,the carbonized chaff filling content and Ni²⁺/Mn²⁺mole ratio make the complex permittivity,complex permeability and reflection loss of the composite material change regularly.Compared with pure Ni_0.5Mn_0.5Fe₂O₄nanoparticles,N_i0.3Mn_0.7Fe₂O₄/Carbonized Chaff-N₂with 10 wt%percentage of nitrogen atmosphere carbonized chaff possesses good impedance matching,strong natural resonance,advisable Debye dipole relaxation and coordination laminated structure effect etc.within the range of0.1-3.0 GHz.Hence,the best reflection loss of composite is-14.58 d B at 1.91 GHz,and the RL value below-10 d B absorption band is 1.46-2.41 GHz(0.95 GHz)at the thicknesses of 4mm.(2)The carbonization temperature affects the diameter and surface structure of the cotton fiber when it is carbonized in nitrogen atmosphere.The surface of carbonized cotton fiber at 700?has a uniform and dense folded microstructure,and the combination with Ni_0.3Mn_0.7Fe₂O₄is conducive to the dispersion of magnetic nanoparticles and the multiple reflection attenuation of electromagnetic wave.With the increase of carbonized cotton fiber content from 0 wt%to 15 wt%,the imaginary part value of complex dielectric derivative increased from 0.58 to 6.58,and the imaginary part of complex permeability increased from 1.01 to 59.38.Taking into account the difficulty of mixing with paraffin,the composite filled with 10 wt%carbonized cotton fiber has the best absorbing effect when the coating thickness is 5 mm,and its RL value is up to-51.12 d B at 0.56 GHz,and the effective range is between 0.33 and 0.91 GHz.