The Study On Microwave Absorbing Performances Of Sea Urchin-like NiCo₂O₄ Matrix Composites

Electromagnetic wave radiation can be seen everywhere in our lives,and the research and performance improvement of absorbing materials is of great significance.The research status of electromagnetic wave absorbing materials shows that the composition,morphology and structure of the material largely determine the intrinsic electromagnetic characteristics of the material.The rich interface and shape anisotropy of NiCo₂O₄ materials are conducive to the attenuation of electromagnetic waves.Therefore,we study the morphology control of NiCo₂O₄ and construct NiCo₂O₄-based nanocomposites to obtain absorbing materials with excellent absorbing properties.Firstly,NiCo₂O₄ was synthesized by hydrothermal method.With different morphologies,NiCo₂O₄ were prepared by controlling the initial concentration of reactants.The effects of morphologies on electromagnetic parameters and absorbing properties were studied.The experimental results showed that A4 had the best absorbing property,and its sample had the lowest RL-21.97 dB,when the thickness was 1.6 mm,and the absorption frequency bandwidth reached 5.78 GHz（12.22-18GHz）.Then C/NiCo₂O₄ composites were synthesized by hydrothermal method to study the effect of different carbon content on the absorbing properties of the samples.Among them,C2 had the best absorbing performance,and its sample had the lowest RL-43.54 dB,when the thickness was 1.5 mm,and the frequency was 14.31 GHz.Compared with pure NiCo₂O₄,the absorbing property was greatly improved.After that,the urchin-like NiCo₂O₄ was coated with ZnO by sol-gel method to prepare NiCo₂O₄/ZnO composites,and the absorbing properties of NiCo₂O₄/ZnO composites with different mole ratios were studied.The morphologies of all the synthesized samples keeped the original sea urchin shape.Through the study of the absorbing properties of NiCo₂O₄/ZnO composites,the dielectric constant decreased with the increase of the proportion of ZnO in the frequency range of 2-18 GHz,and when the molar ratio of NiCo₂O₄ to ZnO is 1:4,it had the best wave absorbing performance.The sample had a minimum RL of-43.05 dB and the absorption frequency bandwidth reached 3.75 GHz（8.65-12.40 GHz）at a thickness of 2.6mm,and a frequency of10.12 GHz,.This is due to the introduction of ZnO,which improved the impedance matching and attenuation ability of the samples.Finally,based on the excellent absorbing properties of C/NiCo₂O₄ and NiCo₂O₄/ZnO composites,hierarchical urchin-like C/NiCo₂O₄/ZnO composites were successfully prepared by hydrothermal method and subsequent sol-gel method,and studied its absorbing performance.The minimum RL value of C/NiCo₂O₄/ZnO composite material can reached-43.61 dB at 11.61 GHz,the thickness is only 2.4 mm,and the absorption frequency bandwidth RL≤-10 dB is 4.32 GHz.The improvement of absorbing performance is related to good impedance matching,unique structure and interfacial polarization caused by the synergy between multiple components.