Preparation And Electromagnetic Wave Absorption Properties Of Different Morphology NiCo₂O₄ Crystals

The electromagnetic wave absorbing materials are of great significance to strengthening national defense forces,improving people's living environment,and safeguarding information security.Development and preparation of materials that are both"thin?light?wide?strong"and multi-frequency absorption,as well as anti-oxidation have been targets of research workers.N iCo₂O₄ has gradually been applied to the new field of wave-absorbing materials because of multiple advantages,such as good anti-oxidation and corrosion resistance,high electrical conductivity,large specific surface area,simple preparation process,and environmental friendly.We successfully prepared different micro-morphologies NiCo₂O₄ by solvothermal and calcining two-step methods.The influence of reactants?chlorate,nitrate?,reactant concentration and solvent heat temperature?90oC?120oC?150oC?180oC?on the morphology and properties of N iCo₂O₄ crystals and their precursors were studied.The mechanism of different structure of cobalt nickel oxide precursors in the solvothermal process were analyzed;and the electromagnetic properties of NiCo₂O₄ were tested.We discussed the mass ratio of N iCo₂O₄/paraffin composite,explored the primary mechanism of its electromagnetic wave absorption.The research showed:that the microstructure of NiCo₂O₄ crystal has been formed in its precursor phase.Compared to the uneven rod-shaped N iCo₂O₄synthesized by using chlorate as the reactant,the N iCo₂O₄ microstructure synthesized with nitrate was more homogeneous,and showed excellent electromagnetic wave absorption capability.The optimum mass ratio of N iCo₂O₄/paraffin composite was50:50.With nitrate as reactants,different urchin N iCo₂O₄ were successfully prepared by changing reactants concentration at 90oC.The reactants concentration was higher,the nanorods on surface were smaller.And the corresponding elec tromagnetic wave absorption capacity gradually increased and tended to be stable.The RL_min of urchin-shaped NiCo₂O₄ was-25 dB when the reactant concentration was the highest,and the effective absorption frequency band at coating thicknesses 2⁵.4 mm is 3¹8 GHz.Stepwads,hollow urchin,self-assembled sphere,and two-dimensional lamellar N iCo₂O₄ were prepared by increasing reaction temperatures to 120oC?150oC?180oC,all this exhibited good electromagnetic wave absorption capabilities.The hollow urchin-shaped N iCo₂O₄ optimal value of RL_min is-42.23 dB at 4 GHz for the thickness of 4.8 mm,and the bandwidth of the RL<-10 dB could achieve 15 GHz?3¹8 GHz?at coating thicknesses 2⁵ mm.The self-assembled sphere N iCo2O4optimal value of RL_min is-45.5 d B for the thickness of 4.2 mm.The two-dimensional layer NiCo₂O₄ optimal value of RL_min is-34 dB at 4 GHz for the thickness of 5.3 mm.The change of the solvothermal conditions affected the crystallization and the crystallinity of the precursors,which leaded to the formation of N iCo₂O₄ with different microstructures.And the microcosmic morphology of N iCo₂O₄ had a huge influence on the microwave absorbing properties.The geometric effect caused by urchin-shaped surface nanorods"quasi-antenna",hollow,sheet-like and self-assembled spheres cross-sheet structure had a very big contribution to the electromagnetic absorption of N iCo₂O₄,except for the interfacial polarization,relaxation polarization and resonance phenomenon.