Preparation And Microwave Absorbing Properties Of Ferrite-LAS Based Glass-ceramic Composites

With the rapid development of electronic equipment and communication technology,the danger of electromagnetic radiation is becoming increasingly serious,so the prevention and control of electromagnetic interference is particularly important for human health and information security.For a long time,the development of microwave absorbing materials with strong absorption,wide bandwith,thin thickness and light weight has long been considered the best solution to this problem.The ideal microwave absorbing material needs to have strong attenuation capability and good impedance matching,among which,ferrite receives wide attention in the field of wave absorption due to its low cost,simple preparation,good ferromagnetie and dielectric properties.NiFe2O4,as a soft magnetic material with high saturation magnetisation strength and curie temperature,good cocrcivity and dielectric properties,is a popular microwave absorbing material.However,it is difficult to meet the requirements of low weight,good impedance matching and high microwave absorption power with a single absorbing material,so the preparation of composite absorbing materials has become the focus of research.Lithium aluminum silicate(LAS,Li2O-Al2O3-SiO2)glass-ceramics are effective in optimizing the impedance matching of absorbing materials due to their low dielectric constants.In addition,Ni3Fe has a high dielectric constant and magnetic permeability.Two-dimensional Ti3C2Tx has high electrical conductivity,abundant surface functional groups and intrinsic defects,as well as easy processing of the structure.They can all be effective in improving electromagnetic wave attenuation.In addition to optimizing the composition of wave absorbing materials,the construction of special microstructures is one of the effective measures to improve the absorbing properties of materials.Based on both enhanced attenuation characteristics and improved impedance matching,this paper adopts the traditional mature magnetic NiFe2O4 wave absorbing material as one of the phases,lithium aluminum silicate(LAS)to adjust the dielectric constant and impedance matching of the material,and subsequently introduces high dielectric loss Ni3Fe and Ti3C2Tx,respectively,and prepares a series of composite materials with excellent microwave absorption performance by constructing special microstructures.The effect law of each phase composition and process on the wave absorption performance was systematically studied,and the wave absorption mechanism was revealed.The results show that:(1)Based on the Li2FO-Al2O3-SiO2-Fe2O3-NiO multifunctional system,LiFe5O8 and NiFe2O4 magnetic absorbing phases were precipitated in LAS-based glasses by high-temperature melting combined with heat treatment precrystallization,and a new type of LAS-based glass-ceramics with thin thickness,strong absorption and wide frequency band for microwave absorption was successfully prepared.Limited by the viscosity of the glass melt,19.2 wt%of Fe2O3 and 9 wt%of NiO were the maximum additions that successfully formed the glass matrix,and the glass of this composition had the best absorption performance after precrystallisation treatment at 800℃,with an RL value of-48.2 dB at a thickness of 2.0 mm,achieving an effective absorption width of 4.4 GHz,and an effective absorption width of 6.72 GHz at 2.6 mm.The excellent microwave absorption performance is due to the interfacial polarization between the LiFe5O8,NiFe2O4,LiAlSi2O6 and amorphous phases,and the intrinsic dielectric and magnetic losses of the ferrite and the good impedance matching.(2)Based on the idea of constructing the ferrite-alloy-glass multiphase heterogeneous microstructure,core-shell-like NiFe2O4/Ni3Fe/LAS nanocomposites has been successfully prepared by using sol-gel,hydrothermal and in situ reduction methods.In which,NiFe2O4 and Ni3Fe provide strong magnetic and dielectric losses,while the introduction of the LAS glass wave-transparent phase modulates the complex dielectric constant,and effectively improving impedance matching.The multi-component nature of NiFe2O4/Ni3Fe/LAS produces abundant heterogeneous interfaces,and the strong interfacial polarization contributes to the attenuation of electromagnetic waves.Compared to NiFe2O4 and NiFe2O4/Ni3Fe,the core-shell-like NiFe2O4/Ni3Fe/LAS nanopowders have excellent wave absorption properties.At the thickness of 2.3 mm,the RL of NiFe2O4/Ni3Fe/LAS reaches-50.7 dB at 11.36 GHz with an effective absorption bandwidth(EAB)of 5.04 GHz,while at 2.0 mm the EAB is up to 7 GHz.(3)The surface modification of NiFe2O4@LAS nanoparticles was carried out using CTAB to make them positively charged.After electrostatic adsorption,they were uniformly loaded on the Ti3C2Tx surface,while alkaline flocculation led to the transformation of 2D Ti3C2Tx nanosheets into 3D interconnected porous folded structures.Electromagnetic parameters show that NiFe2O4@LAS can effectively improve the impedance matching and magnetic loss of Ti3C2Tx.The magnetic-dielectric synergy,optimized impedance matching,interfacial polarization and multiple reflection of electromagnetic waves gives the composite an improved and excellent wave absorption performance.The reflection loss for NiFe2O4@LAS additions of 20 wt%,25 wt%and 30 wt%were all better than that of pure Ti3C2Tx.The best absorption performance was achieved with NiFe2O4@LAS added at 20%,with an RL of-47.6 GHz at 1.6 mm and 14.24 GHz,corresponding to an effective absorption width of 5.28 GHz(12.72-18 GHz),the effective absorption width is 5.44 GHz(12.56-18 GHz)at 1.65 mm.