Preparation And Electromagnetic Wave Absorption Properties Of Mn And Cu-based Semiconductor Nanocomposites

Electromagnetic interference and radiation caused by the wide application of various large electronic equipment and the development of communication equipment are increasingly serious.Electromagnetic wave absorption(EMA)materials can convert electromagnetic energy into heat energy and dissipate it,which is an effective method to solve electromagnetic pollution.In addition,as the material basis of stealth technology in military field,EMA materials also play important role in the detection of counter reconnaissance system.Therefore,it is of great significance to explore lightweight and efficient EMA materials.Compared with traditional magnetic materials,semiconductors are characterized by low cost,easy preparation,small permittivity,moderate conductivity and good stability.Furthermore,they can also produce dielectric loss.So semiconductors are gradually applied to the EMA field.However,the single semiconductor dielectric material is also limited by the insufficient attenuation ability and the poor impedance matching.To solve the above problems,MnO and Cu19S5 semiconductor materials are combined with magnetic materials or carbon to construct composite absorbers.By adjusting the component content of the composites,the electromagnetic parameters are further controlled,and thus the impedance matching and attenuation ability are optimized.Finally,the absorption strength,absorption bandwidth and matching thickness of the semiconductor composites are improved.Additionally,the electromagnetic wave loss mechanism is discussed in depth.The main contents are as follows:(1)Three-dimensional(3D)porous MnO/Co composites were prepared by hydrogen reduction of MnCo bimetallic oxides.This method achieves the uniform combination of nano-sized dielectric material MnO and magnetic Co particles.The introduction of magnetic Co particles significantly improves the attenuation ability of the composites.The existence of MnO particles inhibites the excessive permittivity of pure Co,thus improving the impedance matching of the composites.By adjusting the relative content of the two components,the effect of dielectric MnO and magnetic Co on the electromagnetic parameters and EMA performance is discussed.The obtained 3D porous MnO/Co composites exhibites significantly improved EMA performance comparing with single MnO and Co materials.The optimal reflection loss(RLmin)value reaches-64.2 dB at 10.9 GHz with the thickness of 2.3 mm,and the effective absorption bandwidth(EAB)is up to 6.0 GHz at 2.1 mm.The synergistic effect of MnO and magnetic Co particles effectively promotes the loss of electromagnetic wave(2)Considering the strong conductive loss,light weight and easy preparation of carbon materials,one-dimensional(1D)MnO@N-doped carbon composites were prepared by thermal decomposition of pyrrole on the surface of MnO2 nanotubes.By controlling the dosage of pyrrole,the thickness and content of carbon layer was adjusted.With the increase of carbon content,the conductivity of the composites increases significantly,leading to the enhancement of conductive loss.Moreo-ver,carbon coating also brings more polarization loss,which further improves the overall attenuation capacity of the composites.The MnO@N-doped carbon composites show the best EMA performance when the carbon content is 30.2 wt.%.The RLmin reaches-62.8 dB at 2.4 mm(13.3 GHz),and the EAB is 5.4 GHz at 2.5 mm.Electromagnetic simulation results show that the formation of core-shell structure is conducive to the aggregation of charge at the interface,which promotes the generation of more interface polarization.In this study,the effect of high conductive loss carbon on the dielectric loss ability of MnO is discussed,and a reasonable explanation for the polarization behavior is proposed,which provided ideas for the preparation of light-weight core-shell EMA materials.(3)The formation of heterogeneous structure is conducive to the generation of interfacial polarization.And the combination of magnetic and dielectric loss materials can effectively balance the permeability and permittivity,and thus achieving good impedance matching.Based on the above two studies,3D flower-like MnO/Co@C composites were prepared through the reduction of MnCo bimetallic oxides with pyrrole carbon.The introduction of Co with high magnetic loss,carbon layer with high conductive loss,and the formation of multiple heterogeneous interfaces endow the composites with high magnetic loss and dielectric loss ability simultaneously.By controlling the ratio of Co to MnO,the electromagnetic parameters are further adjusted,and the impedance matching is optimized.Under the synergistic effect of magnetic Co,dielectric MnO and carbon,the composites obtain strong absorption in a wide frequency range and achieves excellent low-frequency absorption performance.The optimal absorption intensity is less than-20 dB in the frequency range of 4-12 GHz.The RLmin reaches-55.3 dB at the thickness of 2.4 mm.The effective bandwidth reaches 4.6 GHz at 2.6mm,covering the whole X band(4)The preparation of metal sulfide/carbon composites by metal organic frameworks(MOFs)derivatives provides a new possibility for the construction of efficient EMA materials.In this study,the octahedral Cu9S5/C composites were prepared through carbonization and sulfidation treatment of HKUST-1.The composites are assembled with Cu9S5 nanoparticles uniformly embedding on the surface and inside of the octahedral carbon skeleton.Electromagnetic parameter tests show that both Cu9S5 and carbon can provide conductive loss and polarization loss.The electric field simulation results show that the integration of the two components provides more sites for interface polarization.By controlling the relative content of Cu9S5 antd carbon,the balance between impedance matching and attenuation ability is realized.The high loss ability enables the Cu9S5/C composites to obtain excellent absorption performance at low filling content of 45 wt.%.The Cu9S5/C composites achieve the RLmin of-62.3 dB at a thin thickness(1.3 mm),and a broad EAB of 4.7 GHz at 1.6 mm.The RLmin is less than-20 dB in a wide frequency range of 3.5?18 GHz.This experiment provides an idea for the preparation of sulfide/carbon composite EMA materials by MOFs derivatization.