The Synthesis And Electromagnetic Absorption Performance Of Nanometer Silicon Dioxide?Carborundum?zinc Ferrite@carbon Composite

With the rapid development of electronic technique,absorbing material is not only used in aircraft and ships,but also used in all kinds of electronic products,such as:Stealth aircraft?stealth ships.computers?TV?stereos,etc.The application range of electromagnetic energy is constantly expanding,which brings about various electromagnetic pollution,influencing human health seriously.The absorbing materials of single function can not meet the needs of social development,and the new nano-composite materials with strong absorption,broadband,light and high temperature are developing rapidly.In addition,worldwide scientists are working on designing and preparing a variety of nano-composite materials to deal with serious electromagnetic pollution.Among them,the hollow structure of the nano-composite materials because of the existence of the cavity,make its have some unique performance.The electromagnetic wave of incidenting to the hollow structure can occur constant reflection and refraction in the internal cavity,thus the catches of incident electromagnetic wave are greatly enhanced,and the electromagnetic wave absorption performance of materials are further improved.As a new type of absorbing material,nanometer SiC not only possess many unique properties such as quantum size effect,small size and interface effects,but there are also high temperature resistant,high strength,large resistivity and weakening infrared signal,is a kind of very considerable absorbing material.Ferrite because of possessing both ferrous magnetic and dielectric properties,can make the incident electromagnetic wave producing magnetic hysteresis loss and dielectric loss,which is widely used in electromagnetic absorption and shielding and also the more mature absorbing materials researched,but the application of zinc ferrite in electromagnetic wave absorption is rare.On the other hand,carbon materials with high dielectric loss tangent and modified easily,when composited with other materials,depending on electronic polarization or interface of the medium to attenuation electromagnetic wave,is an ideal absorbing additive.Based on this topic,the research contents of this paper are as follows:(1)The SiO2 microspheres as the template,coating a layer of carbon on the surface of SiO2 by hydrothermal method,geting SiO2@C composites(S-i,i = 1,2,3,4),by changing the size of SiO2 microspheres and the thickness of carbon layer to regulate its electromagnetic wave absorption performance.It is found that the performance of S-2 sample is the best,when the coating thickness is 4.9 mm,the minimum reflection loss reaches-37.7 dB at 4.25 GHz.The study of absorbing mechanism shows that the conductive loss of carbon layer,interface loss and interface polarization between the silicon layer and the carbon layer make the electromagnetic wave absorbing performance significantly better than other composites.(2)The SiO2@C composites obtained in(1)are treated with high temperature under Ar protection so that SiO2 and C can react and generate SiC,and hollow SiC@C can be obtained by etching the rest of SiO2.The electromagnetic wave absorbing pr,operties of the composites are controlled by changing the size of cavity.Considering the minimum reflection loss?effective bandwidth and the thickness of materials,the minimum reflection loss of SC-2 sample is-39.2 dB at 1.5 mm and 16.4 GHz,effective bandwidth(?-10 dB)up to 6.0 GHz(12?18 GHz).The excellent absorbing performance is mainly attributed to the conduction loss of carbon black,silicon carbide dielectric loss as well as the polarization between the two interfaces,and the hollow structure is also beneficial to improve absorbing properties of composites.(3)The hierarchical core-shell structured ZnFe2O4@SiO2@C composites are designed and prepared by the method of layered coating,then the yolk-shell structure ZnFe2O4@C composites(YS-ZF@C)can be obtained after selective etching SiO2.And by changing the amount of TEOS,the thickness of SiO2 and the cavity size of composites can be easily adjusted.Among them,the Y-2 sample with a cavity size of about 60 nm has the minimum reflection loss,and its minimum reflection loss at 16.2 GHz is up to 37.1 dB,and the effective absorber bandwidth(<-10 dB)is about 4 GHz.