The Application Of Porous Ceramisite Coated With Barium Ferrite In The Electromagnetic Wave Absorbing Concrete

Recently,with the rapid development and application of electronic science and technology,the electromagnetic radiation becoming more and more serious,which was produced by electronic equipment and instrument when they working.The electromagnetic radiation has been a seriously threat to people's health,equipment operation and has led to electromagnetic information leakage which has a significant impact on the security of political,economics and military.Thus,the study on cement-based composite materials with microwave absorbing properties has the important significance in defense,civil building.Pre-existing cement-based composites with microwave absorbing has some problems such as narrow frequency range,low absorbing efficiency,heavy weight,high cost which limited its application in building field.In connection with the problems of Pre-existing cement-based composites with microwave absorbing properties is present.This article carried out the research of the design and preparation methods of the core-stone structure wave absorber which was rely on the spheroidal resonant cavity theory,and the double layers cement based composite which was rely on the impedance matching theory,which provided theoretical basis for the research,preparation of cement-based composites with microwave absorbing properties.In this article,the main works and achievements are as below:According to the electromagnetic loss mechanism and the spheroidal resonant cavity theory,functional ceramisite was designed,namely the the core-stone structure wave absorber,which was coated with barium ferrite to enhance the capacity of electromagnetic loss of ceramisite.According to the impedance matching theory,double layers cement based composite which containing matched layer and loss layer was designed.In matched layer,perlite act as aggregate is added to improve matching impedance between composites materials surface with free space.In loss layer,functional ceramisite and cement paste with absorber act as absorber to enhance electromagnetic loss.This experiment used the Sol-gel to get the barium ferrite(BaFe₁₂O₁₉).The results showed that,among the different preparation conditions,when pH?7,barium nitrate:ferric nitrate:citric acid?molar ration?=1:11:19,1000?calcined 2h,the obtained sample with high purity were in the shape of sheet,the saturation magnetization?M_s?and coercivity?H_c?of the obtained sample was 46.7emu/g and3.83kOe.Functional cermisite coated with barium ferrite thin film are prepared by sol-gel under the vacuum negative pressure method.the result show that on the surface of cermisite,the elements characteristics peak of Fe are enhance,the elements characteristics peak of Ba are emerge.Functional cermisite take the place of original aggregate to prepared cement-based composites with microwave absorbing,and its properties are tested.The study shows that the aggregate type,functional cermisite content,the thickness and structure of the specimen have a big effect on absorbing properties of specimen.In8¹8GHz frequency range,the reflectivity of electromagnetic wave of the single-layer specimen with 60%vol functional cermisite and 30mm thickness is between-7.7to-8.0dB,the double-layers specimen is between-8.9 to-9.8dB.The compressive strength of 28d of this cement-base absorbing composites was 29.3 MPa.Nano-TiO₂,Nano-Fe₃O₄ and BaFe₁₂O₁₉ were doped to the cement-based absorbing composites with 60%vol functional cersimite respectively to prepared composites absorbing material.Results show that when the appropriate amount of nano absorbing agent are added,the electromagnetic wave absorption were improved differently,especially to the double-layer with matched layer.When the thickness of double-layer specimen is 30mm,the reflectivity of the specimen with 4%nano-TiO₂is lower than-10dB in the frequency range of 8GHz to 18GHz.In 8¹8GHz frequency range,the reflectivity of the 4%nano-Fe₃O₄ specimen is lower than-10dB,the minimum reflectivity of the specimen is-11.6dB.In 8¹8GHz frequency range,the reflectivity of the 4%BaFe₁₂O₁₉ specimen is between-9.9 to-11.4dB.The 28d compressive strength of this cement-based composites with 4%TiO₂ was 32.9 MPa.