A Study Of Absorption Properties And Preparation Of Polypyrrole-coated Sm And Dy-doped Barium Ferrite

Barium ferrite is commonly used as a wave absorbing agent because it has both magnetic loss and dielectric loss.However,because of its c-axis anisotropy,it has low magnetic permeability and high resonance frequency which limits the absorption of electromagnetic waves.Therefore,the sample needs to be modified.Metal or rare-earth element doping,material nano-crystallization and other methods are usually used to improve the electromagnetic parameters of materials.But the research on double rare-earth doped ferrite is relatively less.Therefore,polypyrrole-coated Dy-Sm doped barium ferrite composite wave-absorbing materials are prepared in order to improve the property of absorbing electromagnetic waves of the barium ferrite.The microstructure and performance of the samples were characterized by SEM,FTIR,VSM,VNA and other testing methods.Barium ferrite is prepared by sol-gel and self-propagating method.CTAB is used as the dispersant.The p H,the amount of citric acid and the dispersant were used as the variable to investigate their effect on the morphology and performance of the samples.The results show that when p H=7,n CA:n Ba²⁺=13,and C_CTAB=0.01mol/L,the flaky barium ferrite with minimal impurities can be prepared.When the thickness of composite material is 7.0mm,the reflection loss can reach-2.15d B at 14.64GHz.In order to improve the magnetic crystal anisotropy of barium ferrite,the rare-earth Dy and Sm doped barium ferrites were prepared under the above conditions.The doping amount was used as a variable to investigate the maximum doping of the two rare earth elements of doping separately and the proportion to obtain large reflection loss when rare earth elements are co-doped.The results show that when n Dy³⁺:n Ba²⁺=0.20 and n Sm³⁺:n Ba²⁺=0.10,the doping amount is the largest and there is no formation of rare earth iron oxide.Moreover,the doping of rare earth can increase the imaginary part value of the magnetic permeability of the sample and the material’s resistance to electromagnetic waves.When n Dy³⁺:n Ba²⁺=0.10 and n Sm³⁺:n Ba²⁺=0.050,a larger reflection loss can be obtained.The maximum reflection loss is-4.54d B（16.79GHz）and-4.00d B（16.00GHz）at the thickness of 7.0mm respectively.The maximum reflection loss can be obtained by co-doping with Dy-Sm doping.Especially when n Dy³⁺:n Sm³⁺=7:3 the reflection loss can reach-5.38d B at 15.38GHz when the thickness is 7.0mm.A layer of polypyrrole was coated on the surface of barium ferrite in order to increase the dielectric loss of the sample and obtain a large reflection loss.Ba Fe₁₂O₁₉@PPy composite absorption was prepared by in-situ polymerization using ferrous chloride and hydrogen peroxide as oxidants.The addition of pyrrole was set as a variable to explore its suitable adding amount to get a large amount of reflection loss.The results show that the reflection loss of the sample is the largest and the reflection loss of the coating is greater than that of the blend when m Py:m Ba Fe₁₂O₁₉=5:1.Ba Fe₁₂O₁₉@PPy composite absorbing material has the best absorbing performance.When the thickness is 7.0mm,the reflection loss of the sample can reach-12.46d B at 4.93GHz,the reflection loss can reach-23.24d B at15.82GHz,and the absorption bandwidth of less than-10d B can reach 4.81GHz.