Microwave Absorbing Properties Of Magnetic Metal And Its Composites After Corrosion Process

Metal soft magnetic materials have higher saturation magnetization in GHz frequency,which makes them have good absorbing performance in radar wave frequency band.Therefore,metal soft magnetic materials are widely used in the field of electromagnetic wave absorption.As a two-dimensional crystal,graphene has excellent mechanical,optical,electrical and thermal properties.Graphene is easy to form multi-layer composite structure,which can greatly promote the electromagnetic wave loss.Therefore,graphene is widely used in the doping modification of microwave absorbing materials to improve the electromagnetic absorption performance of doped graphene composite absorbing materials.In this paper,two kinds of metal soft magnetic materials(FeCoV and FeSiCr)were used to prepare magnetic metal composite absorbing materials by doping calcium stearate(Y)and graphene oxide(GO).The microstructure and electromagnetic parameters of composite absorbing materials in different corrosive media(5%Na Cl solution and H₃PO₄ phosphate acid)were studied.The microwave absorbing properties of magnetic metal composite materials after corrosion was evaluated.The other work is to study the rapidly quenched magnetic metal Nd-Co doped with rare earth Nd.The effects of different post treatments on the microwave absorbing properties for Nd₂Co₁₇ alloys were evaluated.(1)The FeCoV alloy powder is doped with GO and Y,and the FeCoV/GO/Y composite absorbing material is prepared by high-energy ball milling.The corrosion experiment was carried out by static immersion treatment with Na Cl and dilute H₃PO₄.SEM results show that the composite microwave absorbing materials keep sheet structure before and after corrosion,but the addition of Y reduces the agglomeration of particles.The results of energy spectrum show that iron oxide may be formed on the surface of the composite absorbing material after corrosion,and the oxide formed on the surface of FeCoV/GO/Y composite is obviously more than that of FeCoV material.The measurement results of electromagnetic parameters show that FeCoV/GO/Y composite absorbing materials can maintain the original electromagnetic parameters to the greatest extent after corrosion,while the complex permittivity of FeCoV materials without doping fluctuates abnormally.Regarding the electromagnetic properties of the material,the results show that the surface modification and the formation of oxides are helpful to alleviate the adverse effect of corrosive solution.The reflection loss(RL)calculation based on transmission line theory shows that when the thickness is 1.5mm,the minimum reflection loss of FeCoV/Y material after salt solution corrosion and phosphoric acid corrosion are-10.5d B and-8.9d B,respectively.Compared with the minimum reflection loss of FeCoV after salt solution corrosion(-5.8d B)and phosphoric acid corrosion(-8d B),the minimum reflection loss is significantly reduced.Similarly,the absorption bandwidth of FeCoV/GO composite after salt solution corrosion(range below-5d B reaches 2.8GHz)is much higher than that of FeCoV after salt solution corrosion(1.1GHz).It is more noteworthy that the minimum reflection loss of FeCoV/GO/Y composite absorbing sample after salt solution corrosion is-11d B,and the absorption bandwidth(less than-5d B)is 4.5GHz,which is much larger than that of the FeCoV after salt solution corrosion.Under the corrosion behavior,the advantages by doping GO or Y alone in the microwave absorbing performance can be obtained simultaneously by doping GO and Y together.(2)FeSiCr/GO/Y composite absorbing materials are prepared by high-energy ball milling,and their microwave absorbing properties under corrosive conditions are evaluated.SEM results show that all the composite samples and FeSiCr still show typical sheet structure after corrosion,but some fine particles appear on the surface of FeSiCr/GO composite.The energy spectrum analysis shows that the fine particles on the surface of FeSiCr/GO composite may be GO.When the thickness is1.5mm,the minimum reflection loss(RL)of FeSiCr is-9.8d B.After phosphoric acid corrosion and salt solution corrosion,the minimum reflection loss of FeSiCr is-8.4d B and-8.9d B,that is to increase14%and 9%respectively.While the minimum reflection loss of FeSiCr/GO after phosphoric acid corrosion is only 5%increase compared with that before corrosion;The minimum reflection loss of FeSiCr/Y after corrosion in the salt solution is not increased but reduced by 8%compared with that before corrosion.It is shown that doping GO and Y can effectively alleviate the adverse effects of the above corrosion process on the microwave absorbing properties.The minimum reflection loss of FeSiCr/GO/Y composite absorbing material in salt solution corrosion is-10.7d B,which is lower than the minimum reflection loss of FeSiCr/GO/Y composite absorbing material before corrosion(-9.6d B).The minimum reflection loss in phosphoric acid corrosion environment is only 7%higher compared with that before corrosion.The composite doped GO/Y combines the advantages of single doped GO or Y on absorbing properties,which is similar to the previous research results of FeCoV alloy absorbing materials.(3)The Nd₂Co₁₇ alloy particles were prepared by melt spun and high-energy ball milling techniques.Vacuum heat treatment or crushing method were added during the manufacture period to obtain absorbing powders.The microstructure and electromagnetic properties of absorbing powders were studied.The electromagnetic parameters were studied by an Agilent vector network analyzer.The size and thickness of the crushed alloy powders distinctly decreased compared with that of the uncrushed sample.The reduction in size and thickness of alloy powers can significantly enhance electromagnetic matching for absorbing powders.Consequently,the microwave absorption properties of the crushed alloys were significantly improved.The reflection loss(RL)which is based on transmission line theory shows that the vacuum heat treatment sample had the RL peak in C-band.However,the crushed sample had the RL peak between the C-band and the X-band.The minimum RL value of-8.1d B was obtained at 8.2GHz for crushed Nd₂Co₁₇ alloy,and the absorption bandwidth less than-5d B was up to 9.4GHz.In contrast,the RL peak of the Nd₂Co₁₇alloys without post treatment was located in S-band.It is proved that proper post treatment is the key to regulating the electromagnetic matching,thus the optimal microwave absorption properties of the alloys can be obtained in different bands.