Study On Electromagnetic Wave Absorption Properties Of Multi-dimensional Reduced Iron Powders And Their Composites

From daily communications to military information operations,electromagnetic waves have played an important role.However,the widespread application of electromagnetic waves has also caused electronic pollution,which not only endangers human health,but also causes disturbances in information transmission.Therefore,the development of absorbing material that can efficiently absorb electromagnetic waves has become a hot spot of current research.At this stage,carbonyl iron powder is a widely used absorbing material,but it has the disadvantages of high price and unfriendly environmental protection.Therefore,this paper is devoted to improve the shortcomings of poor impedance matching and poor oxidation resistance of iron powder on the basis of using reduced iron powder with low cost and environmentally friendly manufacturing process instead of carbonyl iron powder.First of all,the electromagnetic parameters of iron powders with different dimensions are significantly different.In this paper,flake reduced iron powder and nano-iron wires were prepared,and the differences in the absorption properties of wires,flakes,and spherical iron powder were compared.Secondly,coating iron powder is an effective way to enhance its oxidation resistance,optimize impedance matching,increase loss mechanism,and improve interfacial polarization effect.In this paper,reduced iron powder and nano-iron wires were used as the matrix,and both were coated with SiO2 and carbon to make a composite materials.The change of the absorbing property was analyzed.This article is dedicated to obtaining lightweight,efficient and practical absorbing materials.The main researches are as follows:(1)First,reduce the ore powder by hydrogen reduction method to obtain spherical reduced iron powder with different particle diameters.Compare with spherical commercial carbonyl iron powder with the same particle diameter,and use high energy ball milling method to ball mill both into flakes.The study found that the reduced iron powder and carbonyl iron powder with the same spherical particle size had poor wave absorbing properties.The lowest reflection loss of the flake reduced iron powder is 2.59 mm at the frequency of 9.6 GHz,and the lowest reflection loss is-56.4 dB.The effective absorption band of the reflection loss is less than-10 dB is 7.7～12 GHz,and the range is 4.3 GHz.Iron powder has a minimum reflection loss of-43.0 dB at a thickness of 2.63 mm,the frequency at 8.4 GHz,an effective absorption band of 6.9 to 10.1 GHz,and the range is 3.2 GHz.As a wave absorbing material,the wave absorbing effect of reduced iron powder is better than that of carbonyl iron powder.(2)The flake reduced iron powder and nano-iron wire were made by high-energy ball milling wet method and redox method,respectively,and the absorbing performance was analyzed.The spherical reduced iron powder was put into a high-energy ball mill for ball milling.It was found that the flake reduced iron powder prepared at a ball milling speed of 240 r/min and a ball milling time of 10 h had a minimum reflection at a coating thickness of 2.59 mm and frequency at 9.6 GHz.The lowest reflection loss is-56.4 dB,the effective absorption band is 7.7～12 GHz,and the range is 4.3 GHz.The nano-iron wires are synthesized using FeCl3·6H2O and NaBH4 as raw materials.Experiments show that when the speed of the peristaltic pump is 60 r/min and the mass ratio of FeCl3·6H2O and NaBH4 is 0.6:0.2,the synthesized nanoiron wire has a minimum reflection loss of-47.3 dB at thickness of 1 mm and a frequency of 17.8 GHz,which the effective absorption band is 16.2～18.0 GHz,and the range is 1.8 GHz.The flake reduced iron powder mainly has magnetic loss for electromagnetic waves,and the nano-iron wire is a composite loss that has both magnetic loss and dielectric loss effectting on electromagnetic waves.(3)The sol-gel method and hydrothermal method were used to coat the sample with SiO2 and carbon respectively,and the change of the absorbing property was studied.After adding 1.5 mL TEOS to flake reduced iron powder coated SiO2,the minimum reflection loss at a thickness of 1.6 mm is-38.4 dB,the frequency is 16.7 GHz,the effective absorption band is 13.4 to 18 GHz,and the range is 4.6 GHz.After adding 0.8 mL TEOS to the nano-wires coated SiO2,the minimum reflection loss reaches-39.6 dB at a thickness of 1.37 mm,the frequency is 16.7 GHz,the effective absorption band is 14.9～18 GHz,the range is 3.1 GHz;After adding 0.3 g glucose to flake reduced iron powder coated carbon layer,the thickness of 1.8 mm,a minimum reflection loss of-39.1 dB when frequency at 15.3 GHz,the effective absorption band is 12.3 to 17.8 GHz,and the range is 5.5 GHz.Finally,the flake iron powder first coated SiO2 by sol-gel method,and then coated carbon layer by hydrothermal method.The double-layer coated sample has a minimum reflection loss of-72 dB at a thickness of 1.86 mm when frequency at 14.6 GHz,The effective absorption bandwidth of reflection loss below-10 dB is 11.8～6.8 GHz,and the range is 5 GHz.After coating the sample,the thickness is effectively reduced,the effective absorption bandwidth is expanded,and the absorption effect is improved comprehensively.