Preparation Of Graphene/Fe₃O₄ Nano Microwave Absorbing Materials By 3D Printing And Mechanism Analysis

Using microwave absorbing materials can effectively solve the electromagnetic pollution problems caused by electrical equipment to human production and life.In addition,microwave absorption technology has become the most important technical means in the military equipment research and development.Graphene oxide?GO?/Fe₃O₄ nano absorbents with excellent microwave absorbing properties were synthesized in this research.Microwave absorbing inkjet ink containing this absorbent was prepared,which is used to fabricate absorbing material with blackbody structure by 3D printing technology.The absorbing mechanism of composite absorber and the blackbody structure of the material surface are revealed.A new way to prepare microwave absorbing materials has been developed,which greatly improves the applicability of microwave absorbing materials.Firstly,A new efficient method for the preparation of GO/Fe₃O₄ nanocomposites was proposed.X ray energy spectrometer,infrared spectrometer,raman spectrometer,transmission electron microscope,scanning electron microscope and other instruments are applied to test and analysis the microstructure,chemical composition and particle size of Fe₃O₄ nanoparticles,SiO₂ coated Fe₃O₄ and Graphene/Fe₃O₄ Nanocomposites.Different kinds,components,and content of microwave absorbers were added to a mixture of UV photocurable polyacrylate and methyl benzoate initiator,which were prepared to microwave absorbing materials by UV curing.The influence of microwave absorber'variations,composition,and content in species on the electromagnetic properties and microwave absorption properties of microwave absorbing materials,which were tested by coaxial method using vector network analyzer.The effects of light intensity,photoinitiator concentration,type and content of electromagnetic wave absorbers on photopolymerization kinetics were investigated by real time infrared spectroscopy?RT-IR?.In order to ensure the printability and curing speed of inkjet ink meet the requirements of 3D printing,the influence of the content of microwave absorbent on the printability and curing rate of microwave absorbing ink jet ink was studied,and the most suitable microwave absorber content was selected.Finally,four models of microwave absorbing materials with blackbody structure are established using 3D modeling software.Then,microwave absorbing materials with blackbody structure are prepared using 3D printer.The microwave absorbing properties of different materials in 6-40 GHz are tested according to GJB2038A-2011 for square flat materials:180×180×4 mm.And the mechanism of blackbody structure to improve microwave absorbing properties is revealed.The main results are as follows:1.The dispersion of Fe₃O₄ prepared by solvothermal method is poor,and the particle size of the cluster can reach more than 1?m,which is not conducive to composite with GO.SiO₂coated Fe₃O₄ nanoparticles have a good dispersion,the average particle size of Fe₃O₄nanoparticles are 20-30 nm,and the coating thickness is below 10 nm.SiO₂ coating can be condensed with GO under the action of catalyst after amination.Due to the large amount of carboxylon on the surface of GO is consumed during the reaction,the reduced graphene oxide?RGO?/SiO₂/Fe₃O₄ nanocomposite was formed.A large number of Fe₃O₄ nanoparticles were uniformly embedded on the GO,and the diameter of the particles did not change significantly during the composite process,which proved that the synthesis method had good effect.2.RGO/SiO₂/Fe₃O₄ nanocomposites have both electromagnetic properties of GO and Fe₃O₄.The dielectric constant of the composite is close to GO,the dielectric loss performance is better than GO,Fe₃O₄ and Fe₃O₄/SiO₂.The magnetic loss performance of the composite is less than Fe₃O₄,which is better than GO.The microwave absorbing properties of RGO/SiO₂/Fe₃O₄ nanocomposites are obviously higher than those of dielectric or magnetic medium materials,and the matching thickness is smaller and the absorption bandwidth is larger.The maximum reflection loss of the 5 mm thickness sample filled with GO as microwave absorber is only-14.32 dB at 7.67 GHz.The maximum reflection loss of the 5 mm thickness sample filled with Fe₃O₄ as microwave absorber is-35.26 dB at 9.64 GHz.The maximum reflection loss of the 5 mm thickness sample filled with Fe₃O₄/SiO₂ as microwave absorber is-51.3 dB at8.89 GHz,which is significantly higher than Fe₃O₄.The maximum reflection loss of the 4.5 mm thickness sample filled with RGO/SiO₂/Fe₃O₄ as microwave absorber is-56.38 dB at 8.14 GHz,and the bandwidth corresponding to reflection less than-10 dB?90%absorption?can reach 4.1GHz?from 6.5 to 10.6 GHz?for a layer of 4.5 mm thickness.The electromagnetic properties of RGO/SiO₂/Fe₃O₄ nanocomposites are greatly affected by the volume ratio of GO and Fe₃O₄.The electromagnetic properties of the composite are closer to GO and the electrical loss performance is better when the absorbent component is?volume ratio?GO:Fe₃O₄>1.When the component ratio is GO:Fe₃O₄<1,the electromagnetic properties of the composite are closer to Fe₃O₄,and the magnetic loss performance is better.The microwave absorbing properties of RGO/SiO₂/Fe₃O₄ nanocomposites are greatly affected by the filler capacity of GO and Fe₃O₄.When the mass ratio is GO:Fe₃O₄=7:3,the filling capacity of the two kinds of materials is the maximum and does not exceed the penetration point,and the microwave absorbing property of the material is the best.In addition,the content of absorbent also has a great influence on the electromagnetic properties and microwave absorbing properties of the materials,the material has the largest reflection loss when the mass ratio is 2‰.In summary,when the ratio of absorbent component is GO:Fe₃O₄=7:3,the mass ratio is 2‰,and the matching thickness is 4.5 mm,the sample has the largest reflection loss.3.The final conversion rate of double bond and relative reaction rate increase with the light intensity increasing.The effects of photoinitiator concentration on the final conversion rate of double bond and relative reaction rate are different,the final double bond conversion increased from 76%to 100%with the increase of initiator content.The final double bond conversion of ink contain graphene oxide is higher;the relative reaction rate of ink contain Fe₃O₄ is higher,the maximum relative reaction rate was reached within 10 s.When the content of electromagnetic wave absorber increases,the final conversion rate of double bond will decrease,and the reaction rate has a little change.When the content of glycol increases,the final conversion rate of double bond will decrease,and the reaction rate has a little change,the ink with glycol content of 20%has the maximum relative reaction rate.4.The particle size of the ink contain 0.25‰,0.5‰and 1‰microwave absorber are in the normal distribution between 200-300 nm,which are basically same as the special resin for 3D printer.The particle size of the ink contain 2‰microwave absorber is more than 500 nm,which has a poor dispersion,and can not meet the 3D printing requirement.With the increase of microwave absorbent content,the surface tension and viscosity of ink showed a downward trend.The surface tensions of the inks contain 0.25‰and 0.5‰microwave absorbers are 25.76mN/m and 25.94 mN/m.The viscosities of the inks contain 0.25‰and 0.5‰microwave absorbers are 0.1354 Pa.s and 0.1083 Pa.s,which are basically same as the special resin for 3D printer and able to meet 3D printing requirements.The relative reaction rates of the inks contain0.25‰and 0.5‰microwave absorbers are basically same as the special resin for 3D printer.Comprehensive consideration the printability and curing rate of the ink,which contains 0.5‰microwave absorber is best.5.The opening diameter of blackbody cavity in microwave absorbing material is 2.5 mm,when the 1/8 of the incident electromagnetic wave length is less than 2.5 mm?the electromagnetic wave frequency is greater than 15 GHz?,the waveguide effect will be obvious.At this time,the wave impedance of the material decreases,the electromagnetic wave entering the material increases,which is finally absorbed in the blackbody cavity after being reflected many times.Through the design of the blackbody cavity structure,increasing the reflection times of the electromagnetic wave in the blackbody can improve the absorption intensity and the absorption bandwidth of the material.The maximum reflection loss of solid plates is only-1.45 dB.The maximum reflection loss of conical cavity is-1.48 dB,the maximum reflection loss of inverted cone cavity is-2.78 dB,the maximum reflection loss of swallow tail cavity is-3.84 dB,the absorption performances of these models are greatly improved at more than 30Ghz.The maximum reflection loss of fishtail cavity is up to-5.92 dB,which have the better absorption performances at more than 20 GHz.The reflection loss of microwave absorbing materials made of four materials is placed in the middle,which is-3.93 dB.