Preparation And Properties Of Graphene Functional Particles And Structural Miceowave Absorbing Composites

With the rapid development of military science and technology,radar detection performance has become more and more excellent.As a"shield"in warfare,the use of absorbing materials is an effective way to prevent self-discovery.Therefore,these materials are increasingly favored by researchers in related fields.Nowadays,due to the discovery of various kinds of high performance fibers,structural materials can really replace metals as stress structural components.At present,graphene can be modified by electroless plating.As a kind of natural fibers,basalt fibers have excellent mechanical properties,corrosion resistance and low cost.They are often used to reinforce composite materials.Epoxy resin has excellent mechanical properties,form and mass production is easy,and is often used as the matrix of composite materials.It can be used to prepare functional composites with high-performance fibers.Therefore,modified graphene/basalt fiber/epoxy resin composites were prepared by electroless plating modified graphene oxide as microwave absorbent,green basalt fiber were used as reinforcing fiber and epoxy resin were adopted as matrix.The main results of this study are as follows:?1?RGO/Ni composites were synthesized with NaH₂PO₂ as reductant and sodium citrate as crosslinking agent in NiCl₂ main salt solution at a certain pH.The electroless plating time was studied.It was found that the time parameters could control the amount of nickel particles adhered to graphene surface.The results show that nickel particles synthesized by electroless plating on graphene surface presents are spherical particles,and it is found that the amount and size of nickel particles are significantly affected by the time parameters.When the reaction time is 40 minutes,the nickel particles are evenly distributed,and the composite material achieves the best microwave absorption performance.The corresponding material thickness is only 3.00 mm,and the effective microwave absorption bandwidth is 4.00 GHz.For X-band,which is often used by radar,it basically achieves full-frequency coverage.In addition,when the thickness increases to 3.50 mm,the maximum absorption can reach-51.10dB.The absorption mechanism is further studied by quarter wavelength theory and improved impedance matching theory.The results show that the frequency dependence curve of RGO/Ni-40 microwave absorption performance conforms to the quarter-wavelength theory and slightly deviates from the optimal impedance matching condition.Through comparative analysis,it is found that the absorption performance of RGO/Ni-40 is mainly contributed by the quarter wavelength theory,while the effect of impedance condition is relatively weak.?2?Radar absorbing coatings were prepared by spraying RGO/Ni on the surface of basalt fiber.Each absorbing coating is a separate absorbing unit.Five type of absorbing coatings are studied through simple arrangement and combination design of absorbing coatings with different concentrations.The results show that if only one layer of absorbing layer is contained in the composite material,the absorbing performance is poor,when there are three layers of absorbing layer in the composite material,the transmission path of electromagnetic wave in the material is increased due to the increase of reflection and refraction of electromagnetic wave between the absorbing coatings,so the absorbing performance is better.It is found that the location of absorbing coatings with different concentration has a great influence on the absorbing properties.When the absorbing coatings are arranged in the form of concentration gradient,the absorbing properties are excellent.The maximum reflection loss is-11.82 dB,and the effective absorption bandwidth is 3.10 GHz.the impact strength reaches188.00 kJ/m²,and the bending strength reaches to 179.80 MPa,which corresponds to some requirements of load-bearing and stealth performance.Under these conditions,the material basically meets the dual requirements of mechanical properties and absorbing properties.In addition to surface treatment of fibers by spraying functional particles,silane coupling agent KH550 can also be used to modify basalt fibers,which can build a"bridge"between fibers and functional particles,and functional particles finally firmly adhere to the surface of fibers.After modification,the functional particles are arranged regularly on the basalt fiber,thus showing a sparse conducting network structure.The overlapping conducting network structure makes the composite material have better absorbing properties.The maximum reflection loss is-12.70 dB,and the effective absorbing bandwidth is 3.00 GHz.Compared with the unmodified basalt fiber,the surface of the modified fiber is smooth and becomes smooth.Roughness,increased surface contact area,and coupling agent improved the compatibility between fiber and matrix,so the mechanical properties were also improved,including impact strength increased by 20%,to 213.50 kJ/m²,bending strength increased by15%,to 238.20 MPa.?3?In order to improve the absorbing properties of the material,a functional composite material with three layers of transmissive layer,absorbing layer and reflective layer was designed.The effect of the thickness of the transmissive layer on the overall absorbing property of the composite material was systematically studied.The results show that the absorbing peak of the composite moves to lower frequency with the increase of the thickness,which indicates the absorbing property of the material.The frequency dependence curve satisfies the quarter wavelength theory.Because the transmissive layer can effectively guide electromagnetic waves into the material,the thickness of the transmissive layer has a great influence on the microwave absorbing performance of the material.It is found that the thickness of the transmissive layer and the microwave absorbing performance of the material are not simply linear,but there is an optimum value in a certain thickness range.When the thickness of the composite material is 5.00 mm,the maximum reflection loss is-15.44 dB,effective absorption.The bandwidth is 0.90 GHz,the impact strength is 175.63 kJ/m² and the bending strength is 228.23 MPa,which basically meets the requirements of stealth performance and load-bearing performance.