Study On Electromagnetic Wave Absorption Properties Of Chromium-based Compound Composite

With the maturity of 5G technology and its large-scale application in communication signal and other fields,the communication technology with electromagnetic wave as the main carrier has been further popularized.However,with the wide spread of electromagnetic wave communication,some problems caused by electromagnetic wave have become increasingly prominent.The problems caused by electromagnetic wave not only threaten the safety of the ecological environment,but also have an unpredictable impact on human health.Therefore,it can be predicted that electromagnetic waves will pose a certain threat to human beings in the future.At the same time,stealth and anti-stealth technology in modern warfare also has a strong dependence on electromagnetic waves.In order to improve the ability of weapons and equipment such as combat units and aircraft to avoid reconnaissance and detection,different types of electromagnetic wave absorption and shielding materials have been widely developed and applied.These materials mainly achieve certain strategic objectives by reducing the electromagnetic wave signals sent by themselves and influencing the electromagnetic waves detected by the opponents.Therefore,efficient electromagnetic wave absorbing materials that attenuate various frequency bands of electromagnetic waves have been widely studied by researchers,and the development of materials with excellent electromagnetic wave absorbing properties has gradually become one of the hot spots pursued by scientists.According to existing reports,carbon materials are often conductive and can obtain large specific surface area through different processes.At the same time,carbon materials also have excellent mechanical properties.Through processing,carbon-based materials can be used as electromagnetic wave absorbing materials.At present,many kinds of carbon materials have been used in the field of wave absorption.For example,graphene,carbon black,carbon nanotubes,carbon cloth,etc.However,carbon material itself does not have any magnetism.Its electromagnetic wave absorption and loss mainly depend on dielectric loss.It is difficult for a single component to achieve excellent absorption effect.Transition metal has unique applications in various electromagnetic wave absorption due to its unique characteristics.Various electromagnetic wave absorption materials loaded with transition metal compounds have been widely developed and applied to practical applications,Therefore,researchers usually doped metal particles to obtain electromagnetic wave absorbing composites with excellent performance.As a metal element,chromium combines with different elements to form compounds that often have unique stability and magnetic properties.After high temperature treatment,the chromium oxide crystal form is compact,resistant to acid and alkali corrosion,and has good adhesion ability;Chromium compounds are hard,chemically resistant substances that can resist corrosion and oxidation.It has different applications in improving mechanical properties,thermal stability and oxidation resistance of alloys.In this paper,various chromium compounds are taken as the research object,and they are used as load to prepare different composite materials.It is expected to promote the absorption of electromagnetic waves through the introduction of transition metal compounds,enhanced multi-polarization and the coordination of dielectric and magnetic properties,and improved transmission path of electromagnetic waves in the material.Realize the synergistic effect of multiple electromagnetic wave absorption mechanisms of materials,and realize the electromagnetic wave absorption materials with controllable dielectric and magnetic properties.The research contents and results of this paper are as follows:（1）Using EDTA-2Na as raw material,we prepared porous carbon precursor materials by calcination.We calcined EDTA-2Na at 700°C in argon atmosphere,and calcined at high temperature to decompose the organic nitrogen-rich skeleton of EDTA molecules to produce nitrogen-doped porous carbon materials.At the same time,the sodium species were converted into sodium salts（sodium carbonate,etc.）in situ.The decomposed carbon-containing and nitrogen-containing groups are converted into carbonated products on the sodium salt particles.The sodium salt is removed by washing with deionized water,and then the activated product is calcined at 500°C in argon atmosphere for 3h by activating the pore formation by the aqueous solution containing the same mass of KOH,and the unreacted KOH is washed off with hydrochloric acid to obtain the nitrogen-doped porous carbon precursor.Preparation of reaction at 120°C for 5 h by water bath heating NiCo₂Cr_x-OH@C To be collected NiCo₂Cr_x-OH@C Annealed in H₂/Ar environment,partial reduction of hydroxide was achieved at high temperature,and the final product NiCo₂-0.5x Cr₂O₃@C was collected.The results show that the minimum reflection loss of NiCo₂-0.5Cr₂O₃@C is-52.71 d B at 1.6 mm,and the effective absorption bandwidth range is 5.28GHz at 1.89 mm.（2）On the basis of previous experiments,taking into full consideration the characteristics of different magnetic transition metal particles and their impact on the electromagnetic wave absorption ability of materials,we use Fe and Cr to form an oxide system.According to previous reports,we used the prepared porous carbon precursor to grow Fe-Cr-OH colloid on the porous carbon by hydrothermal reaction at 120°C for 5hours.After fully drying and heating to remove moisture,we calcined it at high temperature under H₂/Ar environment to make it reduced to uniform Fe-Cr-O oxide film structure attached to the surface of the porous carbon,forming a film structure attached Fe-Cr-O@C compound material.By controlling the proportion of Fe-Cr to find the appropriate doping amount,we can obtain the electromagnetic wave absorption composite material with wide effective absorption bandwidth at low thickness.The effective absorption bandwidth achieved 4.08GHz at 1.5mm,while the minimum reflection loss occurs at 2.2mm,and its reflection loss value is-51.22d B.（3）Taking into account the characteristics of metal particles and organic raw materials at high temperatures,we proposed a feasible research plan to prepare a multi-component carbon nanotube composite containing cobalt,copper and chromium nitride.We first prepared cobalt,chromium and copper hydroxide by hydrothermal method,and then mixed it with different proportions of dicyandiamide,which was calcined at high temperature under protective atmosphere,High temperature calcination can decompose the hydroxide into oxides,and the carbon generated at this time will show a certain reduction at high temperature,and chromium will combine with the amino group of the organic raw material dicyandiamide.We have successfully prepared a cobalt/copper/chromium nitride/carbon nanotube composite Co/Cu/CrN/CNTs by calcining at high temperature,and further improve its electromagnetic wave absorption performance by introducing the synergistic effect of various components.The results show that when the ratio of intermediate and dicyandiamide is 1:40,the material has the best electromagnetic wave absorption performance.The maximum reflection loss can reach-56.54 d B at 2.37 mm,the maximum effective absorption bandwidth appears at 2.01 mm,and the effective absorption bandwidth is 5.92 GHz.