Study On Electromagnetic Functional Materials Derived From Melamine And Their Properties

With the rapid development of 5G communication technology and various miniaturized electronic devices,the progress of science and technology has greatly enriched our daily life.However,it also brings problems of electromagnetic radiation pollution that cannot be ignored,such as human damage,information leakage,environmental pollution and so on.Therefore,it is very important to study new electromagnetic functional materials(wave absorbing materials and wave absorbing materials).As a common chemical raw material,melamine has the advantages of abundant raw materials,low cost,high nitrogen content and carbon content.In order to explore the potential application value of melamine in the field of electromagnetic function,we use melamine as the raw material,using different processing technology to give it different properties,to prepare new melamine derived electromagnetic function materials.Specifically,in this paper,melamine is used as one of the raw materials,and it is treated with boric acid,metal salt particles(nickel chloride)and metal oxides(nickel oxide)in different processes to obtain electromagnetic functional materials with excellent performance.With the help of common characterization methods,such as Xray diffraction(XRD),Raman spectrometer(Raman),X-ray photoelectron spectroscopy(XPS),field emission scanning electron microscope(FESEM)and transmission electron microscope(TEM),the phase and structure are characterized,and the electromagnetic parameters are tested by vector network analyzer(VNA).The main contents of this paper include:(1)Hexagonal boron nitride nanofibers with high specific surface were prepared by precursor pyrolysis using boric acid,melamine and PEG as raw materials.The effects of different drying methods(air drying,vacuum freeze-drying)and PEG content on the morphology and specific surface area of the precursor were investigated and optimized.The results showed that the diameter of h-BN nanofibers increased with the increase of the ratio of boric acid to melamine.The aspect ratios of h-BN nanofibers increased from 20 to 30 after lyze-drying,and the specific surface area increased from 65.25 m2/g to 319.07 m2/g.In addition,PEG content also significantly increased the specific surface area.When PEG content reached 2%,the surface area of h-BN nanofibers prepared by drying precursor system increased 12.4 times to 874.58 m2/g compared with that without PEG addition.Moreover,the dielectric constant and dielectric loss of the prepared h-BN nanofibers were very low,which could be used to prepare wave-permeable materials.(2)3D multi-interface carbon nanotube networks were in-situ constructed from graphitic carbon nitride(g-C3N4)and nickel chloride as raw materials.The obtained Ni@CNTs exhibited high electromagnetic absorption performance with the filler loading content of 3 wt%in paraffin.The minimum reflection loss of 0.2Ni@CNTs was dramatically enhanced to-31.7 dB and the effective absorption bandwidth was 6 GHz.The phase conversion process of melamine during pyrolysis and the phase reaction with metal salt particles were studied in detail.The results showed that during the pyrolysis process,melamine was converted into graphitic carbon nitride(g-C3N4),and further decomposed into a large number of C-N components.The metal salt particles were reduced to obtain metal nanoparticles,and the structure of carbon nanotubes was further catalyzed.Moreover,a large number of interface structures increased the interfacial reflection of the material,which improved the impedance matching and was conducive to the improvement of the microwave absorption performance of the material.(3)For microwave absorbers,it was still a tremendous challenge to efficiently construct multidimensional heterostructures to realize the synergy of multi-component and multi-loss modes.On the basis of the above experiments,a kind of cocklebur-like Ni@C-CNTs multidimensional heterosphere was obtained by a simple metal oxidetemplate method using graphitic carbon nitride(g-C3N4)and nickel oxide as precursors.The results showed that metal oxides tend to aggregate to form heterogeneous spheres during pyrolysis.The conductive network formed by carbon nanotubes and heterogeneous spheres not only increased the conduction loss of the materials,but also promoted the multiple reflection absorption inside the materials.In addition,the cocklebur-like heterostructure had many defects and interfaces,which effectively realized the synergistic effect of various loss mechanisms including conduction loss,interface polarization and dipole polarization.Accordingly,with a filler loading of 30 wt%,the minimum reflection loss of the resulting Ni@C-CNTs heterospheres was up to-41.60 dB,and the effective absorption bandwidth reached 4.1 GHz when the matching thickness was 2.4 mm.