Synthesis Of Porous Carbon Composites And Research In Electromagnetic Wave Absorption Performance

With the progress of science and technology,electromagnetic waves occupy a very important position in human daily life,but with the widespread use of electromagnetic waves,electromagnetic waves also have a great impact on human health and the survivability of weapons and equipment.First of all,long-term exposure to complex electromagnetic wave environment will bring many negative effects on human spirit and other aspects,at the same time,at this stage in the military field,especially in the aerospace field,are required to prevent electromagnetic wave interference,therefore,electromagnetic wave absorbing materials are more and more attention by researchers,at this stage the requirements for electromagnetic wave absorbing materials are mainly low density,i.e.,light mass,strong absorption performance,effective absorption bandwidth is large.With the research in recent years,porous carbon materials have a very large electromagnetic wave absorption potential due to their low density and excellent electrical conductivity because they have a large number of internal cavities,but simple porous carbon materials have impedance mismatch and other shortcomings,resulting in their electromagnetic wave performance is not excellent,so it is necessary to optimise their structure and component design in order to make their dielectric parameters adjustable and impedance matching excellent,and ultimately achieve excellent electromagnetic wave absorption performance.The main findings of the study are as follows:（1）Structural optimization of porous carbon materials to further improve the dielectric properties and impedance matching of porous carbon materials.EDTA,EDTA-2Na and EDTA-4Na were used as carbon sources to prepare the porous carbon precursors through annealing process,and then the porous carbon materials were prepared by making pores with activators.To further improve the dielectric properties of the porous carbon,EDTA-2Na was used as the precursor of the porous carbon and a simple polyaniline coating process was used to synthesise a porous carbon@polyaniline composite with high porosity.The minimum reflection loss(RL_min)was-72.16 dB and the effective absorption bandwidth（EAB）was 6.64 GHz（10.16-16.8 GHz）at a matched thickness of 2.6 mm.（2）In order to make the electromagnetic wave absorption performance of porous carbon become more excellent and increase the electromagnetic wave absorption mechanism of porous carbon,NiCo₂S₄,a bimetallic sulfide with spinel structure,was introduced into porous carbon and compared with monometallic sulfide,specifically,ZIF-67 was first grown on porous carbon,which was subsequently carbonized into metallic cobalt monomers,and then Nielement was introduced into the system The NiCo₂S₄@C/PC composite was finally vulcanised to form NiCo₂S₄@C/PC.The addition of the bimetallic sulphide resulted in more loss mechanisms of the porous carbon to electromagnetic waves,the most obvious being the introduction of magnetic loss,which was tested to give an RL_minof-59.36 dB and an EAB of 6.8 GHz when the thickness was 2.1 mm,with the performance of the bimetallic sulphide being better than that of the but the performance of the metal sulphide is superior to that of the but-metal sulphide,and the absorbing properties of the porous carbon composite are enhanced when dielectric and magnetic losses interact,especially when the matched thickness and EAB are further enhanced compared to the single loss regime.（3）Co@CNT/PC composites were obtained by sequentially growing ZIF-8 and ZIF-67 on porous carbon and then annealing at high temperature.by test analysis,metallic cobalt can catalyze the carbon in the system to generate carbon nanotubes（CNTs）at high temperature.the CNTs evaporated from the system and the addition of CNTs made more interfaces appear in the system,which made the interfacial polarization of Co@CNT/PC composite the interfacial polarisation increases significantly and the wave absorption performance is improved,with RL_min reaching-56.23 dB at a thickness of 2.3 mm and EAB reaching 7.36 GHz（10.64 GHz-18 GHz）at 2.3 mm.Finally,by designing the structure and components of porous carbon,not only the impedance matching of porous carbon is improved,but also the absorbing mechanism of porous carbon is increased,and the combination of dielectric and magnetic losses can achieve the regulation of the absorbing performance of porous carbon composites,so as to obtain electromagnetic wave absorbers with excellent performance.