Study On Preparation And Microwave Absorption Properties Of SiC Coated Modified Carbon Fiber Composites

In recent years,with the widespread use of wireless communications and electronic equipment,electromagnetic radiation pollution has become increasingly serious.The deteriorated electromagnetic environment will not only interfere with the normal work of electronic instruments and equipment,but also affect human health.Therefore,the development of new wave absorbing materials with excellent properties such as thin thickness,low density,wide frequency band,strong absorption,and high temperature resistance is imminent.SiC-coated carbon fiber composite materials make full use of the excellent high-temperature mechanical properties of fibers and the excellent dielectric properties of SiC.It has wide application prospects in daily electronic equipment and military strategic weapons.It is currently one of the most promising high-temperature structure and function integrated wave-absorbing materials.In this paper,using Si power as a silicon source,and glucose is a carbon source.Hydrothermal reaction combined with high temperature sintering method is used to synthesize SiC coatings with different structures and thicknesses on the surface of carbon fiber,and finally the carbon fiber/SiC composite wave absorbing material is prepared.The effects of catalyst type,thiourea content,and sintering temperature on the structure and properties of composite materials were studied.?1?First,C_f/SiC composite materials were synthesized by high-temperature sintering method using carbon fiber as raw material and Fe and Ni as catalysts respectively.As a result,the SiC nanowires covered by the C_f surface of the C_f/SiC composite material with Ni?C_f/SiC-II?as the catalyst are loose and unevenly distributed.At a material thickness of 1.5 mm,the minimum reflection loss is–14.61 dB at 8.20GHz,and the effective absorption bandwidth is only 0.23 GHz.The C_f surface of the C_f/SiC composite material with Fe?C_f/SiC-I?as a catalyst is closely packed with a large number of SiC arrays,which are evenly distributed and arranged in an orderly manner.When the material thickness is 1.3–1.8 mm,the minimum reflection loss is less than–20 dB,the minimum value is–40.65 dB,and the effective absorption bandwidth can be up to 2.42 GHz,which greatly improves the structure and absorbing performance of the composite material.?2?Next,still using carbon fiber as raw material,first use the hydrothermal method to generate the phase between the MoS₂ reaction mesophase on the surface of the carbon fiber.Then it was immersed in glucose solution,and Ni was used as catalyst to prepare C_f/MoSi₂/SiC composites by high temperature sintering method at different sintering temperature and thiourea content.The results show that the surface of the carbon fiber with a sintering temperature below 1450?tightly wraps the Si layer,and basically no SiC is formed.But at 1450?,the formed SiC nanowires are dense and evenly distributed.When the thiourea content is 93%and the material thickness is 1.5mm,the minimum reflection loss at 12.40 GHz is–19.10 dB,and the effective absorption bandwidth is only 0.78 GHz.At a thickness of 2.0 mm,the minimum reflection loss is reduced to–34.14 dB at 9.10 GHz,and the effective absorption bandwidth is increased to 2.18 GHz?8.20?10.38 GHz?.It can achieve the minimum reflection loss and maximum absorption bandwidth in a thinner thickness,and the wave absorption performance is more excellent.?3?Finally,bamboo fibrils/MoSi₂/SiC composites were successfully prepared by using bamboo fibrils instead of carbon fibers and hydrothermal reaction-high temperature sintering two-step method at different thiourea content.The surface of the bamboo fiber is uniformly covered with a layer of tightly bonded SiC coating,and as the content of thiourea increases,SiC gradually grows from particles to nanowires.The bamboo fiber/MoSi₂/SiC composite prepared with a thiourea content of 87%only obtains the lowest reflection loss at 18.76 GHz is–18.09 dB at a thickness of 2.5 mm,and the effective absorption bandwidth is 1.89 GHz?9.37–11.26 GHz?.