Preparation Of Fe/C Micro-Nano Fibers And Research On Their Microwave Absorbing Properties

The development of wireless communication technology has promoted the exchange of information between human society,but it has also brought a lot of electromagnetic pollution and endangered human health.Therefore,the research and development of high-efficiency microwave absorption materials has very important practical significance.Carbon fiber has the advantages of low density,stable properties,good electrical conductivity,and large specific surface area when used as absorbing materials.However,a single carbon fiber material has problems such as excessively high dielectric constant,poor impedance matching,and narrow absorption band.Therefore,how to modify or dope carbon fiber is a key issue to improve the absorbing performance of carbon fiber composites.In this paper,two technical routes are used to prepare Fe/C micro-nano fibers.The first technical route is to use PVP and PAN as polymer precursors,add iron salt,and undergo electrospinning and carbonization to obtain Fe/C micro-nano fibers;The second technical route uses natural loofah as a carbon source to obtain Fe/C fibers after iron salt impregnation and carbonization treatment.Through various characterizations,we explored the influence of carbonization temperature,solvent system and polymer precursors on the morphology,structure,electromagnetic properties and loss mechanism of Fe/C micro-nanofibers,and revealed the absorption mechanism.The main work content and results are as follows(1)The effect of carbonization temperature on the morphology,structure and properties of Fe/C micro-nano fibers was studied.At different carbonization temperatures(700?,730?,750?,800?),micro-nano fibers with the main phases of Fe and C were obtained,and some samples contained a small amount of Fe3C.The carbonization temperature has a great influence on the electromagnetic parameters of the material.When the carbonization temperature are 700?,730?,and 750?,as the temperature increases,the dielectric constant also increases.We analyzed the electromagnetic parameters of composites made of fiber and paraffin with different mass ratios(3:7,4:6,5:5),and found that as the mass fraction decreases,the dielectric constant decreases,the impedance matching is improved,and the absorbing performance is improved.(2)The effect of the solvent system on the morphology,structure and performance of Fe/C micro-nano fibers was explored.The surface tension,conductivity,volatility and solubility to ferric salts of the solvent system are different,and these differences will affect the final product.Although the diameter distribution of the fiber obtained from the solvent system containing deionized water is uneven,the internal Fe particles are larger in size,which provides higher magnetic loss,and therefore has better wave absorbing performance.The strongest reflection loss of the sample is-20.2 dB when the thickness is 2.0 mm,and the effective absorption bandwidth is 4.0 GHz when the thickness is 1.5 mm.(3)The effect of polymer precursors on the morphology,structure and properties of Fe/C micro-nano fibers was explored.Fe/C micro-nano fibers prepared with PVP and PAN respectively have different interfacial phases between the internal Fe particles and the carbon matrix.The Fe particles of the PVP-based fiber are outside the graphite carbon layer,and the Fe particles of the PAN-based fiber are Fe4N outside.The different interface phases have different effects on the properties of the material.The presence of Fe4N maintains the magnetic properties of Fe particles and has better absorbing properties.When the material thickness is 5.0 mm,the reflection loss value can reach-39.8 dB,and when the thickness is 2.5 mm,the effective bandwidth can reach 5.0 GHz.(4)The introduction of magnetic Fe particles into the natural loofah matrix can improve absorbing properties of the loofah-based fiber.The main body of the loofah is carbon,which provides dielectric loss;the introduction of Fe nanoparticles not only destroys the conductive network of the loofah,reduces the excessively high dielectric constant of the material,but also provides magnetic loss.The reflection loss value of the sample carbonized at 1000? can reach-48.9 dB when the thickness is 1.5 mm,and the effective bandwidth is 3.86 GHz,which achieves strong absorption under a thinner thickness.