Study On The Preparation And Electromagnetic Interference Shielding Properties Of Honeycomb Structured Ag@Ti₃C₂T_X Composites

Electromagnetic shielding materials have a great demand in the applications of civilian and military fields,to solve the problems caused by electromagnetic pollution.But the traditional electromagnetic shielding materials have the shortcoming of heavy mass,single structure and poor shielding performance.Therefore,new electromagnetic shielding materials should be developed to fit the trend of"thin,light,wide,strong"and multi-functional applications.In this thesis,the raw material Ti₃AlC₂ was etched by HCl and LiF,and the few layers of Ti₃C₂T_x well-dispersed aqueous dispersion was obtained by ultrasonication and centrifugation process.With Ti₃C₂T_x few layers of aqueous dispersion and Ag NO₃ as raw material,different honeycomb Ag@Ti₃C₂T_x-based composites can be prepared by template method,microwave hydrothermal and annealing heat treatment processes,respectively.Subsequently,the physical phase composition and microscopic morphology of these honeycomb composites were systematically analyzed,and then the electromagnetic shielding performance of each composite was evaluated and the mechanisms of electromagnetic shielding were also elaborated.The experimental research and related results of this work are as follows:（1）Few layers of Ti₃C₂T_x were first wrapped onto PMMA templates by mechanical stirring.The honeycomb Ag@Ti₃C₂T_x composites were obtained by loading Ag nanoparticles uniformly on the surface of Ti₃C₂T_x spheres through microwave hydrothermal,and PMMA templates were removed by annealing under argon protection.The as-prepared composites with a low density and light-weight exhibit improved electromagnetic shielding performance.Moreover,the annealed Ag@Ti₃C₂T_x composites are hydrophobic,thermal insulate and of good electromagnetic shielding performance.In this process,the Ag loading mass plays a key role in the altering electromagnetic shielding performance of the honeycomb Ag@Ti₃C₂T_x composites.It shows the Ag_-1.8@Ti₃C₂T_x composites exhibit the optimum electromagnetic shielding performance with the maximum average shielding performance of 39.36 d B at X-band（8-12 GHz）and 39.36 d B at K_u-band（12-18 GHz）.The mechanism could be attributed to the dielectric losses provided by Ag and Ti₃C₂T_x simultaneously,the interfacial polarization loss between Ag and Ti₃C₂T_x and the multiple reflections and scattering of electromagnetic waves caused by the pore structure in the honeycomb Ag@Ti₃C₂T_x composites.The synergy effects simultaneously promote the improvement of the electromagnetic shielding performance of the composites.（2）The effect of pore size of honeycomb Ag@Ti₃C₂T_x composites on the electromagnetic shielding performance is further studied.In this thesis,spherical PMMA templates with different particle sizes（1.8μm,5μm,and 10μm）were used to construct honeycomb structures in different pore sizes.The average electromagnetic shielding performance of Ag@Ti₃C₂T_x composite with 5μm pore size in X-band was 51.15 d B and in K_u-band was 56.64 d B.The enhanced electromagnetic shielding was mainly due to the dielectric loss,interfacial polarization,and multiple reflections and scattering of the honeycomb structure of Ag@Ti₃C₂T_x composite.（3）Based on the above study,honeycomb Ag@N-Ti₃C₂T_x composites with different degrees of nitride were obtained by controlling the hybridization content of N atoms.It is found that the samples have the optimum electromagnetic shielding performance when the nitriding time is 18 h.The average electromagnetic shielding performance in X-band was 52.38 d B and in K_u-band was 72.72 d B.The honeycomb Ag@N-Ti₃C₂T_x composite takes the advantages three-dimensional honeycomb structure and resulted multiple loss mechanisms,which can be used as a lightweight and efficient electromagnetic shielding material in future.