Preparation And Microwave Absorbing Properties Of Dimensional MXene And Its Composites

With the development of science and technology,various high-frequency electronic communication equipment and high-power electronic and electrical equipment have been widely used,and the electromagnetic radiation caused by them has been paid more and more attention.At the same time,there are more and more requirements for absorbing materials.The ideal absorbing material should have the characteristics of strong loss ability,thin absorption thickness,wide absorption band and light weight.In recent years,two-dimensional MXene has become a promising research material in the field of microwave absorbing materials due to its unique layered structure,inherent defects and a certain degree of conductivity.The pure two-dimensional MXene shows metal characteristics,and the MXene prepared by chemical etching has various functional groups on its surface,showing semiconductor characteristics.Its absorbing mechanism is mainly dielectric loss,and its absorbing mechanism is single,and its absorbing efficiency and effective absorbing bandwidth need to be improved.In this paper,two-dimensional MXene and its composite materials are taken as the research objects,and the materials are characterized by XRD and SEM.the electromagnetic parameters of the materials are measured by vector network analyzer,and the absorbing properties of the materials are simulated.Finally,the absorbing mechanism of the materials is discussed.The main research contents of this thesis are as follows:(1)Ti₃Al C₂ceramics were synthesized by pressureless sintering method,and the effect of Al content on the purity of Ti₃Al C₂ceramics was studied.It is found that when the molar ratio of Ti,Ti C and Al is 1?2?1.2,the purity of Ti₃Al C₂ceramics is the highest.The effects of etching time and temperature on the structure and microwave absorbing properties of Ti₃C₂materials were studied by chemical liquid etching method with the ceramics as precursor and HF with mass fraction of 40%as etchant.The results show that when the etching time is 8h and the etching temperature is 25?,the Ti₃C₂material has the best wave absorbing performance.When the matching thickness is 2.6mm,the reflection loss reaches an extreme value of-31.6d B at 11.3GHz and the effective absorption bandwidth is about 0.61GHz(10.95?11.56GHz).The higher absorption strength of Ti₃C₂material may be attributed to the fact that there are more impurities Al³⁺in the material under short etching time and low etching temperature,and the relaxation polarization and dipole polarization are obvious.In addition,the layered structure and high specific surface area of Ti₃C₂material can cause multiple reflection and scattering of electromagnetic waves and interface polarization,which will further attenuate electromagnetic energy.(2)Ag particles were deposited on the surface of Ti₃C₂substrate by electroless plating.The effects of main salt concentration and dispersant on the structure and microwave absorbing properties of composite powder were discussed.It is found that with the increase of the main salt concentration,the microwave absorbing properties of the composites first decrease and then slowly increase.When the main salt concentration is 5.27g/L and the sample thickness varies from 1.2 to 1.9 mm,there is an effective absorption band(?-10d B)in the test frequency range.Especially when the matching thickness is 1.3mm,the reflection loss reaches an extreme value of-24.06d B at 11.12GHz and the effective absorption bandwidth is2.2 GHz(10.2 GHz?12.4 GHz).When the matching thickness is 1.4mm,the reflection loss reaches an extreme value of-28.49d B at 10.24GHz and the effective absorption bandwidth is1.93GHz(9.42GHz?11.35GHz).At the same time,the impedance matching performance of the sample at this main salt concentration is also the best.After adding dispersant,the relationship between the reflection loss and the thickness of the sample changes.With the increase of the thickness of the sample,the absorption peak shifts to low frequency,and the absorption intensity first increases and then decreases.Impedance matching performance is also enhanced.With the addition of Ag particles,the micro-morphology of Ti₃C₂was changed and the electromagnetic parameters of the material were optimized,so the microwave absorbing performance of the material was improved.The analysis of microwave loss mechanism of each sample shows that the loss mechanism of samples mainly includes polarization loss,conductance loss and interference cancellation.(3)Co particles were deposited on the substrate surface by electroless plating to prepare Ti₃C₂/Co composites.The effects of main salt concentration and buffer on the structure and microwave absorbing properties of composite powders were discussed.It is found that with the increase of main salt concentration,the absorption strength of the sample increases,and the impedance matching performance is improved first and then decreased.When the concentration of main salt is 60g/L,the matching thickness is 1.9mm,the reflection loss reaches the extreme value of-8.98d B at 11.75GHz.When the matching thickness is 2.0mm,the reflection loss reaches the extreme value of-8.68d B at 11.46GHz.Although there is no effective absorption bandwidth in the samples after electroless plating,compared with the substrate,the matching thickness of the samples after electroless plating is reduced under the same absorption strength,which indicates that the absorbing performance of the samples after electroless plating of Co is improved.After adding buffer,the absorption strength of the sample is enhanced,when the sample thickness is 1.9mm,the absorption intensity at10.36GHz is-9.86d B,when the sample thickness is 2.0mm the absorptiom intensity at10.26GHz is-9.59d B,and the impedance matching performance is optimized at high frequency.Because the layered Ti₃C₂material is a dielectric loss absorbing material,and the loss mechanism is single,the introduction of metal Co can not only introduce a new loss mechanism,but also improve the impedance matching performance of the material.The study on microwave loss mechanism of samples shows that the loss mechanism of samples mainly includes polarization loss,natural resonance,exchange resonance,conductance loss,and interference cancellation.