Preparation And Characterization Of Carbon Chains And Study Of Microwave Absorption Properties Of CoFe₂@SWCNT/BaFe₁₂O₁₉

One-dimensional carbon atom chains and single-walled carbon nanotubes（SWCNTs）have attracted more and more attentions due to their unique structures and properties for several decades.This thesis includes the study of preparation and applications of carbon atom chains（polyynes）and single-walled carbon nanotubes.Firstly,polyynes were prepared by arc discharge in liquid organic solvent and separated by high performance liquid chromatography（HPLC）.Then,to improve polyynes’stability,they were mixed with polyvinyl alcohol（PVA）powders to obtain transparent film.Secondly,high-quality CoFe₂@SWCNTs were prepared by direct current arc discharge evaporation of graphite powder with homogenously doped Co（1at.%）and Fe（2 at.%）catalyst in an H₂-Ar gas mixture.The BaFe₁₂O₁₉ nanoparticles were made by a nitrate citric acid sol-gel auto-ignition method.Then,the electromagneticandmicrowaveabsorptionpropertiesofthe CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposite were systematically investigated by a vector network analyzer in the frequency range of 2-18 GHz.In the first part,polyynes were prepared in methanol and hexane by arc discharge method.The original solution was concentrated by evaporation and separated by HPLC.Surface enhanced Raman spectroscopy（SERS）were measured by adding Ag nanoparticles.Polyynes were mixed with PVA to obtain transparent film.Raman results show that polyynes exist in PVA film for several months.According to references,there may be interaction between polyynes and Ag nanoparticles which may form Ag-C₈-H or Ag-C₈-Ag modes.To verify the speculation,nuclear magnetic resonance（NMR）,infrared spectrometer（IR）,x-ray photoelectron spectroscopy（XPS）and x-ray diffraction（XRD）detections were performed.However,there is no direct evidence for the existence of C-Ag bond.This may be explained as the low concentration for polyynes.In the second part,high-quality CoFe₂@SWCNTs were prepared by direct current arc discharge evaporation of graphite powder with homogenously doped Co（1at.%）and Fe（2 at.%）catalyst in an H₂-Ar gas mixture.The BaFe₁₂O₁₉ nanoparticles were made by a nitrate citric acid sol-gel auto-ignition method.The effects on the microwaveabsorptionpropertiesofthedifferentweightratio CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposite samples in paraffin matrix were investigated and structure characterization of the samples were given.The S parameters of the samples were measured in the frequency range of 2-18 GHz by a vector network analyzer.The effective relative complex permittivity and effective relative complex magnetic permeability of the nanocomposites could be calculated by S parameter using the NRW algorithm.The dielectric loss of the nanocomposites mainly comes from CoFe₂@SWCNTs.The magnetic loss occurs mainly due to the outstanding magnetic properties of the BaFe₁₂O₁₉ ferrite,including natural ferromagnetic resonance and exchange resonance.Meanwhile,the interaction of BaFe₁₂O₁₉ nanoparticles and CoFe₂@SWCNTs also contributes to the magnetic loss.Microwave absorbing properties of the CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposites were predicted by theoretical calculation.The experimental results indicate that the impedance of the single Ba Fe₁₂O₁₉ was unmatched,so its microwave absorbing performance is poor.The impedance matching performance of nanocomposites can be improved by adjusting the proportion of the two components.Compared to single CoFe₂@SWCNTs or BaFe₁₂O₁₉ samples,the microwave absorbing properties of the nanocomposites were enhanced,due to the improvement of the impedance matching and loss mechanisms.The minimum RL-54.1 d B was observed at 11.8 GHz for the nanocomposite（5 wt.%CoFe₂@SWCNTs）with a thickness of 2.8 mm,3.4 times greater than those without CoFe₂@SWCNTs,and a broad absorption bandwidth of4.7 GHz（9.4-14.1 GHz）was achieved.In addition,the nanocomposite（1 wt.%CoFe₂@SWCNTs）shows a broader effective microwave absorption bandwidth of 7.1GHz（10.0-17.1 GHz）with a thickness of 1.9 mm.