Preparation And Microwave Absorption Of Magnetical Particles/nitrogen-doped Carbon Nanotubes

As developing of electronic and communication technology,the elec-tromagnetic compatibility becomes a crucial problem to be solved.The mi-crowave absorbers(MAs),as a proper candidates,have been used not only in military applications,like aircrafts stealing,but also in civil applications.The carbon nanotubes(CNTs)based polymer composite have attracted more and more attentions since it is light but strong.One problem for the CNTs used as the MAs is that the CNT bundle together too much which makes it diffi-cult to disperse the CNTs into a matrix.So a sophisticate pretreatment must be done to the as-prepared CNTs.These pretreatments are time-costing and increase cost which are not in favor of the large-scale production.In recent years,the Nitrogen-doped nanotubes(NCNTs)with different physical and chemical properties have attracted more attention of numerous researchers due to the applications in many areas.Nevertheless,no research has been carried out on the microwave absorption properties of the NCNTs.By doping nitrogen,the electrical properties of nanotubes should be modified,and it is possible to achieve a potential enhanced MA.The typical way to prepare the NCNTs is the CVD method using ferrocene as the catalysts and the organics containing carbon and nitrogen,like ethanol and NH3,as the precursor.The method is complex and cannot be for the large-scale preparation.In this article,a novel method using melamine and ferric chloride to synthesis the NCNT is introduced,which is simple and high-efficient com-pared with the CVD method,and the as-prepared sample as a fine powder can be easily dispersed into the matrix.1.In Chapter 2,the preparation method has been introduced and the reac-tion principles have been analyzed.2.In Chapter 3,the general properties of the NCNTs/magnetic particles have been studied by the SEM,TEM,XRD,Raman spectroscopy,XPS and VSM.The differences between Fe,Co and Ni have been introduced.3.In Chapter 4,a systematic study has been performed on the NCNTs/Fe.the processures,like the mole ratio of the resources,the pyrolyzing tem-perature and the addition of HCl,as impactors on the properties of the NCNTs/Fe have been studied.The SEM,TEM,XRD and Mossbauer spectroscopy have been performed on the materials prepared in different procesures,the results shown significant differences:the length of the tubes increase with a higher pyrolyzing temperature and a higher content of melamine;the iron trends to exist in form of α-Fe,γ-Fe and Fe3C when the temperature and the content of melamine is higher.4.In Chapter 5,the electromagnetic properties and microwave absorption of the NCNTs/Fe have been discussed.For different synthesis processures,the composites with longer tubes has larger permittivity,and RLMax of the 2:1-700 can achieve-30.05 dB with 5.70 GHz bandwidth.For different doping ratio,the permittivity of the sample increases with a higher doping ratio,which means that the electromagnetic parameters are adjustible.By changing the doping ratio to 25%,the RLMax of 2:1-800 can achieve-59.53 dB at 14.88 GHz,which is higher than-8.25 dB at 9.58 GHz when the doping ratio is 20%.For two-layer absorber material,with a proper arrangement and thickness,the composite could show two absorption peak,which indicates the com-bination microwave absorption ability of each layer.