Study Of Complex Carbon-based Radar Wave Absorbers Derived From Poly (Phthalazinone Ether Nitrile Ketone) Resin

With the wide application of radar in the military field,the design and manufacture of radar wave absorption materials with light-weight,strong-absorption,broadband,and thin thickness is essential to protect our military powers.As typical resistance loss absorbers,carbon materials have advantages of comprehensive source,easy preparation,low cost,highly conductive,strong loss ability,and low density.Many nano-scale carbon materials such as carbon nanotubes and graphene have been synthesized for radar wave absorbers,but their poor surface impedance matching performance limits absorption performance.Significantly,the narrow adequate absorption bandwidth(EAB)of carbon materials at low filling ratio and low thickness(< 2.0 mm)restricts practical applications.Poly(phthalazinone ether nitrile ketone)(PPENK)resin has the potential to improve surface impedance matching performance of carbon materials because of its characteristics of high thermal stability,soluble in DMAc and chloroform,and rich nitrogen and oxygen content.Therefore,this thesis aims to prepare complex carbon-based absorbers with wide EAB at a low filling ratio and thickness using PPENK resin precursors.The relationships of chemical compositions,morphologies,and structures on radar wave absorption performance and mechanisms are investigated systematically.The main research contents are as follows.(1)PPENK resin with outstanding solubility and low dielectric constant can be a valid template to improve the surface impedance matching performance of MWCNTs.Hence,Fe3O4 nanoparticles and acid-treated multi-walled carbon nanotubes(AMWCNTs)were complexed on the surface of PPENK microspheres to prepare complex absorbers PPENK@Fe3O4/AMWCNTs via the co-precipitation method.Results show that the surface impedance matching the performance of AMWCNTs becomes better because the normalized impedance bandwidth has enlarged from 2.4 GHz to 5.3 GHz.It can be seen from the discussion that the absorption performance of sole AMWCNTs is poor because the EAB is 0 when the thickness is 3.1 mm.Meanwhile,the RLmin value is-32.6 d B(@16.98 GHz),and EAB reaches2.1 GHz(15.9~18.0 GHz)with a thickness of even 4.9 mm.The absorption performance of PPENK@Fe3O4/AMWCNTs enhances because the RL achieves the lowest value of-58.4 d B(@7.88 GHz)at 3.1 mm.The maximum EAB is 4.3 GHz(7.6~11.9 GHz)with a thickness of2.8 mm covering almost the whole X band.(2)Using Iron(III)2,4-pentanedionate and nitrogen,oxygen-rich polymer PPENK as precursors,heteroatoms-doped Fe3C@C nanofibers absorber was prepared by electrospinning and the following thermal treatment process.The morphology and composition of Fe3C@C nanofibers could be controlled by adjusting annealing temperature.The radar wave absorption properties could be adjusted simultaneously.The carbon-based nanofibers derived from PPENK have enormous nitrogen,oxygen atoms(7.9 at.%)after treatment of 700 ℃@3 h.Higher temperature treatment promotes the conversion of nitrogen atoms from pyridine-N and pyrrole-N to graphite-N and pyridine-N oxides.The ′ and ′′ values of Fe3C@C nanofibers absorber increase firstly and then decrease with the ascent of annealing temperature,while S700 holds the maximum value.S700 has the best absorption performance,and the RLmin value at8.31 GHz is-35.5 d B when the filling ratio is 30 wt.%,and the thickness is 2.8 mm.The EAB reaches 4.9 GHz(13.1~18.0 GHz)when the thickness is 1.6 mm.(3)To improve surface impedance matching performance and attenuation performance simultaneously,constructing nanoscale morphology on the skeleton of carbon-based nanofibers would reduce the filling ratio of absorbers and the thickness of absorption materials.Heteroatoms-doped Ni@C nanofibers with branch-like morphology were prepared through a two-step strategy of electrospinning and following polymer pyrolysis chemical vapor deposition(PPCVD)process,using nickel(II)acetylacetone(Ni(acac)2)and PPENK resin with high thermal stability and rich nitrogen and oxygen content.The influences of morphology and composition of complex absorbers on radar wave absorption performance were investigated by changing the addition of Ni(acac)2.PPENK resin has degraded into carbon nanofiber skeletons with high nitrogen and oxygen atom ratios,and the content of heteroatoms can be up to 8.8 at.%when the mass ratio of Ni(acac)2 and PPENK is 0.5:1(S0.5).Ni nanoparticles from Ni(acac)2catalyze the in-situ growth of MWCNTs,forming 3D branch-like structure.The distribution density and length-diameter ratio of MWCNTs present an inverted V-shaped change trend,while ′ and ′′ values show the same trends with the increasing of Ni(acac)2 content.S0.5has the maximum values of ′ and ′′,and S0.5 achieves the best radar wave absorption performance.When the filling ratio is 20 wt.% and the thickness of 1.5 mm,the RLmin value is-53.2 d B at 14.3 GHz,and EAB could reach 5.6 GHz(12.4~18.0 GHz),covering most Ku band.(4)In order to reduce the filling ratio and broaden EAB furtherly,NCNTs@PPENK precursor with porous morphology was constructed by solvent substitution method using PPENK resin and nitrogen-doped multi-walled carbon nanotubes(NCNTs)as raw materials.3D porous NCNTs@C complex absorber was prepared by annealing treatment.The porous structure and radar wave absorption performance of NCNTs@C absorber could be adjusted by controlling PPENK/chloroform solution concentration,annealing temperature,and filling ratio.PPENK resin has nucleated and solidified on the surface of NCNTs skeleton as coatings and formed porous morphology.After annealing,NCNTs@C inherits the porous morphology.Increasing the annealing temperature is beneficial to raise ′ and ′′ values of NCNTs@C absorbers.With the increasing filling ratio,the radar wave absorption performance of NC900 absorber increases firstly and then decreases.When the filling ratio is 15 wt.%,the paraffinbased NC900 absorption material achieves the best surface impedance matching performance and the strongest absorption performance.When the thickness is just 1.8 mm,the EAB is as large as 7.1 GHz(10.8-18.0 GHz),which can completely cover the Ku band.When the thickness is 2.1 mm,the RLmin value reaches-53.5 d B at 10.69 GHz.