| Polymer-derived ceramics(PDCs),such as PDC-SiC,PDC-SiOC and PDC-SiCN ceramics,have the advantages of low density,high temperature resistance,oxidation resistance and excellent electromagnetic properties,and are considered as one of the alternatives to high temperature electromagnetic wave absorption materials.In recent years,silicon-based ceramics have received extensive attention in the field of electromagnetic wave absorption,and researchers generally adopt methods of introducing electromagnetic wave absorption phase,such as nano-carbon phase,to improve their absorption properties.However,nanophases are easy to agglomerate to reduce its conductivity and absorbing properties.The PDC route can control the phase composition and microstructure of the ceramic by the design of the precursor,and in situ form the absorption phase,such as free carbon.It is a method to effectively avoid agglomeration in traditional physical blending methods and improve the absorption properties of the ceramics.Therefore,the PDCs have a broad prospect in the field of electromagnetic wave absorption.In this article,based on the single-source-precursor route,preceramic precursor allylhydridopolycarbosilane(AHPCS),polysiloxane(PSO)and polysilazane(PSZ)were modified by divinylbenzene(DVB)which was high carbon content compound via chemical reaction,then a series of single-source-precursors were successfully synthesized.After crosslinking,pyrolysis and high temperature annealing,carbon-rich silica-based ceramics were prepared.Finally,the synthesis mechanism,phase composition,microstructure and electromagnetic and wave absorption properties were studied by various characterization methods.The main results are as follows:Firstly,AHPCS was modified by DVB to prepare single-source-precursor PAD with different carbon content,and carbon-rich SiC/C ceramics were prepared by PDC route.The study shows that the introduction of DVB significantly increases the free carbon content of ceramics,up to 44.67wt%,while that of ceramics derived from pure AHPCS is only 6.62wt%.The microstructure indicates that a large amount of free carbon distributes uniformly in matrix,forming a conductive network and improving the dielectric and absorption properties of the ceramics.The minimum reflection coefficient of ceramics is-56.8dB and the effective absorption bandwidth within the range of 2-18GHz through thickness adjustment is up to 12.8GHz.It is a potential electromagnetic wave absorption material used at high temperature.Secondly,the PSO was modified by DVB to prepare a series of single-source-precursor PSOD and the carbon-rich SiOC/C ceramics were prepared by PDC route.Result shows that the introduction of DVB reduces the ceramic yield but increases the free carbon content of ceramic,from 0.80 to 25.45wt%.After annealing at high temperature,the order of free carbon increases and constitutes a conductive network,resulting in the increase of conductive loss and interfacial polarization,which improves the dielectric and absorption properties of the ceramics?The minimum reflection coefficient of ceramics is-49.81dB.Through the thickness adjustment,the effective absorption bandwidth can reach 14.48GHz in the range of 2-18GHz.It proves that an excellent wide-band adjustable absorption material is prepared.Thirdly,a series of single-source-precursors PSZD with different carbon content were synthesized by using DVB and PSZ as raw materials and carbon-rich SiCN/C ceramics were prepared via PDC route.Research shows that the free carbon content of ceramics is significantly improved by the introduction of DVB,from 1.67 wt%(without DVB)to 39.72wt%.The free carbon gradually becomes a conductive network as the annealing temperature increasing,which leads to the improvement of the dielectric and absorption properties of ceramics.The minimum reflection coefficient of ceramics is-53.88dB and the effective absorption bandwidth can reach 14.48GHz in the range of 2-18GHz through thickness adjustment,showing excellent electromagnetic wave absorption performance. |
PDF Full Text Request