掺杂纳米Ti对SiBCN陶瓷结构和电磁性能的影响OA

Introduction Polymer-derived ceramics are prepared via forming precursors through the polymerization of tiny molecules and cracking at high temperatures.Compared to conventional ceramics,their advantage lies in an ability to precisely control the microstructure and crystalline phase composition through the design of the molecular structure and elemental composition of the precursor and subsequent thermal treatment,thereby producing the optimal final properties.Among these,SiBCN ceramics stand out within the polymer-derived ceramics due to their flexible molecular structure designability.This enables the in-situ formation of multi-phase synergistic loss systems incorporating SiC,BN and graphitic carbon,coupled with a unique oxidation resistance mechanism,which excel particularly within polymer-derived ceramic systems.However,SiBCN ceramics primarily exist in an amorphous state at lower temperatures(i.e.,<1400℃),thus limiting their application in electromagnetic wave absorption.The paper was to introduce Ti nanopowder during the ceramicization process to catalyze the formation of nano-dielectric crystals such as SiC,TiC,and crystalline graphite.These crystals could enhance the dielectric imaginary part of SiBCN ceramics,thereby strengthening their electromagnetic wave attenuation capabilities. Methods For the synthesis of polymer precursor,tetrahydrofuran(THF)-methylvinyl dichlorosilane and borane dimethyl sulfide complex were mixed into a three-neck flask and conducted in argon for 24 h.Also,methyl dichlorosilane and hexamethyldisilazane were introduced,and the reaction was continued at the ambient temperature for 24 h.Subsequently,the mixture was then heated from room temperature to 170℃for amide copolymerization reaction.After holding at this temperature for 3 h,vacuum distillation was performed,and filtrated for three cycles,thus producing a pale yellow polyborosilazane(PBSZ).For the synthesis of SiBCN ceramibs,polyborosilazane(PBSZ)was placed in a tube furnace and heated to 280℃for 2 h to fully cure the precursor.The cured sample was subjected to ball grinding.The resultant ground powder was mixed with Ti nanopowder at different Ti mass contents(i.e,0%,5%,10%,and 15%),and then was ground to produce different composite powders,.The composite powders were pressed into discs with the diameter of φ20 mm.The discs were heat-treated in a vertical tube furnace(i.e.,firstly heating at 800℃for 1 h,and thenheating at 1000℃for 2 h)to allow enough molecular diffusion for TiC crystal formation,resulting in SiBCN ceramics. Results and discussion The analysis of the four-component doped ceramics reveals that Ti nanoparticles doping positively affects both the phase composition and dielectric properties of SiBCN ceramics.The XRD patterns indicate that pure SiBCN ceramics remain amorphous after heat treatment at 1000℃,whereas the addition of Ti nano-particles promotes the formation of TiC crystals within the ceramics,thereby enhancing their crystalline properties.The SEM and TEM images demonstrate that varying the nano-Ti doping content alters the microstructure of SiBCN ceramics.Nano-Ti addition promotes the formation of a porous structure within the ceramics and facilitates the growth of crystals such as TiC and carbon nanotubes,enriching the phase composition of the ceramics.Varying Ti nanoparticles doping contents alters SiBCN's electromagnetic wave absorption and loss capabilities.Compared to pure SiBCN ceramics,Ti nanoparticles doping confers higher electromagnetic parameters and lower reflection loss,and 10%Ti nanoparticles-doped SiBCN exhibits the optimum electromagnetic wave absorption performance.The incorporation of Ti nanoparticles optimizes the ceramic structure,with synergistic interactions among various crystals and structural components,thus enhancing the overall performance. Conclusions This study demonstrated that doping Ti nano-particles into SiBCN ceramic could enhance the ceramic dielectric loss and impedance matching qualities.Ti nano-particles enhanced the low-temperature crystallization property of SiBCN.The crystallinity and microstructure of SiBCN ceramics could be adjusted by varying the nano-Ti doping content.The ceramics heat-treated at 1000℃could develop porous architectures,TiC,and crystalline phases such as crystalline carbon.Ti nanoparticles improved the electromagnetic wave attenuation properties of SiBCN.The formation of TiC and carbon nanotubes,along with the heterogeneous interfaces formed with the amorphous matrix,could boost the electromagnetic wave attenuation performance of SiBCN ceramics.The crystallinity of SiBCN ceramics and the presence of abundant atomic defects resulted in a significant polarization loss,thereby enhancing the ceramic's electromagnetic wave absorption capability.At Ti nanoparticles content of 10%,the RLmin value of SiBCN ceramics at 6.24 GHz achieved-44.5 dB,with an EAB as high as 3.43 GHz,indicating that adding Ti nanoparticles could effectively enhance the electromagnetic wave absorption capacity of low-temperature heat-treated SiBCN ceramics.