硅硼碳氮陶瓷前驱体聚硼硅氮烷的合成与表征

以三氯化硼(BCl3)、三氯硅烷(HSiCl3)和六甲基二硅氮烷(Me6Si2NH)为原料,通过聚合物前驱体转化陶瓷(polymer-derived ceramics,PDCs)法成功合成了硅硼碳氮(SiBNC)陶瓷前驱体--聚硼硅氮烷(PBSZ)。采用傅里叶变换红外光谱、核磁共振、X射线光电子能谱、热重分析和差示扫描量热对PBSZ的结构和热性能进行分析。结果表明,PBSZ结构中存在硅氮硼(Si—N—B)网络和六元硼氮(B—N)环。在氮气中,800℃时PBSZ的陶瓷产率为53.9%。

Organosilicon polymer-derived ceramics: An overview

Polymer-derived ceramics(PDCs) strategy shows a great deal of advantages for the fabrication of advanced ceramics. Organosilicon polymers facilitate the shaping process and different silicon-based ceramics with controllable components can be fabricated by modifying organosilicon polymers or adding fillers. It is worth noting that silicate ceramics can also be fabricated from organosilicon polymers by the introduction of active fillers, which could react with the produced silica during pyrolysis. The organosilicon polymer-derived ceramics show many unique properties, which have attracted many attentions in various fields. This review summarizes the typical organosilicon polymers and the processing of organosilicon polymers to fabricate silicon-based ceramics, especially highlights the three-dimensional(3 D) printing technique for shaping the organosilicon polymerderived ceramics, which makes the possibility to fabricate silicon-based ceramics with complex structure. More importantly, the recent studies on fabricating typical non-oxide and silicate ceramics derived from organosilicon polymers and their biomedical applications are highlighted.

Role of in-situ formed free carbon on electromagnetic absorption properties of polymer-derived SiC ceramics

In order to enhance dielectric properties of polymer-derived SiC ceramics,a novel single-source-precursor was synthesized by the reaction of an allylhydrido polycarbosilane(AHPCS)and divinyl benzene(DVB)to form carbon-rich SiC.As expected,the free carbon contents of resultant SiC ceramics annealed at 1600℃are significantly enhanced from 6.62 wt%to 44.67 wt%.After annealing at 900-1600℃,the obtained carbon-rich SiC ceramics undergo phase separation from amorphous to crystalline feature where superfine SiC nanocrystals and turbostratic carbon networks are dispersed in an amorphous SiC(O)matrix.The dielectric properties and electromagnetic(EM)absorption performance of as-synthesized carbon-rich SiC ceramics are significantly improved by increasing the structural order and content of free carbon.For the 1600℃ ceramics mixed with paraffin wax,the minimum reflection coefficient(RCmin)reaches-56.8 dB at 15.2 GHz with the thickness of 1.51 mm and a relatively broad effective bandwidth(the bandwidth of RC values lower than-10 dB)of 4.43 GHz,indicating the excellent EM absorption performance.The carbon-rich SiC ceramics have to be considered as harsh environmental EM absorbers with excellent chemical stability,high temperature,and oxidation and corrosion resistance.

Si-based polymer-derived ceramics for energy conversion and storage

Since the 1960s,a new class of Si-based advanced ceramics called polymer-derived ceramics(PDCs)has been widely reported because of their unique capabilities to produce various ceramic materials(e.g.,ceramic fibers,ceramic matrix composites,foams,films,and coatings)and their versatile applications.Particularly,due to their promising structural and functional properties for energy conversion and storage,the applications of PDCs in these fields have attracted much attention in recent years.This review highlights the recent progress in the PDC field with the focus on energy conversion and storage applications.Firstly,a brief introduction of the Si-based polymer-derived ceramics in terms of synthesis,processing,and microstructure characterization is provided,followed by a summary of PDCs used in energy conversion systems(mainly in gas turbine engines),including fundamentals and material issues,ceramic matrix composites,ceramic fibers,thermal and environmental barrier coatings,as well as high-temperature sensors.Subsequently,applications of PDCs in the field of energy storage are reviewed with a strong focus on anode materials for lithium and sodium ion batteries.The possible applications of the PDCs in Li–S batteries,supercapacitors,and fuel cells are discussed as well.Finally,a summary of the reported applications and perspectives for future research with PDCs are presented.

Single-source-precursor derived Sioc ceramics with in-situ formed CNTs and core-shell structured CoSi@C nanoparticles towards excellent electromagnetic wave absorption properties

In this work,novel carbon nanotube(CNT)/CoSi/SiOC nanocomposite ceramics with in-situ formed multi-walled CNTs and core-shell structured CoSi@C nanoparticles were successfully prepared via a single-source-precursor derived ceramic approach.Ppolymericprecursor characterization as well as phase evolution,microstructure,and electromagnetic wave(EMW)absorption properties of the ceramics were investigated in detail.The results show that the in-situ formed CNTs and magnetic CoSi@C nanoparticles provide a synergistic effect on both dielectric loss(tand:)and magnetic loss,leading to outstanding EMW absorption properties of the ceramics annealed at only 1100 C.(i)For the Co feeding of 6.25 wt%,the minimum reflection loss(RLmin)is-53.1 dB,and the effective absorption bandwidth(EAB)is 4.96 GHz(7.12-12.08 GHz)with a ceramic-paraffin hybrid sample thickness of 3.10 mm,achieving full X-band coverage;(i)for the Co feeding of 9.09 wt%,the RLmin value of-66.4 dB and the EAB value of 3.04 GHz(8.40-11.44 GHz)were achieved with a thickness of only 2.27 mm.Therefore,the present CNT/CoSi/SiOC nanocomposite ceramics have potential applications for thin,lightweight,and efficient EMW absorption in harsh environments.

Polymer-derived SiBCN ceramic pressure sensor with excellent sensing performance

Pressure measurement with excellent stability and long time durability is highly desired,especially at high temperature and harsh environments.A polymer-derived silicoboron carbonitride(SiBCN)ceramic pressure sensor with excellent stability,accuracy,and repeatability is designed based on the giant piezoresistivity of SiBCN ceramics.The SiBCN ceramic sensor was packaged in a stainless steel case and tested using half Wheatstone bridge with the uniaxial pressure up to 10 MPa.The SiBCN ceramic showed a remarkable piezoresistive effect with the gauge factor(K)as high as 5500.The output voltage of packed SiBCN ceramic sensor changes monotonically and smoothly versus external pressure.The as received SiBCN pressure sensor possesses features of short response time,excellent repeatability,stability,sensitivity,and accuracy.Taking the excellent high temperature thermo-mechanical properties of polymer-derived SiBCN ceramics(e.g.,high temperature stability,oxidation/corrosion resistance)into account,SiBCN ceramic sensor has significant potential for pressure measurement at high temperature and harsh environments.

Formation of nanocrystalline graphite in polymer-derived SiCN by polymer infiltration and pyrolysis at a low temperature

The microstructure of polymer-derived ceramics(PDCs)was closely related to processing.This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis(PIP)at 900℃ inside a Si_(3)N_(4) whisker(Si_(3)N_(4w))preform with submicro-sized pores differed from its powder-consolidated analogue in both the content and structure of free carbon.Chemical analysis showed that PIP process had a higher free carbon yield.Raman spectroscopy and transmission electron microscopy(TEM)observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix.Dielectric properties of Si_(3)N_(4w)/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5%due to dielectric percolation caused by highly-lossy free carbon.Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si_(3)N_(4) whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

Microstructural evolution and electromagnetic wave absorbing performance of single-source-precursor-synthesized SiCuCN-based ceramic nanocomposites

Copper(Cu)-containing single-source precursors(SSPs)for the preparation of SiCuCN-based ceramic nanocomposites were successfully synthesized for the first time using polysilazane(PSZ),copper(II)acetate monohydrate(CuAc),and 2-aminoethanol via nucleophilic substitution reactions at silicon(Si)centers of PSZ.The synthesis process,polymer-to-ceramic transformation,and high-temperature microstructural evolution of the prepared ceramics were characterized.Dielectric properties and electromagnetic wave(EMW)absorbing performance of the ceramics were investigated as well.The results show that the polymer-to-ceramic transformation finishes at ca.900 ℃,and Cu nanoparticles are homogeneously distributed in a SiCN matrix,forming a SiCN/Cu nanocomposite.After annealing at 1200 ℃,the Cu nanoparticles completely transform into copper silicide(CusSi).Interestingly,the thermal stability of the Cu nanoparticles can be strongly improved by increasing the free carbon content,so that a part of metallic Cu nanoparticles can be detected in the ceramics annealed even at 1300 ℃,forming a SiCN/Cu/Cu_(3)Si/C nanocomposite.Compared with SiCN,the SiCuCN-based nanocomposites exhibit strongly enhanced dielectric properties,which results in outstanding EMW absorbing performance.The minimum reflection coefficient(RC_(min))of the SiCN/Cu/Cu_(3)Si/C nanocomposites annealed at 1300 ℃ achieves-59.85 dB with a sample thickness of 1.55 mm,and the effective absorption bandwidth(EAB)broadens to 5.55 GHz at 1.45 mm.The enhanced EMW absorbing performance can be attributed to an in situ formed unique network,which was constructed with Cu and Cu_(3)Si nanoparticles connected by ring-like carbon ribbons within the SiCN matrix.

Boron-modified perhydropolysilazane towards facile synthesis of amorphous SiBN ceramic with excellent thermal stability

SiBN ceramics are widely considered to be the most promising material for microwavetransparent applications in harsh environments owing to its excellent thermal stability and low dielectric constant.This work focuses on the synthesis and ceramization of single-source precursors for the preparation of SiBN ceramics as well as the investigation of the corresponding microstructural evolution at high temperatures including molecular dynamic simulations.Carbon-and chlorine-free perhydropolysilazanes were reacted with borane dimethyl sulfide complex at different molar ratios to synthesize single-source precursors,which were subsequently pyrolyzed and annealed under N2 atmosphere(without ammonolysis)to prepare SiBN ceramics at 1100,1200,and 1300℃with high ceramic yield in contrast to previously widely-used ammonolysis synthesis process.The obtained amorphous SiBN ceramics were shown to have remarkably improved thermal stability and oxidation resistance compared to amorphous silicon nitride.Particularly,the experimental results have been combined with molecular dynamics simulation to further study the amorphous structure of SiBN and the atomic-scale diffusion behavior of Si,B,and N at 1300℃.Incorporation of boron into the Si–N network is found to suppress the crystallization of the formed amorphous silicon nitride and hence improves its thermal stability in N2 atmosphere.