In this study,the structural evolution of SiBCN ceramics during crystallization and its effects on oxidation behavior involving different atomic units or formed phases in amorphous or crystalline SiBCN ceramics were a...In this study,the structural evolution of SiBCN ceramics during crystallization and its effects on oxidation behavior involving different atomic units or formed phases in amorphous or crystalline SiBCN ceramics were analyzed.The amorphous structure has exceptionally high oxidation activity but presents much better oxidation resistance due to its synchronous oxidation of atomic units and homogeneous composition in the generated oxide layer.However,the oxidation resistance of SiBCN ceramic will degrade during the continual crystallization process,especially for the formation of the nanocapsule-like structure,due to heterogeneous oxidation caused by the phase separation.Besides,the activation energy and rate-controlling mechanism of the atomic units and phases in SiBCN ceramics were obtained.The BNCx(Ea=145 kJ/mol)and SiC(2-x)(Ea=364 kJ/mol)atomic units in amorphous SiBCN structure can be oxidized at relatively lower temperatures with much lower activation energy than the corresponding BN(C)(Ea=209 kJ/mol)and SiC(Ea=533 kJ/mol)phases in crystalline structure,and the synchronous oxidation of the SiC(2-x)and BNCx units above 750C changes the oxidation activation energy of BNCx(Ea=332 kJ/mol)to that similar to SiC(2-x).The heterogeneous oxide layer formed from the nanocapsule-like structure will decrease the activation energy SiC(Ea=445 kJ/mol)and t-BN(Ea=198 kJ/mol).展开更多
Porous SiBCN ceramics exhibit great potential in high-tech structural and functional applications. However, nucleation-crystallization and carbothermal decomposition limit their use in high-temperature environments. H...Porous SiBCN ceramics exhibit great potential in high-tech structural and functional applications. However, nucleation-crystallization and carbothermal decomposition limit their use in high-temperature environments. Herein, high-entropy carbide (HEC) (Ti_(0.25)Zr_(0.25)Hf_(0.25)Ta_(0.25))C-modified porous SiBCN ceramics (HEC/SiBCN) were successfully fabricated from a multi-metal (Ti,Zr,Hf,Ta) precursor containing polyborosilazane via solvothermal methods, freeze-drying, and pyrolysis. The porous HEC/SiBCN ceramic possesses tailorable porosity (63.5%–79.1%), low thermal conductivity (0.054–0.089 W/(m·K)), and good mechanical strength. The HEC phase is in situ formed by carbothermal reduction and solid solution reaction of the multicomponent precursor with highly active free carbon in the SiBCN matrix during the pyrolysis, which endows the porous HEC/SiBCN ceramics with outstanding thermal stability up to 1800℃. The in situ formation of the HEC phase provides novel insight and a promising strategy for enhancing the overall performance of porous SiBCN ceramics, expanding their application in high-temperature environments.展开更多
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 w...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.展开更多
SiBCN ceramic aerogels have emerged as a new generation of integrated thermal insulation and microwave absorption materials but face great challenges in terms of mechanical properties,high-temperature stability,and ab...SiBCN ceramic aerogels have emerged as a new generation of integrated thermal insulation and microwave absorption materials but face great challenges in terms of mechanical properties,high-temperature stability,and absorption bandwidth in practical applications.Herein,SiBCN/SiOC composite ceramic aerogels were prepared by solvent thermal crosslinking,freeze-drying,and pyrolysis of precursors.Polyhydromethylsiloxane(PHMS)was introduced in situ by the hydrosilane addition reaction during the solvothermal process,which endowed the precursor aerogel with a complex and robust three-dimensional network structure and further resulted in a 260%improvement in the compressive strength of the SiBCN/SiOC composite aerogel compared with that of the pure SiBCN aerogel.Additional investigations revealed that the SiBCN/SiOC composite aerogel enjoyed a low thermal conductivity(0.044-0.051 W·m^(-1)·K^(-1))and a light weight(0.13-0.16 g·cm^(-3)),which was favorable for thermal barrier material.Notably,the SiBCN/SiOC composite aerogel exhibited excellent microwave absorption performance with an effective absorption bandwidth of 6.7 GHz and a reflection loss of−43.89 dB at a thickness of 2.5 mm due to improved impedance matching,multiple reflections,and enhanced interfacial polarization.Furthermore,the introduction of SiOC significantly inhibited the crystallization of SiBCN at high temperatures.After heat treatment at 1600℃,the composite aerogel retained its amorphous nanoparticle pearl-chain-like structure,with thermal conductivity remaining as low as 0.052 W·m^(-1)·K^(-1).The in situ introduction of PHMS provided novel insight and a promising strategy for enhancing the overall performance of SiBCN ceramic aerogels,expanding their application in hightemperature environments.展开更多
Electromagnetic wave(EMW)absorbers with broadband attenuation and long-term stability are important for applications in marine environments.Dielectric ceramics excel in terms of thermal and chemical resistance but off...Electromagnetic wave(EMW)absorbers with broadband attenuation and long-term stability are important for applications in marine environments.Dielectric ceramics excel in terms of thermal and chemical resistance but offer limited impedance matching,whereas magnetic materials provide strong absorption but degrade rapidly due to corrosion.Herein,we present an engineering approach for polymer-derived ceramics that utilizes ferric crosslinking to integrate both magnetic functionality and hierarchical structure within a single system.By reacting iron(Ⅲ)acetylacetonate with Si–H groups in polyborosilazane,a uniformly distributed ferric polymer network is formed.Subsequent pyrolysis drives carbon nanotube growth and Fe_(x)Si_(y) phase formation,yielding a distinctive hierarchical“mushroom-like”structure composed of SiBCN matrices,carbon nanotube stems,and carbon-encapsulated Fe_(x)Si_(y) caps.This structure promotes EMW absorption via magnetodielectric synergy,rich interfaces,and multiple scattering,whereas carbon-encapsulated Fe_(x)Si_(y) in the SiBCN matrix provides corrosion resistance.The effective absorption bandwidth(EAB,defined as a reflection loss of less than-10 dB)of h-SiBCNFe reaches 8.16 GHz,while it also has a corrosion potential(E_(corr))of 0.033 V and an ultralow corrosion current(I_(corr))of 0.63μA·cm^(-2).These features highlight a new design strategy for developing advanced EMW absorbers tailored for marine applications.展开更多
In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumvent...In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumventing the challenges of sintering densification(>1800℃).Unlike the elastic fracture in over-cured precursors or the viscoelastic deformation in under-cured precursors,the partially cured precursor,exhibiting elastic-plastic deformation behavior,facilitates limited nanoscale pore formation in a dense structure,achieving a balance between crack-free pyrolysis and densification.Compared to SiBCN derived from the over-cured precursor(σ=~159 MPa,K_(IC)=1.9 MPa:m^(1/2),Vickers hardness(HV)=7.8 GPa,and E=122 GPa),the resulting SiBCN monolith exhibited significantly improved mechanical properties(σ=~304 MPa,K_(IC)=3.7 MPa-m12,HV=10.6 GPa,and E=161 GPa)and oxidation resistance.In addition,this study investigated the high-temperature performance of SiBCN monoliths,including crystallization and oxidation,and determined the oxidation kinetics induced by pore structure healing and the different oxidation mechanisms of Si-C-N and B-C-N clusters in the amorphous structure.Due to its unique composition and structure,the SiBCN ceramic oxide layer exhibits exceptional self-healing effects on repairing the nanoporous system in the initial stage and shows outstanding high-temperature stability during prolonged oxidation,mitigating adverse effects from bubble formation and crystallization.Due to the nanoporous structure,the oxidation rate is initially controlled by gas diffusion following a linear law before transitioning to oxide layer diffusion characterized by a parabolic law.Finally,due to different valence bond configurations,Si-C-N transforms into an amorphous SiCNO structure after phase separation,unlike the nucleation and growth of residual B-N-C.展开更多
To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer...To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant no.52002092,51832002,52172068,52232004,52372059)Heilong Jiang Natural Science Fund for Young Scholars(Grant no.YQ2021E017)+2 种基金National Key Research and Development Program of China(Grant no.2017YFB0310400)Heilongjiang Touyan Team Program,Advanced Talents Scientific Research Foundation of Shenzhen,and Fundamental Research Funds for the Central Universities(2022FRFK0600XX)RR gratefully acknowledges the financial support provided by the Research Training Group 2561“MatCom-ComMat:Materials Compounds from Composite Materials for Applications in Extreme Conditions”funded by the Deutsche Forschungsgemeinschaft(DFG),Bonn,Germany.
文摘In this study,the structural evolution of SiBCN ceramics during crystallization and its effects on oxidation behavior involving different atomic units or formed phases in amorphous or crystalline SiBCN ceramics were analyzed.The amorphous structure has exceptionally high oxidation activity but presents much better oxidation resistance due to its synchronous oxidation of atomic units and homogeneous composition in the generated oxide layer.However,the oxidation resistance of SiBCN ceramic will degrade during the continual crystallization process,especially for the formation of the nanocapsule-like structure,due to heterogeneous oxidation caused by the phase separation.Besides,the activation energy and rate-controlling mechanism of the atomic units and phases in SiBCN ceramics were obtained.The BNCx(Ea=145 kJ/mol)and SiC(2-x)(Ea=364 kJ/mol)atomic units in amorphous SiBCN structure can be oxidized at relatively lower temperatures with much lower activation energy than the corresponding BN(C)(Ea=209 kJ/mol)and SiC(Ea=533 kJ/mol)phases in crystalline structure,and the synchronous oxidation of the SiC(2-x)and BNCx units above 750C changes the oxidation activation energy of BNCx(Ea=332 kJ/mol)to that similar to SiC(2-x).The heterogeneous oxide layer formed from the nanocapsule-like structure will decrease the activation energy SiC(Ea=445 kJ/mol)and t-BN(Ea=198 kJ/mol).
基金supported by the National Natural Science Foundation of China(No.52173261)the Science and Technology on Advanced Functional Composites Laboratory(No.6142906240505).
文摘Porous SiBCN ceramics exhibit great potential in high-tech structural and functional applications. However, nucleation-crystallization and carbothermal decomposition limit their use in high-temperature environments. Herein, high-entropy carbide (HEC) (Ti_(0.25)Zr_(0.25)Hf_(0.25)Ta_(0.25))C-modified porous SiBCN ceramics (HEC/SiBCN) were successfully fabricated from a multi-metal (Ti,Zr,Hf,Ta) precursor containing polyborosilazane via solvothermal methods, freeze-drying, and pyrolysis. The porous HEC/SiBCN ceramic possesses tailorable porosity (63.5%–79.1%), low thermal conductivity (0.054–0.089 W/(m·K)), and good mechanical strength. The HEC phase is in situ formed by carbothermal reduction and solid solution reaction of the multicomponent precursor with highly active free carbon in the SiBCN matrix during the pyrolysis, which endows the porous HEC/SiBCN ceramics with outstanding thermal stability up to 1800℃. The in situ formation of the HEC phase provides novel insight and a promising strategy for enhancing the overall performance of porous SiBCN ceramics, expanding their application in high-temperature environments.
基金The authors appreciate the financial support from the National Natural Science Foundation of China(No.U1904180)Key Scientific Research Projects of High Education Institutions of Henan province(No.19A430025).
文摘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.
基金financially supported by the National Key R&D Program of China(No.2023YFB3711200)the National Natural Science Foundation of China(No.52572081).
文摘SiBCN ceramic aerogels have emerged as a new generation of integrated thermal insulation and microwave absorption materials but face great challenges in terms of mechanical properties,high-temperature stability,and absorption bandwidth in practical applications.Herein,SiBCN/SiOC composite ceramic aerogels were prepared by solvent thermal crosslinking,freeze-drying,and pyrolysis of precursors.Polyhydromethylsiloxane(PHMS)was introduced in situ by the hydrosilane addition reaction during the solvothermal process,which endowed the precursor aerogel with a complex and robust three-dimensional network structure and further resulted in a 260%improvement in the compressive strength of the SiBCN/SiOC composite aerogel compared with that of the pure SiBCN aerogel.Additional investigations revealed that the SiBCN/SiOC composite aerogel enjoyed a low thermal conductivity(0.044-0.051 W·m^(-1)·K^(-1))and a light weight(0.13-0.16 g·cm^(-3)),which was favorable for thermal barrier material.Notably,the SiBCN/SiOC composite aerogel exhibited excellent microwave absorption performance with an effective absorption bandwidth of 6.7 GHz and a reflection loss of−43.89 dB at a thickness of 2.5 mm due to improved impedance matching,multiple reflections,and enhanced interfacial polarization.Furthermore,the introduction of SiOC significantly inhibited the crystallization of SiBCN at high temperatures.After heat treatment at 1600℃,the composite aerogel retained its amorphous nanoparticle pearl-chain-like structure,with thermal conductivity remaining as low as 0.052 W·m^(-1)·K^(-1).The in situ introduction of PHMS provided novel insight and a promising strategy for enhancing the overall performance of SiBCN ceramic aerogels,expanding their application in hightemperature environments.
基金support from the National Science Fund for Distinguished Young Scholars(Jie Kong)(No.52025034)the Joint Funds of the National Natural Science Foundation of China(Jie Kong)(No.U24A20204)+1 种基金the National Natural Science Foundation of China(Jin Liang,Zhen Yu)(Nos.52573096 and 52503112)the Innovation Team of Shaanxi Sanqin Scholars(Jie Kong).
文摘Electromagnetic wave(EMW)absorbers with broadband attenuation and long-term stability are important for applications in marine environments.Dielectric ceramics excel in terms of thermal and chemical resistance but offer limited impedance matching,whereas magnetic materials provide strong absorption but degrade rapidly due to corrosion.Herein,we present an engineering approach for polymer-derived ceramics that utilizes ferric crosslinking to integrate both magnetic functionality and hierarchical structure within a single system.By reacting iron(Ⅲ)acetylacetonate with Si–H groups in polyborosilazane,a uniformly distributed ferric polymer network is formed.Subsequent pyrolysis drives carbon nanotube growth and Fe_(x)Si_(y) phase formation,yielding a distinctive hierarchical“mushroom-like”structure composed of SiBCN matrices,carbon nanotube stems,and carbon-encapsulated Fe_(x)Si_(y) caps.This structure promotes EMW absorption via magnetodielectric synergy,rich interfaces,and multiple scattering,whereas carbon-encapsulated Fe_(x)Si_(y) in the SiBCN matrix provides corrosion resistance.The effective absorption bandwidth(EAB,defined as a reflection loss of less than-10 dB)of h-SiBCNFe reaches 8.16 GHz,while it also has a corrosion potential(E_(corr))of 0.033 V and an ultralow corrosion current(I_(corr))of 0.63μA·cm^(-2).These features highlight a new design strategy for developing advanced EMW absorbers tailored for marine applications.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52372059,52172068,52232004,and 52002092)the Heilong Jiang Natural Science Fund for Young Scholars(No.YQ2021E017)+2 种基金the Fundamental Research Funds for the Central Universities(No.2022FRFK060012)the Heilongjiang Touyan Team Program,and the Advanced Talents Scientific Research Foundation of Shenzhen:Yu ZhouThis work was also funded by the Beijing Engineering Research Center of Efficient and Green Aerospace PropulsionTechnology and Advanced Space Propulsion Laboratory of Beijing Institute of Control Engineering(BICE)(No.LabASP-2023-11).
文摘In this study,a crack-free pyrolysis process of partially cured precursor powder compacts was developed to prepare dense silicon boron carbonitride(SiBCN)monoliths at much lower temperatures(1300℃),thereby circumventing the challenges of sintering densification(>1800℃).Unlike the elastic fracture in over-cured precursors or the viscoelastic deformation in under-cured precursors,the partially cured precursor,exhibiting elastic-plastic deformation behavior,facilitates limited nanoscale pore formation in a dense structure,achieving a balance between crack-free pyrolysis and densification.Compared to SiBCN derived from the over-cured precursor(σ=~159 MPa,K_(IC)=1.9 MPa:m^(1/2),Vickers hardness(HV)=7.8 GPa,and E=122 GPa),the resulting SiBCN monolith exhibited significantly improved mechanical properties(σ=~304 MPa,K_(IC)=3.7 MPa-m12,HV=10.6 GPa,and E=161 GPa)and oxidation resistance.In addition,this study investigated the high-temperature performance of SiBCN monoliths,including crystallization and oxidation,and determined the oxidation kinetics induced by pore structure healing and the different oxidation mechanisms of Si-C-N and B-C-N clusters in the amorphous structure.Due to its unique composition and structure,the SiBCN ceramic oxide layer exhibits exceptional self-healing effects on repairing the nanoporous system in the initial stage and shows outstanding high-temperature stability during prolonged oxidation,mitigating adverse effects from bubble formation and crystallization.Due to the nanoporous structure,the oxidation rate is initially controlled by gas diffusion following a linear law before transitioning to oxide layer diffusion characterized by a parabolic law.Finally,due to different valence bond configurations,Si-C-N transforms into an amorphous SiCNO structure after phase separation,unlike the nucleation and growth of residual B-N-C.
基金the National Natural Science Foundation of China(Nos.52372059,52172068,52232004,and 52002092)the Heilongjiang Natural Science Fund for Young Scholars(No.YQ2021E017)+3 种基金the Fundamental Research Funds for the Central Universities(No.2022FRFK060012)the Heilongjiang Touyan Team Program,and the Advanced Talents Scientific Research Foundation of Shenzhen:Yu Zhou.the Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology and Advanced Space Propulsion Laboratory of BICE(No.LabASP-2023-11)the Huiyan Action(No.1A423653)the Key Technologies R&D Program of CNBM(No.2023SJYL05).Ralf Riedel also gratefully acknowledges the financial support provided by the Research Training Group 2561“MatCom-ComMat:Materials Compounds from Composite Materials for Applications in Extreme Conditions”funded by the Deutsche Forschungsgemeinschaft(DFG),Bonn,Germany.
文摘To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.
