Polymer-derived ceramics(PDCs)method opens up new possibilities for the preparation of novel multi-phase ceramic nanocomposites owing to the molecular design of the precursors at the nanoscale level.In the current wor...Polymer-derived ceramics(PDCs)method opens up new possibilities for the preparation of novel multi-phase ceramic nanocomposites owing to the molecular design of the precursors at the nanoscale level.In the current work,ZrC coatings incorporated with polymer-derived ceramic microspheres(CMS),SiH-fOC_CMS,were deposited to enhance the ablation resistance by supersonic atmosphere plasma spraying.Upon 10.0 MW·m^(-2) plasma ablation at above 3000℃,the linear ablation rate of ZrC-SiHfOC_CMS coat-ing was reduced to 0.20μm·s^(-1),62%lower than that of the pristine ZrC coating.The improvement was ascribed to the presentence of viscous SiO_(2)/HfO_(2) molten mixed phase,rather than HfSiO4,which can ef-fectively seal pinholes and cracks.Moreover,the in-situ generated crystalline SiO_(2) had a lower oxygen diffusion rate than amorphous SiO_(2),meanwhile,m-HfO_(2) could improve the stability of SiO_(2) glassy film,thus further enhancing the ablation resistance.展开更多
A major challenge is to construct ceramic membranes with tunable structures and functions for water treatment.Herein,a novel corrosion-resistant polymer-derived silicon oxycarbide(SiOC)ceramic membrane with designed a...A major challenge is to construct ceramic membranes with tunable structures and functions for water treatment.Herein,a novel corrosion-resistant polymer-derived silicon oxycarbide(SiOC)ceramic membrane with designed architectures was fabricated by a phase separation method and was applied in organic removal via adsorption and oxidation for the first time.The pore structure of the as-prepared SiOC ceramic membranes was well controlled by changing the sintering temperature and polydimethylsiloxane content,leading to a pore size of 0.84–1.62μm and porosity of 25.0–43.8%.Corrosion resistance test results showed that the SiOC membranes sustained minimal damage during 24 h exposure to high-intensity acid–base conditions,which could be attributed to the chemical inertness of SiOC.With rhodamine 6G(R6G)as the model pollutant,the SiOC membrane demonstrated an initial eff ective removal rate of 99%via adsorption;however,the removal rate decreased as the system approached adsorption saturation.When peroxymonosulfate was added into the system,efficient and continuous degradation of R6G was observed throughout the entire period,indicating the potential of the as-prepared SiOC membrane in oxidation-related processes.Thus,this work provides new insights into the construction of novel polymer-derived ceramic membranes with well-defined structures and functions.展开更多
Multiphase polymer-derived ceramics have the advantages of thermal stability and adjustable dielectric properties,which exhibit significant potential for use in high-temperature microwave absorbing materials.Herein,Co...Multiphase polymer-derived ceramics have the advantages of thermal stability and adjustable dielectric properties,which exhibit significant potential for use in high-temperature microwave absorbing materials.Herein,Co-containing polymer-derived SiCN(Co-SiCN)ceramics were successfully synthesized by the physical mixing of zeolitic imidazolate framework(ZIF)-67 and polysilazane precursors and subsequent pyrolysis.The phase and chemical compositions,microstructures,dielectric properties,electromagnetic wave absorption(EWA)performance,and mechanism of the ceramics were investigated.The results showed that the introduction of ZIF-67 promoted the in situ formation of dielectric loss phases,including SiC nanocrystals,CoSi nanocrystals,and free carbon.The phase composition can be regulated by controlling the pyrolysis temperature to achieve ideal EWA properties.The Co-SiCN ceramic pyrolyzed at 1500℃demonstrated excellent EWA performance,with a maximum effective absorption band(EAB_(max))of 3.0 GHz at an ultralow thickness of 1.05 mm and minimum reflection loss(RL_(min))of-46.4 dB at a low frequency of 6 GHz.Compared with other reported SiCN-based ceramics containing magnetic metals,the ceramics prepared in this study stand out because of their low RL and high EAB at low thicknesses.The superior microwave absorption performance of the Co-SiCN ceramics is attributed to the heterointerface polarization,and impedance matching induced by the synergistic effects of their co-existing electromagnetic transparent/absorption phases.This study provides new insights into the development of high-performance SiCNbased microwave absorbers.展开更多
Carbon nanotubes(CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires(HfC_(NWS)) through thermal pyrolysis of Hf-containing polymer precursor.The formed HfC_(N...Carbon nanotubes(CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires(HfC_(NWS)) through thermal pyrolysis of Hf-containing polymer precursor.The formed HfC_(NWS) are distributed uniformly on the surface of the carbon fibers in carbon/carbon(C/C) composites and display perfect single crystal appearance.The pyrolysis of the Hf-containing organic precursor provides hafnium and carbon source for the growth of HfC_(NWS).The released waste gasses containing CO,CH4and CO_(2)are the main carbon source for the growth of CNTs.Specifically,the flexural strength of HfC_(NWS) reinforced carbon/carbon(HfC_(NWS)-C/C) composites is enhanced by ~105% compared with pure C/C,and the CNTs/carbon cloth also displays improved electrochemical performance with respect to capacitor applications.The present study introduces a novel sustainable and eco-friendly process related to polymer-derived ceramics to form advanced ceramic nanocomposites and proposes a deep understanding of the growth mechanism of CNTs.展开更多
Defects of polymer-derived Si-C-O fibers were intensively studied by the SEM and TEM techniques and their originations were also discussed on the basis of factors experiments.The defects were found mainly in the form ...Defects of polymer-derived Si-C-O fibers were intensively studied by the SEM and TEM techniques and their originations were also discussed on the basis of factors experiments.The defects were found mainly in the form of strumaes,pits and splits on surfaces as well as microflaw networks,porosity clusters and inclusions in the bulk.Factors experiments reveal that a nonuniform or an insufficient curing would result in larger-sized strumaes or interior microflaws.Gas evolution rates due to different firing rates have a great influence on the formation of internal microflaws or porosity clusters and some oxidation-induced pits or splits may be formed on surfaces because of a trace of oxygen or water vapor accumulated from the flowing inert atmosphere during pyrolysis.展开更多
Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core un...Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core unit with excellent high-temperature conductivity,stability,and oxidation resistance is still a challenge,especially in harsh ultra-high-temperature environments.In this study,we employed a polymer-derived ceramic approach to fabricate smooth and dense SiHfBCN ceramic coatings on YCa_(4)O(BO_(3))_(3)/BN substrate.The composition,microstructural evolution,and room-temperature and high-temperature electrical conductivity of SiHfBCN ceramic coatings were investigated to reveal the mechanism for controlling electrical conductivity.The results indicate that the electrical conductivity of the SiHfBCN ceramic coating pyrolyzed at a lower temperature of 1200℃reaches an impressive high value of 291.55 S·m^(-1) at 1200℃in argon.Importantly,the results also demonstrate that the coating has remarkable high-temperature conductivity and excellent repeatability and durability.Therefore,the typical semiconducting behavior of SiHfBCN ceramic coatings highlights their potential as thin-film electrodes for SAW high-temperature sensors in high-temperature extreme environments.展开更多
In situ temperature monitoring has become extremely imperative in high-temperature harsh environments and polymer-derived ceramics(PDCs)as sensing materials have attracted great attention.However,the stability and oxi...In situ temperature monitoring has become extremely imperative in high-temperature harsh environments and polymer-derived ceramics(PDCs)as sensing materials have attracted great attention.However,the stability and oxidation/corrosion resistance of PDCs cannot be simultaneously achieved at the moment,limiting their practical application.Herein,polymer-derived SiAlBCN ceramics were synthesized via polymer conversion method under different pyrolysis temperatures.Their microstructure evolution,high temperature sensing properties,and stability were investigated in detail.The results show that the amorphous SiAlBCN phase grows more orderly and the size of the free carbon phase enlarges with the increasing temperature.The defect concentration displays a decreasing tendency.Concurrently,the SiAlBCN ceramics as sensing materials exhibit a good temperature-resistance property from roo temperature to 1100℃.The fabricated SiAlBCN temperature sensor possesses excellent stability,repeatability,and accuracy.Moreover,SiAlBCN ceramics exhibit distinguished oxidation/corrosion resistance after 100 h treatment at 1200℃in a water/oxygen environment,which is attributed to their low corrosive rate constant(0.57 mg/(cm^(2)·h))and oxidative rate constant(3.43 mg^(2)/(cm^(4)·h)).Therefore,polymer-derived SiAlBCN ceramics as sensing materials,which possess outstanding stability and oxidation/corrosion resistance,have great potential for in-situ monitoring of extreme environmental temperatures in the future.展开更多
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 contro...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.展开更多
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...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.展开更多
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,cer...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.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
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(S...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.展开更多
High-temperature stretching plays a crucial role in enhancing the performance of fibres,while a quantitative investigation into the impacts of tension and stretching duration on the microstructure and performance of h...High-temperature stretching plays a crucial role in enhancing the performance of fibres,while a quantitative investigation into the impacts of tension and stretching duration on the microstructure and performance of hexagonal boron nitride(h-BN)fibres remains absent.In this study,to elucidate the microstructural evolution of the h-BN fibres under thermal stretching,amorphous BN fibres were heated at 2000℃under tension of 30,50,and 70 N for 1,3,and 5 h in a nitrogen atmosphere.Subsequently,the grain size,pore structure,orientation degree,microscopic morphology,and mechanical properties were analysed at room temperature.The results show that high-temperature stretching enhances the orientation degree of the BN fibres,consequently elevating Young’s modulus.The maximum orientation degree of the BN fibres was 86%,aligning with a corresponding Young’s modulus of 206 GPa.Additionally,high-temperature stretching enlarged the sizes of grains and pores,a fact substantiated by the radial cracking of the fibres upon extending thermal stretching time.Owing to the expanded pore structure of the BN fibres and the inability to form a sufficiently strong“card structure”between shorter microfibre bundles,the tensile strength of the BN fibres did not increase continually,reaching a maximum of 1.0 GPa.Microstructural observations revealed that the BN fibres,composed of highly oriented lamellar h-BN grains,tend to form radial textures under high-tensile thermal stretching and onion-skin textures under prolonged thermal stretching.These findings offer a theoretical foundation for the preparation of high-performance h-BN fibres.展开更多
The current generation of ultrahigh temperature ceramic precursors typically encounters obstacles in achieving high ceramic yields(<40 wt.%)due to the challenges in integrating significant amounts of boron,which ha...The current generation of ultrahigh temperature ceramic precursors typically encounters obstacles in achieving high ceramic yields(<40 wt.%)due to the challenges in integrating significant amounts of boron,which hampers their conversion into boride-based ultrahigh temperature ceramics.To tackle these challenges,a serious of pioneering liquid multi-component hafnium-containing ceramic SiHfCB precursors(with different Hf/Si ratios)have been developed.These novel precursors are featured with stable molec-ular structure and high ceramic yield which were successfully created through a novel one-pot polymer-ization process.They present in liquid form and their structure is characterized by C-C bonds forming its main chain with branched chains of O-Si-O,Si-O-Hf,Si-O-B,and B-O-Hf which have untapped advantages including uniform component dispersion,and excellent fluidity.The ceramic yield of SiHfCB precursor with Hf/Si of 0.2 is remarkably up to 68.6 wt.%at 1500℃,and their Hf content exceeded 50 wt.%.Of particular interest,the pyrolyzed product HfB_(2)-SiC nanopowders derived from the SiHfCB precursor with Hf/Si of 0.2,consist of nanopowders in the 40-60 nm range with a density of 5.23 g cm^(−3).Remarkably,this material demonstrates exceptional performance in ultrahigh temperature oxygen-containing environ-ments at 2500℃,showing near-zero ablation with a linear ablation rate of just 2.5×10^(−4) mm s^(−1).Post-ablation analysis of the microstructure reveals that the formation of a lava-like HfO_(2) and HfO_(2)-SiO_(2) oxide layer effectively blocks oxygen penetration and provides excellent oxidation resistance.The inno-vative SiHfCB hafnium-containing ceramic precursor offers a groundbreaking solution for the preparation of lightweight ultrahigh-temperature ceramics.This development is poised to provide robust technical support for the use of ultrahigh temperature ceramics in non-ablative thermal protective systems,partic-ularly in the construction of hypersonic vehicles,where ultrahigh temperature resilience is crucial.展开更多
Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,Si...Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,SiBCN ceramic matrix composites with excellent high-temperature wave-transparent performance were prepared through PDC method.Three hyperbranched polyborosilazanes(PBSZs)were prepared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups.The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precursor and the pyrolysis temperature.The lower the methyl number and pyrolysis temperature,the lower the dielectric constant of the polymer-derived SiBCN ceramics,which is favorable for electromagnetic wave(EMW)transmittance.The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000℃ was 90.56%at room temperature.More excitingly,the excellent wave-transparent performance was also maintained in the temperature range of 100-800℃.At the test temperature of 800℃,SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13%and 88.96%,respectively.This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.展开更多
Electromagnetic wave absorbing materials at high-temperature are urgently needed for stealth aircrafts or aero-engines worked in harsh environments.In this contribution,cobaltcontaining siliconboron carbonitride(MOF/S...Electromagnetic wave absorbing materials at high-temperature are urgently needed for stealth aircrafts or aero-engines worked in harsh environments.In this contribution,cobaltcontaining siliconboron carbonitride(MOF/SiBCN)nanomaterials were prepared by pyrolyzing metal–organic framework,i.e.cobalt 2-methylimidazole(ZIF-67),and hyperbranched polyborosilazane.The rhombic dodecahedral ZIF-67 and cobalt element promoted in situ formation of dielectric loss phases,including SiC nanocrystals,CoSi nanocrystals and turbostratic carbons.The ZIF-67/SiBCN nanomaterials showed excellent microwave absorption both at room and elevated temperature.The minimum reflection coefficient(RC_(min))was-51.6dB and effective absorption bandwidth(EAB)is 3.93GHz at room temperature.At an elevated temperature of 600℃,the RC_(min) reached-30.29 dB and EAB covered almost the whole X-band(3.95GHz,8.45–12.4GHz).The ZIF-67/SiBCN nanocomposites are promising and useful platform for microwave absorbing materials at high-temperature.It may shed light on the downstream applications in designing next generation areo-engines and stealth aircrafts.展开更多
Polymer-derived ceramic(PDC) thin films are promising wear-resistant coatings for protecting metals and carbon-carbon composites from corrosion and oxidation.However,the high pyrolysis temperature hinders the applicat...Polymer-derived ceramic(PDC) thin films are promising wear-resistant coatings for protecting metals and carbon-carbon composites from corrosion and oxidation.However,the high pyrolysis temperature hinders the applications on substrate materials with low melting points.We report a new synthesis route for PDC coatings using initiated chemical vapor deposited poly(1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane)(pV_3D_3) as the precurs or.We investigated the changes in siloxane moieties and the network topology,and proposed a three-stage mechanism for the thermal annealing process.The rise of the connectivity number for the structures obtained at increased annealing temperatures was found with strong correlation to the enhanced mechanical properties and thermal conductivity.Our PDC films obtained via annealing at 850℃ exhibit at least 14.6% higher hardness than prior reports for PDCs synthesized below 1100℃.Furthermore,thermal conductivity up to 1.02 W(mK)^(-1) was achieved at the annealing temperature as low as 700℃,which is on the same order of magnitude as PDCs obtained above 1100℃.Using minimum thermal conductivity models,we found that the thermal transport is dominated by diffusons in the films below the percolation of rigidity,while ultra-short mean-free path phonons contribute to the thermal conductivity of the films above the percolation threshold.The findings of this work provide new insights for the development of wear-resistant and thermally conductive PDC thin films for durable protection coatings.展开更多
Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infil...Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis.The nanocomposite has a dense structure without micro-cracks.The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results.The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.展开更多
The emergence of additive manufacturing(AM)enables ceramics to be fabricated with customized geometry,and polymer-derived ceramics(PDCs)has attracted growing attention owing to their irreplaceable advantages.The combi...The emergence of additive manufacturing(AM)enables ceramics to be fabricated with customized geometry,and polymer-derived ceramics(PDCs)has attracted growing attention owing to their irreplaceable advantages.The combination of 3D printing and PDCs endows the resultant ceramics with both precision and performance.However,AM of ceramics from preceramic polymers is still challenging,and insufficient investigation of functionality also limits the versatility of precursor and its derived ceramics.Herein,we propose a novel paradigm for 3D printing dense silicon carbonitride ceramic and study its electrical semiconducting properties.The formulated photosensitive precursor inks could achieve self-polymerization and cross-linking under the radiation of UV light(405 nm).The green body with intricate structures is fabricated by digital light processing(DLP).Lightweight(1.79-2.08 g cm^(-3))and low porosity(<5%)amorphous ceramics were obtained after thermal treatments.Processes of cross-linking,decomposition,and ceramization are monitored and analyzed.Furthermore,the semi-conducting behaviors of resultant ceramics are identified where the conductivity(10^(-5)-10^(-1)S m^(-1))has a monotonic correspondence with the testing temperatures(25-1000℃).The numerical relationship is fitted by exponential functions,and its conducting mechanism could be interpreted by the band tail hopping(BTH)model.This work could provide alternative solutions for the fabrication of PDCs and potentials for sensing applications.展开更多
In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymer...In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.展开更多
基金supported by the National Key R&D Program of China(No.N2022YFB3708600)the National Natural Science Foundation of China(Nos.52101098 and 52061135102)+1 种基金the Fund of Key Laboratory of National Defense Science and Technol-ogy(No.WDZC20235250505)The authors also thank the Analyti-cal&Testing Center of Northwestern Polytechnical University(No.2022T019)for the characterization.
文摘Polymer-derived ceramics(PDCs)method opens up new possibilities for the preparation of novel multi-phase ceramic nanocomposites owing to the molecular design of the precursors at the nanoscale level.In the current work,ZrC coatings incorporated with polymer-derived ceramic microspheres(CMS),SiH-fOC_CMS,were deposited to enhance the ablation resistance by supersonic atmosphere plasma spraying.Upon 10.0 MW·m^(-2) plasma ablation at above 3000℃,the linear ablation rate of ZrC-SiHfOC_CMS coat-ing was reduced to 0.20μm·s^(-1),62%lower than that of the pristine ZrC coating.The improvement was ascribed to the presentence of viscous SiO_(2)/HfO_(2) molten mixed phase,rather than HfSiO4,which can ef-fectively seal pinholes and cracks.Moreover,the in-situ generated crystalline SiO_(2) had a lower oxygen diffusion rate than amorphous SiO_(2),meanwhile,m-HfO_(2) could improve the stability of SiO_(2) glassy film,thus further enhancing the ablation resistance.
基金supported by the National Key R&D Program of China(Grant No.2021YFB3200500)Natural Science Foundation of China(Grant No.52370014)+2 种基金Ningbo 3315 plan(Grant No.2018A-03-A)Natural Science Foundation of Tianjin City(Grant No.63241631)the financial support of Joint Lab for Advanced Organosilicon Precursors with Zhejiang Xinshichen New Materials Ltd.Co.
文摘A major challenge is to construct ceramic membranes with tunable structures and functions for water treatment.Herein,a novel corrosion-resistant polymer-derived silicon oxycarbide(SiOC)ceramic membrane with designed architectures was fabricated by a phase separation method and was applied in organic removal via adsorption and oxidation for the first time.The pore structure of the as-prepared SiOC ceramic membranes was well controlled by changing the sintering temperature and polydimethylsiloxane content,leading to a pore size of 0.84–1.62μm and porosity of 25.0–43.8%.Corrosion resistance test results showed that the SiOC membranes sustained minimal damage during 24 h exposure to high-intensity acid–base conditions,which could be attributed to the chemical inertness of SiOC.With rhodamine 6G(R6G)as the model pollutant,the SiOC membrane demonstrated an initial eff ective removal rate of 99%via adsorption;however,the removal rate decreased as the system approached adsorption saturation.When peroxymonosulfate was added into the system,efficient and continuous degradation of R6G was observed throughout the entire period,indicating the potential of the as-prepared SiOC membrane in oxidation-related processes.Thus,this work provides new insights into the construction of novel polymer-derived ceramic membranes with well-defined structures and functions.
基金financially supported by the National Natural Science Foundation of China(Nos.62071239,52102361)the Natural Science Foundation of Jiangsu Province(No.BK20200827)+1 种基金the National Key Laboratory on Electromagnetic Environmental Effects and Electro-optical Engineering(No.JCKYS2022LD2)the Startup Foundation for Introducing Talent of NUIST(No.2020r025)。
文摘Multiphase polymer-derived ceramics have the advantages of thermal stability and adjustable dielectric properties,which exhibit significant potential for use in high-temperature microwave absorbing materials.Herein,Co-containing polymer-derived SiCN(Co-SiCN)ceramics were successfully synthesized by the physical mixing of zeolitic imidazolate framework(ZIF)-67 and polysilazane precursors and subsequent pyrolysis.The phase and chemical compositions,microstructures,dielectric properties,electromagnetic wave absorption(EWA)performance,and mechanism of the ceramics were investigated.The results showed that the introduction of ZIF-67 promoted the in situ formation of dielectric loss phases,including SiC nanocrystals,CoSi nanocrystals,and free carbon.The phase composition can be regulated by controlling the pyrolysis temperature to achieve ideal EWA properties.The Co-SiCN ceramic pyrolyzed at 1500℃demonstrated excellent EWA performance,with a maximum effective absorption band(EAB_(max))of 3.0 GHz at an ultralow thickness of 1.05 mm and minimum reflection loss(RL_(min))of-46.4 dB at a low frequency of 6 GHz.Compared with other reported SiCN-based ceramics containing magnetic metals,the ceramics prepared in this study stand out because of their low RL and high EAB at low thicknesses.The superior microwave absorption performance of the Co-SiCN ceramics is attributed to the heterointerface polarization,and impedance matching induced by the synergistic effects of their co-existing electromagnetic transparent/absorption phases.This study provides new insights into the development of high-performance SiCNbased microwave absorbers.
基金financial supports of this work by the National Natural Science Foundation of China(Nos.52130205,51727804,91860203,52061135102)the National Key R&D Program of China(No.2021YFA0715803)the China Scholarship Program,2020(CSC No.202006290179)。
文摘Carbon nanotubes(CNTs) are fabricated in carbon cloth by ultilizing the waste gasses when fabricating hafnium carbide nanowires(HfC_(NWS)) through thermal pyrolysis of Hf-containing polymer precursor.The formed HfC_(NWS) are distributed uniformly on the surface of the carbon fibers in carbon/carbon(C/C) composites and display perfect single crystal appearance.The pyrolysis of the Hf-containing organic precursor provides hafnium and carbon source for the growth of HfC_(NWS).The released waste gasses containing CO,CH4and CO_(2)are the main carbon source for the growth of CNTs.Specifically,the flexural strength of HfC_(NWS) reinforced carbon/carbon(HfC_(NWS)-C/C) composites is enhanced by ~105% compared with pure C/C,and the CNTs/carbon cloth also displays improved electrochemical performance with respect to capacitor applications.The present study introduces a novel sustainable and eco-friendly process related to polymer-derived ceramics to form advanced ceramic nanocomposites and proposes a deep understanding of the growth mechanism of CNTs.
文摘Defects of polymer-derived Si-C-O fibers were intensively studied by the SEM and TEM techniques and their originations were also discussed on the basis of factors experiments.The defects were found mainly in the form of strumaes,pits and splits on surfaces as well as microflaw networks,porosity clusters and inclusions in the bulk.Factors experiments reveal that a nonuniform or an insufficient curing would result in larger-sized strumaes or interior microflaws.Gas evolution rates due to different firing rates have a great influence on the formation of internal microflaws or porosity clusters and some oxidation-induced pits or splits may be formed on surfaces because of a trace of oxygen or water vapor accumulated from the flowing inert atmosphere during pyrolysis.
基金financial support from the National Natural Science Foundation of China(Nos.52072304 and 51872246)supported by the Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory.
文摘Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core unit with excellent high-temperature conductivity,stability,and oxidation resistance is still a challenge,especially in harsh ultra-high-temperature environments.In this study,we employed a polymer-derived ceramic approach to fabricate smooth and dense SiHfBCN ceramic coatings on YCa_(4)O(BO_(3))_(3)/BN substrate.The composition,microstructural evolution,and room-temperature and high-temperature electrical conductivity of SiHfBCN ceramic coatings were investigated to reveal the mechanism for controlling electrical conductivity.The results indicate that the electrical conductivity of the SiHfBCN ceramic coating pyrolyzed at a lower temperature of 1200℃reaches an impressive high value of 291.55 S·m^(-1) at 1200℃in argon.Importantly,the results also demonstrate that the coating has remarkable high-temperature conductivity and excellent repeatability and durability.Therefore,the typical semiconducting behavior of SiHfBCN ceramic coatings highlights their potential as thin-film electrodes for SAW high-temperature sensors in high-temperature extreme environments.
基金the National Key R&D Program of China(No.2021YFB3200500)the National Natural Science Foundation of China(Nos.52072344 and U1904180)+1 种基金the Excellent Young Scientists Fund of Henan Province(No.202300410369)the Henan Province University Innovation Talents Support Program(No.21HASTIT001).
文摘In situ temperature monitoring has become extremely imperative in high-temperature harsh environments and polymer-derived ceramics(PDCs)as sensing materials have attracted great attention.However,the stability and oxidation/corrosion resistance of PDCs cannot be simultaneously achieved at the moment,limiting their practical application.Herein,polymer-derived SiAlBCN ceramics were synthesized via polymer conversion method under different pyrolysis temperatures.Their microstructure evolution,high temperature sensing properties,and stability were investigated in detail.The results show that the amorphous SiAlBCN phase grows more orderly and the size of the free carbon phase enlarges with the increasing temperature.The defect concentration displays a decreasing tendency.Concurrently,the SiAlBCN ceramics as sensing materials exhibit a good temperature-resistance property from roo temperature to 1100℃.The fabricated SiAlBCN temperature sensor possesses excellent stability,repeatability,and accuracy.Moreover,SiAlBCN ceramics exhibit distinguished oxidation/corrosion resistance after 100 h treatment at 1200℃in a water/oxygen environment,which is attributed to their low corrosive rate constant(0.57 mg/(cm^(2)·h))and oxidative rate constant(3.43 mg^(2)/(cm^(4)·h)).Therefore,polymer-derived SiAlBCN ceramics as sensing materials,which possess outstanding stability and oxidation/corrosion resistance,have great potential for in-situ monitoring of extreme environmental temperatures in the future.
基金support by grants from the National Natural Science Foundation of China(Grant No.51872185)the Science and Technology Commission of Shanghai Municipality(Grant No.17060502400)the University of Shanghai for Science and Technology(Grant No.2017KJFZ010).
文摘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.
基金supported by the National Natural Science Foundation of China(No.51872246)Shenzhen Science and Technology Projects(JCYJ20180306172957494).
文摘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.
基金Zhaoju Yu thanks the National Natural Science Foundation of China(Nos.51872246 and 52061135102)for financial supportQingbo Wen thanks the National Natural Science Foundation of China(No.52102085)+3 种基金the State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China(No.621022117)Fangmu Qu acknowledges the financial support by the China Scholarship Council(CSC,No.201904910776)This review also originated from the Research Training Group at TU Darmstadt and Karlsruhe Institute of Technology(KIT)entitled“Materials Composites from Composite Materials”funded by the Deutsche Forschungsgemeinschaft(DFG,No.GRK 2561)Magdalena Graczyk-Zajac acknowledges DFG support in the frame of the project GR 4440/4-1.
文摘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.
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supported by the National Natural Science Foundation of China(Grant Nos.51632007,51872229,and 52072304)National Science and Technology Major Project(Grant No.2017-VI-0007-0077).
文摘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.
基金supported by the Key Laboratory of Science and Technology on Particle Materials(Grant No.CXJJ-21S043)the Key Laboratory of Multiphase Complex Systems(Grant No.MPCS-2021-a-02)+2 种基金the Key Research Program of the Chinese Academy of Sciences(Grant Nos.ZDRW-CN-2021-2,ZDRW-CN-2021-3)Projects of Ganjiang Innovation Academy CAS(Grant Nos.E155D001,E055A002)and the Double Thousand Plan of Jiangxi Province(Grant No.JXSQ2020105012)。
文摘High-temperature stretching plays a crucial role in enhancing the performance of fibres,while a quantitative investigation into the impacts of tension and stretching duration on the microstructure and performance of hexagonal boron nitride(h-BN)fibres remains absent.In this study,to elucidate the microstructural evolution of the h-BN fibres under thermal stretching,amorphous BN fibres were heated at 2000℃under tension of 30,50,and 70 N for 1,3,and 5 h in a nitrogen atmosphere.Subsequently,the grain size,pore structure,orientation degree,microscopic morphology,and mechanical properties were analysed at room temperature.The results show that high-temperature stretching enhances the orientation degree of the BN fibres,consequently elevating Young’s modulus.The maximum orientation degree of the BN fibres was 86%,aligning with a corresponding Young’s modulus of 206 GPa.Additionally,high-temperature stretching enlarged the sizes of grains and pores,a fact substantiated by the radial cracking of the fibres upon extending thermal stretching time.Owing to the expanded pore structure of the BN fibres and the inability to form a sufficiently strong“card structure”between shorter microfibre bundles,the tensile strength of the BN fibres did not increase continually,reaching a maximum of 1.0 GPa.Microstructural observations revealed that the BN fibres,composed of highly oriented lamellar h-BN grains,tend to form radial textures under high-tensile thermal stretching and onion-skin textures under prolonged thermal stretching.These findings offer a theoretical foundation for the preparation of high-performance h-BN fibres.
基金supported by the Key Program of the National Natural Science Foundation of China(No.52032003)the Major Program of the National Natural Science Foundation of China(No.52293372)+2 种基金the National Natural Science Foundation of China(No.51972082)the National Natural Science Foundation of China(No.52102093)the National Natural Science Foundation of China(No.52172041)and the science foundation of national key laboratory of science and technology on advanced composites in special environments.
文摘The current generation of ultrahigh temperature ceramic precursors typically encounters obstacles in achieving high ceramic yields(<40 wt.%)due to the challenges in integrating significant amounts of boron,which hampers their conversion into boride-based ultrahigh temperature ceramics.To tackle these challenges,a serious of pioneering liquid multi-component hafnium-containing ceramic SiHfCB precursors(with different Hf/Si ratios)have been developed.These novel precursors are featured with stable molec-ular structure and high ceramic yield which were successfully created through a novel one-pot polymer-ization process.They present in liquid form and their structure is characterized by C-C bonds forming its main chain with branched chains of O-Si-O,Si-O-Hf,Si-O-B,and B-O-Hf which have untapped advantages including uniform component dispersion,and excellent fluidity.The ceramic yield of SiHfCB precursor with Hf/Si of 0.2 is remarkably up to 68.6 wt.%at 1500℃,and their Hf content exceeded 50 wt.%.Of particular interest,the pyrolyzed product HfB_(2)-SiC nanopowders derived from the SiHfCB precursor with Hf/Si of 0.2,consist of nanopowders in the 40-60 nm range with a density of 5.23 g cm^(−3).Remarkably,this material demonstrates exceptional performance in ultrahigh temperature oxygen-containing environ-ments at 2500℃,showing near-zero ablation with a linear ablation rate of just 2.5×10^(−4) mm s^(−1).Post-ablation analysis of the microstructure reveals that the formation of a lava-like HfO_(2) and HfO_(2)-SiO_(2) oxide layer effectively blocks oxygen penetration and provides excellent oxidation resistance.The inno-vative SiHfCB hafnium-containing ceramic precursor offers a groundbreaking solution for the preparation of lightweight ultrahigh-temperature ceramics.This development is poised to provide robust technical support for the use of ultrahigh temperature ceramics in non-ablative thermal protective systems,partic-ularly in the construction of hypersonic vehicles,where ultrahigh temperature resilience is crucial.
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.52025034)the Na-tional Key Research and Development Program of China(No.2022YFB3807100/2022YFB3807101)+1 种基金the National Natural Sci-ence Foundation of China(No.22005039)the Polymer Elec-tromagnetic Functional Materials Innovation Team of Shaanxi San-qin Scholars.
文摘Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,SiBCN ceramic matrix composites with excellent high-temperature wave-transparent performance were prepared through PDC method.Three hyperbranched polyborosilazanes(PBSZs)were prepared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups.The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precursor and the pyrolysis temperature.The lower the methyl number and pyrolysis temperature,the lower the dielectric constant of the polymer-derived SiBCN ceramics,which is favorable for electromagnetic wave(EMW)transmittance.The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000℃ was 90.56%at room temperature.More excitingly,the excellent wave-transparent performance was also maintained in the temperature range of 100-800℃.At the test temperature of 800℃,SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13%and 88.96%,respectively.This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.
基金the grant from the National Natural Science Foundation of China(No.21875190)Innovation Team of Shaanxi Sanqin Scholars and the Natural Science Basic Research Plan for Distinguished Young Scholar in Shaanxi Province of China(No.2018JC-008)。
文摘Electromagnetic wave absorbing materials at high-temperature are urgently needed for stealth aircrafts or aero-engines worked in harsh environments.In this contribution,cobaltcontaining siliconboron carbonitride(MOF/SiBCN)nanomaterials were prepared by pyrolyzing metal–organic framework,i.e.cobalt 2-methylimidazole(ZIF-67),and hyperbranched polyborosilazane.The rhombic dodecahedral ZIF-67 and cobalt element promoted in situ formation of dielectric loss phases,including SiC nanocrystals,CoSi nanocrystals and turbostratic carbons.The ZIF-67/SiBCN nanomaterials showed excellent microwave absorption both at room and elevated temperature.The minimum reflection coefficient(RC_(min))was-51.6dB and effective absorption bandwidth(EAB)is 3.93GHz at room temperature.At an elevated temperature of 600℃,the RC_(min) reached-30.29 dB and EAB covered almost the whole X-band(3.95GHz,8.45–12.4GHz).The ZIF-67/SiBCN nanocomposites are promising and useful platform for microwave absorbing materials at high-temperature.It may shed light on the downstream applications in designing next generation areo-engines and stealth aircrafts.
基金funding from the National Natural Science Foundation of China (22178301,21938011,51876186and 52150410417)the funding from the Natural Science Foundation of Zhejiang Province (LR21B060003 and LZ19E060002)+1 种基金grant from Science Technology Department of Zhejiang Province (2023C01182)supported by Shanxi Institute of Zhejiang University for New Materials and Chemical Industry(2022SZ-TD005)。
文摘Polymer-derived ceramic(PDC) thin films are promising wear-resistant coatings for protecting metals and carbon-carbon composites from corrosion and oxidation.However,the high pyrolysis temperature hinders the applications on substrate materials with low melting points.We report a new synthesis route for PDC coatings using initiated chemical vapor deposited poly(1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane)(pV_3D_3) as the precurs or.We investigated the changes in siloxane moieties and the network topology,and proposed a three-stage mechanism for the thermal annealing process.The rise of the connectivity number for the structures obtained at increased annealing temperatures was found with strong correlation to the enhanced mechanical properties and thermal conductivity.Our PDC films obtained via annealing at 850℃ exhibit at least 14.6% higher hardness than prior reports for PDCs synthesized below 1100℃.Furthermore,thermal conductivity up to 1.02 W(mK)^(-1) was achieved at the annealing temperature as low as 700℃,which is on the same order of magnitude as PDCs obtained above 1100℃.Using minimum thermal conductivity models,we found that the thermal transport is dominated by diffusons in the films below the percolation of rigidity,while ultra-short mean-free path phonons contribute to the thermal conductivity of the films above the percolation threshold.The findings of this work provide new insights for the development of wear-resistant and thermally conductive PDC thin films for durable protection coatings.
文摘Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis.The nanocomposite has a dense structure without micro-cracks.The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results.The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.
基金the National Natural Science Foundation of China(No.12090034).
文摘The emergence of additive manufacturing(AM)enables ceramics to be fabricated with customized geometry,and polymer-derived ceramics(PDCs)has attracted growing attention owing to their irreplaceable advantages.The combination of 3D printing and PDCs endows the resultant ceramics with both precision and performance.However,AM of ceramics from preceramic polymers is still challenging,and insufficient investigation of functionality also limits the versatility of precursor and its derived ceramics.Herein,we propose a novel paradigm for 3D printing dense silicon carbonitride ceramic and study its electrical semiconducting properties.The formulated photosensitive precursor inks could achieve self-polymerization and cross-linking under the radiation of UV light(405 nm).The green body with intricate structures is fabricated by digital light processing(DLP).Lightweight(1.79-2.08 g cm^(-3))and low porosity(<5%)amorphous ceramics were obtained after thermal treatments.Processes of cross-linking,decomposition,and ceramization are monitored and analyzed.Furthermore,the semi-conducting behaviors of resultant ceramics are identified where the conductivity(10^(-5)-10^(-1)S m^(-1))has a monotonic correspondence with the testing temperatures(25-1000℃).The numerical relationship is fitted by exponential functions,and its conducting mechanism could be interpreted by the band tail hopping(BTH)model.This work could provide alternative solutions for the fabrication of PDCs and potentials for sensing applications.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.21174112 and 51242009)the Research Fund of State Key Laboratory of Solidification Processing(Grant No.82-TZ-2013)+1 种基金the project "111"(B08040)the grant of the New Century Excellent Talents of Education Ministry of China(NCET-110817)
文摘In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.
