Considering the challenge of aerodynamic heating,the development of high-performance insulating ce-ramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehi-cles to achiev...Considering the challenge of aerodynamic heating,the development of high-performance insulating ce-ramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehi-cles to achieve flight at high speed for a long time.In this work,macro-porous silicon oxycarbide(SiOC)ceramics with directional pores(DP-SiOC)(mean pore size of 88.1μm)were prepared using polysiloxane precursors via freeze casting and photocrosslinking,followed by pyrolysis.The DP-SiOC samples were lightweight(density∼0.135 g cm^(-3))with a porosity of 90.4%,which showed good shapability through the molding of polysiloxane precursors.The DP-SiOC samples also exhibited an ultra-low thermal con-ductivity of 0.048 W(m K)^(-1)at room temperature,which can also withstand heat treatment at 1200°C for 1 h.In addition,scaffolds with triply periodic minimal surfaces(TPMS)were fabricated using digital light processing(DLP)printing,which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC.The TPMS scaffolds filled with macro-porous SiOC ceramics(TPMS-DP-SiOC)showed good integration between TPMS and macro-pore structures,which had a porosity∼75%and high specific strength of 9.73×10^(3)N m kg^(-1).The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)^(-1)at room temperature.The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.展开更多
Using chitin as the templating material,we obtained layered nanocomposites like shrimp or crab shells via a sol-gel self-assembly process.SEM images show a layered structure and XRD patterns present a typical peak of ...Using chitin as the templating material,we obtained layered nanocomposites like shrimp or crab shells via a sol-gel self-assembly process.SEM images show a layered structure and XRD patterns present a typical peak of chitin,which indicates the templating role of chitin in the as-received hybrid samples.Additionally,the layer spacing of chitin/silica hybrid materials is reduced with increasing content of silica.After the heat treatment for carbonization,layered SiOC nanocomposites with mesoporous structures were obtained and showed good dye adsorption performance.The present study demonstrates a reliable and self-assembly synthesis technique for the development of advanced high-performance nanocomposites with biomimetic nanostructures.展开更多
Based on the chemical cross-linking method,this paper uses polydimethylsiloxane with various viscosities of 10 cSt,20 cSt,50 cSt,and 100 cSt to synthesize mesoporous and macroporous SiOC ceramics.Their thermal conduct...Based on the chemical cross-linking method,this paper uses polydimethylsiloxane with various viscosities of 10 cSt,20 cSt,50 cSt,and 100 cSt to synthesize mesoporous and macroporous SiOC ceramics.Their thermal conductivities are measured by using 3ωmethod with high accuracy.Three typical models for their thermal conductivities,i.e.,series model(SM),maxwell-Eucken 1 model(ME1),and effective medium theory(EMT)model,are utilized to derive the empirical formula through the multi-parameter linear optimization algorithm,which agrees well with the experimental results.The effects of pore size and specific surface area on the overall thermal conductivity of the porous structure are explored.Interestingly,it is found that the thermal conductivities of both gas phase and solid phase inside the porous structure increase with the increasing pore size at the nanometer scale,but the overall thermal conductivity of the porous structure decreases with the increasing pore size.Scanning electron microscopy graphs corroborate that the extension of the heat transfer route and the barrier of more pores between the solid phases together cause the reduction of the gas-solid coupling thermal conductivity of SiOC ceramics with larger pore size.On the contrary,the miniaturization of individual particles through modulating the synthesis parameters can increase the number of small pores in the sample itself to meet the pseudo-lattice vibration conditions,which results in the increment of the gas-solid coupling thermal conductivity and the overall thermal conductivity of the porous structure.These findings would provide meaningful guidance for designing SiOC porous ceramic super-insulation materials with extremely low thermal conductivity.展开更多
In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of pr...In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of preceramic polymers,geopolymers,and sol-gel solutions.We mainly focus on processing with liquid feedstocks because they have some advantages with respect to slurry-based feedstocks in which powders are present.Particularly,lower viscosity,enhanced transparency,and lack of scattering and sedimentation are advantageous features for vat photopolymerization processes,whereas the absence of particulates reduces clogging problems at the nozzle for extrusion-based processes.Simultaneously,preceramic polymers and geopolymers have some limitations in terms of the range of ceramic compositions that can be obtained;sol-gel solutions are intrinsically unstable,whereas printed objects suffer from drying issues.Nevertheless,we successfully produced high-quality parts using a variety of additive manufacturing techniques,some of which(e.g.,volumetric additive manufacturing)have been proposed for the fabrication of ceramic components for the first time.展开更多
基金supported by the CAS Interdisciplinary Innova-tion Team Project(No.JCTD-2020-10)of the Chinese Academy of SciencesChina and the Defense Industrial Technology Develop-ment Program(No.JCKY2021130B039).
文摘Considering the challenge of aerodynamic heating,the development of high-performance insulating ce-ramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehi-cles to achieve flight at high speed for a long time.In this work,macro-porous silicon oxycarbide(SiOC)ceramics with directional pores(DP-SiOC)(mean pore size of 88.1μm)were prepared using polysiloxane precursors via freeze casting and photocrosslinking,followed by pyrolysis.The DP-SiOC samples were lightweight(density∼0.135 g cm^(-3))with a porosity of 90.4%,which showed good shapability through the molding of polysiloxane precursors.The DP-SiOC samples also exhibited an ultra-low thermal con-ductivity of 0.048 W(m K)^(-1)at room temperature,which can also withstand heat treatment at 1200°C for 1 h.In addition,scaffolds with triply periodic minimal surfaces(TPMS)were fabricated using digital light processing(DLP)printing,which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC.The TPMS scaffolds filled with macro-porous SiOC ceramics(TPMS-DP-SiOC)showed good integration between TPMS and macro-pore structures,which had a porosity∼75%and high specific strength of 9.73×10^(3)N m kg^(-1).The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)^(-1)at room temperature.The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.
基金by the Opening Funding of the State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(P2020-010)the National Natural Science Foundation of China(Nos.51521001 and 51832003)。
文摘Using chitin as the templating material,we obtained layered nanocomposites like shrimp or crab shells via a sol-gel self-assembly process.SEM images show a layered structure and XRD patterns present a typical peak of chitin,which indicates the templating role of chitin in the as-received hybrid samples.Additionally,the layer spacing of chitin/silica hybrid materials is reduced with increasing content of silica.After the heat treatment for carbonization,layered SiOC nanocomposites with mesoporous structures were obtained and showed good dye adsorption performance.The present study demonstrates a reliable and self-assembly synthesis technique for the development of advanced high-performance nanocomposites with biomimetic nanostructures.
基金This work is financially supported by Beijing Natural Science Foundation(3202020)National Natural Science Foundation of China(No.51876008)+2 种基金Beijing Nova Program(Z201100006820065)Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(FRF-IDRY-19-004)WU Jin acknowledgesfinancial support from Guangdong Natural Science Funds Grant(2018A030313400).
文摘Based on the chemical cross-linking method,this paper uses polydimethylsiloxane with various viscosities of 10 cSt,20 cSt,50 cSt,and 100 cSt to synthesize mesoporous and macroporous SiOC ceramics.Their thermal conductivities are measured by using 3ωmethod with high accuracy.Three typical models for their thermal conductivities,i.e.,series model(SM),maxwell-Eucken 1 model(ME1),and effective medium theory(EMT)model,are utilized to derive the empirical formula through the multi-parameter linear optimization algorithm,which agrees well with the experimental results.The effects of pore size and specific surface area on the overall thermal conductivity of the porous structure are explored.Interestingly,it is found that the thermal conductivities of both gas phase and solid phase inside the porous structure increase with the increasing pore size at the nanometer scale,but the overall thermal conductivity of the porous structure decreases with the increasing pore size.Scanning electron microscopy graphs corroborate that the extension of the heat transfer route and the barrier of more pores between the solid phases together cause the reduction of the gas-solid coupling thermal conductivity of SiOC ceramics with larger pore size.On the contrary,the miniaturization of individual particles through modulating the synthesis parameters can increase the number of small pores in the sample itself to meet the pseudo-lattice vibration conditions,which results in the increment of the gas-solid coupling thermal conductivity and the overall thermal conductivity of the porous structure.These findings would provide meaningful guidance for designing SiOC porous ceramic super-insulation materials with extremely low thermal conductivity.
基金support from the China Scholarship Council(Grant No.201804910741).Y.Feng acknowledges the support from the China Scholarship Council(Grant No.201806220175).
文摘In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of preceramic polymers,geopolymers,and sol-gel solutions.We mainly focus on processing with liquid feedstocks because they have some advantages with respect to slurry-based feedstocks in which powders are present.Particularly,lower viscosity,enhanced transparency,and lack of scattering and sedimentation are advantageous features for vat photopolymerization processes,whereas the absence of particulates reduces clogging problems at the nozzle for extrusion-based processes.Simultaneously,preceramic polymers and geopolymers have some limitations in terms of the range of ceramic compositions that can be obtained;sol-gel solutions are intrinsically unstable,whereas printed objects suffer from drying issues.Nevertheless,we successfully produced high-quality parts using a variety of additive manufacturing techniques,some of which(e.g.,volumetric additive manufacturing)have been proposed for the fabrication of ceramic components for the first time.
