Lightweight and high-toughness carbon fiber/phenolic ablator(CFPA)is required as the Thermal Protection System(TPS)material of aerospace vehicles for next-generation space missions.To improve the ablative properties,s...Lightweight and high-toughness carbon fiber/phenolic ablator(CFPA)is required as the Thermal Protection System(TPS)material of aerospace vehicles for next-generation space missions.To improve the ablative properties,silica sol with good particle size distribution prepared using tetramethoxysilane(TMOS)was blended with natural rubber latex and deposited onto carbon fiber felt,which was then integrated with phenolic aerogel matrix,introducing nano-silica into the framework of CFPA.The modified CFPA with a low density of 0.28—0.31 g/cm3exhibits strain-in-fracture as high as 31.2%and thermal conductivity as low as 0.054 W/(m·K).Furthermore,a trace amount of nano-silica could effectively protect CFPA from erosion of oxidizing atmosphere in different high-temperature environments.The oxyacetylene ablation test of 3000°C for 20 s shows a mass ablation rate of 0.0225 g/s,a linear ablation rate of 0.209 mm/s for the modified CFPA,which are 9.64%and 24.82%lower than the unmodified one.Besides,the long-time butane ablation test of 1200°C for 200 s shows an insignificant recession with mass and linear ablation rate of 0.079 g/s and 0.039 mm/s,16.84%and 13.33%lower than the unmodified one.Meanwhile,the fixed thermocouple in the test also demonstrates a good thermal insulation performance with a low peak back-face temperature of 207.7°C,12.25%lower than the unmodified one.Therefore,the nano-silica modified CFPA with excellent overall performance presents promising prospects in high-temperature aerospace applications.展开更多
Nonlinear electrically conductive composites are widely used for electric field grading in HVDC systems. However, the composites prepared using current methods can rarely simultaneously meet the requirements of a high...Nonlinear electrically conductive composites are widely used for electric field grading in HVDC systems. However, the composites prepared using current methods can rarely simultaneously meet the requirements of a high nonlinear coefficient, low switching field and low filler content, which limits their application scope. In this study, by applying a 10-kHz AC electric field during preparation, the prepared tetra-needle-shaped ZnO whisker/carbon fiberlliquid silicone rubber (T-ZnOw/CFILSR) composites can be implemented in a manner to meet the above three requirements. The electric field-assisted LSR composites filled with 20 phr T-ZnOw and 5 phr CF can have a switching field as low as 420 V /mm and a nonlinear coefficient up to 11.7. The mechanism for the electric field-assisted enhancement of the nonlinear characteristics of the T-ZnOw/CFILSR ternary hybrid system is explained based on the electromechanics of the suspended particles. The nonlinear characteristics and the filler content do not present a positive correlation, and a low (< 10 phr) or high (> 30 phr) filler content leads to decreased nonlinear characteristics in the composites. Compared with LSR, the electric field-assisted composites introduce a large number of shallow traps with increased trap density and reduced trap energy levels.展开更多
Carbon-based metal-free catalysts are a promising substitute for the rare and expensive platinum （Pt） used in the oxygen reduction reaction. We herein report N-doped graphene （NG） that is exquisitely integrated in...Carbon-based metal-free catalysts are a promising substitute for the rare and expensive platinum （Pt） used in the oxygen reduction reaction. We herein report N-doped graphene （NG） that is exquisitely integrated into highly conductive frameworks, simultaneously providing more active sites and higher conductivity. The NG was in situ grown on carbon fibers derived from silk cocoon （SCCf） using a simple one-step thermal treatment. The resulting product （NG-SCCf）, possessing a meso-/macroporous structure with three-dimensional （3D） interconnected networks, exhibits an onset potential that is only 0.1 V less negative than that of Pt/C and shows stability and methanol tolerance superior to those of Pt/C in alkaline media. Moreover, in the absence of Pt as co-catalyst, NG-SCCf shows a photocatalytic H2 production rate of 66.0 ~tmol-h l.g 1, 4.4-fold higher than that of SCCf. This outstanding activity is intimately related to the in situ grown NG, hierarchically porous structure, and 3D interconnected networks, which not only introduce more active sites but also enable smooth electron transfer, mass transport, and effective separation of electron-hole pairs. Considering the abundance of the green raw material in combination with easy and low-cost preparation, this work contributes to the development of advanced sustainable catalysts in energy storage/conversion fields, such as electro- and photocatalysis.展开更多
基金partly supported by the National Natural Science Foundation of China(Grant Nos.22178107,U21A2060,22178116)Xinjiang Uygur Autonomous Region Key Research and Development Program(Grant No.2022B01030)Shanghai Pujiang Program(Grant No.21PJD019)。
文摘Lightweight and high-toughness carbon fiber/phenolic ablator(CFPA)is required as the Thermal Protection System(TPS)material of aerospace vehicles for next-generation space missions.To improve the ablative properties,silica sol with good particle size distribution prepared using tetramethoxysilane(TMOS)was blended with natural rubber latex and deposited onto carbon fiber felt,which was then integrated with phenolic aerogel matrix,introducing nano-silica into the framework of CFPA.The modified CFPA with a low density of 0.28—0.31 g/cm3exhibits strain-in-fracture as high as 31.2%and thermal conductivity as low as 0.054 W/(m·K).Furthermore,a trace amount of nano-silica could effectively protect CFPA from erosion of oxidizing atmosphere in different high-temperature environments.The oxyacetylene ablation test of 3000°C for 20 s shows a mass ablation rate of 0.0225 g/s,a linear ablation rate of 0.209 mm/s for the modified CFPA,which are 9.64%and 24.82%lower than the unmodified one.Besides,the long-time butane ablation test of 1200°C for 200 s shows an insignificant recession with mass and linear ablation rate of 0.079 g/s and 0.039 mm/s,16.84%and 13.33%lower than the unmodified one.Meanwhile,the fixed thermocouple in the test also demonstrates a good thermal insulation performance with a low peak back-face temperature of 207.7°C,12.25%lower than the unmodified one.Therefore,the nano-silica modified CFPA with excellent overall performance presents promising prospects in high-temperature aerospace applications.
基金supported by the National Natural Science Foundation of China(51477085,51477086)the Shenzhen Fundamental Research and Discipline Layout Project(JCYJ20180508152044145)。
文摘Nonlinear electrically conductive composites are widely used for electric field grading in HVDC systems. However, the composites prepared using current methods can rarely simultaneously meet the requirements of a high nonlinear coefficient, low switching field and low filler content, which limits their application scope. In this study, by applying a 10-kHz AC electric field during preparation, the prepared tetra-needle-shaped ZnO whisker/carbon fiberlliquid silicone rubber (T-ZnOw/CFILSR) composites can be implemented in a manner to meet the above three requirements. The electric field-assisted LSR composites filled with 20 phr T-ZnOw and 5 phr CF can have a switching field as low as 420 V /mm and a nonlinear coefficient up to 11.7. The mechanism for the electric field-assisted enhancement of the nonlinear characteristics of the T-ZnOw/CFILSR ternary hybrid system is explained based on the electromechanics of the suspended particles. The nonlinear characteristics and the filler content do not present a positive correlation, and a low (< 10 phr) or high (> 30 phr) filler content leads to decreased nonlinear characteristics in the composites. Compared with LSR, the electric field-assisted composites introduce a large number of shallow traps with increased trap density and reduced trap energy levels.
基金The work was financially supported by National Natural Science Foundation of China （Nos. 51203182 and 51173202）, Foundation for the Author of Excellent Doctoral Dissertation of Hunan Province （No. YB2014B004）, Aeronautical Science Foundation of China （No. 20143188004）, Key Laboratory of Advanced Textile Materials and Manufacturing Technology （Zhejiang Sci-Tech University）, Ministry of Education （No. 2015001）, Key Laboratory of Lightweight and Reliability Technology for Engineering Vehicle, College of Hunan Province （No. 2016kfjj01）, Research Project of NUDT. We thank Tengyuan Wang for help in ORR experiment and helpful discussions.
文摘Carbon-based metal-free catalysts are a promising substitute for the rare and expensive platinum （Pt） used in the oxygen reduction reaction. We herein report N-doped graphene （NG） that is exquisitely integrated into highly conductive frameworks, simultaneously providing more active sites and higher conductivity. The NG was in situ grown on carbon fibers derived from silk cocoon （SCCf） using a simple one-step thermal treatment. The resulting product （NG-SCCf）, possessing a meso-/macroporous structure with three-dimensional （3D） interconnected networks, exhibits an onset potential that is only 0.1 V less negative than that of Pt/C and shows stability and methanol tolerance superior to those of Pt/C in alkaline media. Moreover, in the absence of Pt as co-catalyst, NG-SCCf shows a photocatalytic H2 production rate of 66.0 ~tmol-h l.g 1, 4.4-fold higher than that of SCCf. This outstanding activity is intimately related to the in situ grown NG, hierarchically porous structure, and 3D interconnected networks, which not only introduce more active sites but also enable smooth electron transfer, mass transport, and effective separation of electron-hole pairs. Considering the abundance of the green raw material in combination with easy and low-cost preparation, this work contributes to the development of advanced sustainable catalysts in energy storage/conversion fields, such as electro- and photocatalysis.
