To meet the emerging demands for thermal protection materials for hypersonic aircraft,developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance...To meet the emerging demands for thermal protection materials for hypersonic aircraft,developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge.Herein,we report novel porous(Ta_(0.2)Nb_(0.2)Ti_(0.2)Zr_(0.2)Hf_(0.2))C high-entropy carbide(PHEC)ceramics fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol(FA)as precursors.The PHEC ceramics are constructed of microspheres with a size of 2µm,leading to a high porosity of 91.3%and an interconnected frame.These microspheres consist of high-entropy carbide grains(20 nm),resulting in abundant interfaces and nanosized pores in the PHEC ceramics.Due to its unique hierarchical structure,the prepared PHEC ceramics have outstanding compressive strength(28.1±2 MPa)and exceptionally low thermal conductivity(κ_(T),0.046 W·m^(-1)·K^(-1))at room temperature.This makes it a promising thermal insulation materials for ultrahigh temperature applications.This work provides a cost-effective and facile strategy for producing porous ultrahigh-temperature ceramics.展开更多
A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from ...A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from being oxidized for 160 h at 1773 K with a weight loss of 6.9 mg/cm^2. The flexural strength retention ratio of the ZrB_2/SiO_2 coated composites is 87% after oxidation for 160 h at1773 K. The continuous SiO_2 glass layer embedded with the submicron ZrSiO_4 particles was formed during oxidation. This was helpful to lower the diffusion rate of oxygen and improve the stability of SiO_2 glass film, thus improving the oxidation resistance of the coated samples. After thermal cycles between 1773 K and room temperature for 15 times, penetrated cracks formed in the coating. The weight loss of the ZrB_2/SiO_2 coated sample presented linear relationship, and the final weight loss per unit area was 6.35 mg/cm^2. The generation of the penetrative cracks and the debonded coating interface resulted in the failure of the ZrB_2/SiO_2 coating.展开更多
The core-shell Li4Ti5O（12） @ polyaniline composites（LP） have been synthesized via an in situ synthesis with different mole ratios（25：1, 50：1 and 100：1, aniline：LTO）. As an anode material of lithium-ion batte...The core-shell Li4Ti5O（12） @ polyaniline composites（LP） have been synthesized via an in situ synthesis with different mole ratios（25：1, 50：1 and 100：1, aniline：LTO）. As an anode material of lithium-ion batteries,the LP-2 electrodes（50：1） exhibit a high initial reversible capacity of 205 mAh g^（-1）with an initial coulombic efficiency of 97.6% at 0.1 C. Even at a high current density of 10 C, the reversible capacity of the LP-2 electrodes still remains at 102 mAh g^（-1）. Moreover, the LP-2 electrodes retain an impressive high capacity of 161 mAh g^（-1）after 100 cycles at 1 C, with 0.11% capacity fading per cycle. The promising electrochemical performance may be attributed to the significantly decreasing charge-transfer impedance of the LP composite and reductive polarity difference between the cathode and the electrolyte.展开更多
基金This research was supported by the National Natural Science Foundation of China(Nos.52173299 and 52372087)the Natural Science Foundation of Shaanxi Province(No.2021JZ-51).
文摘To meet the emerging demands for thermal protection materials for hypersonic aircraft,developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge.Herein,we report novel porous(Ta_(0.2)Nb_(0.2)Ti_(0.2)Zr_(0.2)Hf_(0.2))C high-entropy carbide(PHEC)ceramics fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol(FA)as precursors.The PHEC ceramics are constructed of microspheres with a size of 2µm,leading to a high porosity of 91.3%and an interconnected frame.These microspheres consist of high-entropy carbide grains(20 nm),resulting in abundant interfaces and nanosized pores in the PHEC ceramics.Due to its unique hierarchical structure,the prepared PHEC ceramics have outstanding compressive strength(28.1±2 MPa)and exceptionally low thermal conductivity(κ_(T),0.046 W·m^(-1)·K^(-1))at room temperature.This makes it a promising thermal insulation materials for ultrahigh temperature applications.This work provides a cost-effective and facile strategy for producing porous ultrahigh-temperature ceramics.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51302160 and 51402177)the Science and Technique Talent Project of Shaanxi Province (Grant No. 2016KJXX-07)+2 种基金Natural Science Foundation of Shaanxi Province (Grant No. 2018JM5038)Natural Science Foundation of Education Department of Shaanxi Province (Grant No. 14JK1103)Research Foundation of Shaanxi University of Science & Technology (Grant No. BJ14-20)
文摘A dense ZrB_2 particles reinforced glass(ZrB_2/SiO_2) coating was prepared on the SiC coated carbon/carbon composites by a facile sol-dipping approach. The prepared ZrB2/SiO2 coating could protect the composites from being oxidized for 160 h at 1773 K with a weight loss of 6.9 mg/cm^2. The flexural strength retention ratio of the ZrB_2/SiO_2 coated composites is 87% after oxidation for 160 h at1773 K. The continuous SiO_2 glass layer embedded with the submicron ZrSiO_4 particles was formed during oxidation. This was helpful to lower the diffusion rate of oxygen and improve the stability of SiO_2 glass film, thus improving the oxidation resistance of the coated samples. After thermal cycles between 1773 K and room temperature for 15 times, penetrated cracks formed in the coating. The weight loss of the ZrB_2/SiO_2 coated sample presented linear relationship, and the final weight loss per unit area was 6.35 mg/cm^2. The generation of the penetrative cracks and the debonded coating interface resulted in the failure of the ZrB_2/SiO_2 coating.
基金supported by the “973” Special Preliminary Study Plan (No. 2014CB260411)the National Key Technology R&D Program (No. 2013BAF09B02)+2 种基金the National Natural Science Foundation of China (No. 51472152)the Innovation Team Assistance Foundation of Shaanxi Province (No. 2013KCT-06)the Graduate Innovation Fund of Shaanxi University of Science and Technology
文摘The core-shell Li4Ti5O（12） @ polyaniline composites（LP） have been synthesized via an in situ synthesis with different mole ratios（25：1, 50：1 and 100：1, aniline：LTO）. As an anode material of lithium-ion batteries,the LP-2 electrodes（50：1） exhibit a high initial reversible capacity of 205 mAh g^（-1）with an initial coulombic efficiency of 97.6% at 0.1 C. Even at a high current density of 10 C, the reversible capacity of the LP-2 electrodes still remains at 102 mAh g^（-1）. Moreover, the LP-2 electrodes retain an impressive high capacity of 161 mAh g^（-1）after 100 cycles at 1 C, with 0.11% capacity fading per cycle. The promising electrochemical performance may be attributed to the significantly decreasing charge-transfer impedance of the LP composite and reductive polarity difference between the cathode and the electrolyte.
