The β-SiC/SiO2 core-shell nanowires with the 'stem-and-node' structure were synthesized in the presence of cerium oxide by the carbothermal reduction of the starch-SiO2 hybrids gel.The samples were characteri...The β-SiC/SiO2 core-shell nanowires with the 'stem-and-node' structure were synthesized in the presence of cerium oxide by the carbothermal reduction of the starch-SiO2 hybrids gel.The samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM) and energy-dispersed X-ray(EDX).The results showed that the nanowires consisted of a 20-35 nm diameter crystalline β-SiC core wrapped with a 2-5 n...展开更多
The rapid evolution of hypersonic vehicle technologies necessitates robust thermal protection systems capable of withstanding extreme oxidative ablation.This study introduces a novel gradient-architected ZrB2-MoSi_...The rapid evolution of hypersonic vehicle technologies necessitates robust thermal protection systems capable of withstanding extreme oxidative ablation.This study introduces a novel gradient-architected ZrB2-MoSi2-SiC dense layer embedded within a lightweight three-dimensional(3D)needled carbon fiber composite.Utilizing the volatility of ethanol and polycarbosilane,the ceramic slurry is selectively infused into targeted regions of the fibrous structure,optimizing the ZrB2to MoSi2ratio to enhance performance.The resulting dense layer exhibits exceptional emissivity,surpassing 0.90 in the 1-3μm range and exceeding 0.87 in the 2-14μm range.Moreover,it demonstrates remarkable oxidative ablation resistance.Specifically,at an optimized ZrB2to MoSi2ratio of 6:4,the dense layer achieves a minimal linear ablation rate of 0.015μm·s-1 under a 1.5 MW·m-2oxyacetylene flame for 1000 s.Even after exposure to oxyacetylene ablation at surface temperatures of approximately 1750℃for 1000 s,the dense layer retains its structural integrity,highlighting its enduring oxidation resistance.The incorporation of MoSi2not only enhances emissivity but also fortifies the ZrO2and SiO2oxide layers,crucial for environments with elevated oxygen levels,thereby mitigating the active oxidation of SiC.This combination of high emissivity and long-term oxidation resistance at ultra-high temperatures positions the ZrB2-MoSi2-SiC dense layer as an exceptionally promising candidate for advanced thermal protection in hypersonic vehicles.展开更多
Ablation under oxyacetylene torch with heat flux of 4186.8(10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration(CVI) combined with liqu...Ablation under oxyacetylene torch with heat flux of 4186.8(10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration(CVI) combined with liquid silicon infiltration(LSI) process.The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC.The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process.Bulk quantities of SiO2 nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation.The growth mechanism of the SiO_2 nanowires was interpreted with a developed vapor-liquid-solid(VLS) driven by the temperature gradient.展开更多
To improve the oxidation resistance of HfB2-SiC coatings on carbon/carbon composites at 1700°C in air,CeO2 was introduced to improve oxygen blocking and its mechanism was investigated.During the rapid oxida...To improve the oxidation resistance of HfB2-SiC coatings on carbon/carbon composites at 1700°C in air,CeO2 was introduced to improve oxygen blocking and its mechanism was investigated.During the rapid oxidation stage,CeO2 accelerated the formation of a multiphase glass layer on the coating surface.The maximum oxidation rates of CeO2-HfB2-SiC coatings with 1%,3%,and 5%CeO2 were 24.1%,20.3%,and 53.2%higher than that of the unmodified HfB2-SiC coating,respectively.In the stable oxidation stage,the maximum oxidation rates of coatings with 1%and 3%CeO2 decreased by 31.4%and 21.9%,respectively,demonstrating adequate inert protection.CeO2 is a“coagulant”and“stabilizer”in the composite glass layer.However,increasing the CeO2 content accelerates the reaction between the SiO2 glass phase and SiC,leading to a higher SiO2 consumption and reduced self-healing ability of the glass layer.The 1%CeO2-60%HfB2-39%SiC coating showed improved glass layer viscosity and stability,moderate SiO2 consumption,and better self-healing ability,significantly boosting the oxidation protection of the coating.展开更多
基金supported by the National Key Technology R&D Program (2007BEA08B01)the Natural Science Foundation of Fujian Province of China (E0710004)Joint Research Program of Fuzhou University (DH-548)
摘要The β-SiC/SiO2 core-shell nanowires with the 'stem-and-node' structure were synthesized in the presence of cerium oxide by the carbothermal reduction of the starch-SiO2 hybrids gel.The samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM) and energy-dispersed X-ray(EDX).The results showed that the nanowires consisted of a 20-35 nm diameter crystalline β-SiC core wrapped with a 2-5 n...
基金supported by the National Natural Science Foundation of China(Nos.52272060,51902067,51872066 and 52172041)the Key Program of National Natural Science Foundation of China(No.52032003)+5 种基金the Young Elite Scientists Sponsorship Program by CAST(No.2020QNRC001)China Postdoctoral Science Foundation(Nos.2019M651282 and 2022T150157)Heilongjiang Provincial Postdoctoral Science Foundation(Nos.LBH-Z19022 and LBH-TZ2207)Heilongjiang Touyan Innovation Team Program,Shanghai Aerospace Science and Technology Innovation Fund(No.SAST2019-012)the Fundamental Research Funds for the Central Universities(No.FRFCU5710051022)the Science Foundation of National Key Laboratory of Science and Technology on Advanced Composites in Special Environments(No.JCKYS2022603C011).
摘要The rapid evolution of hypersonic vehicle technologies necessitates robust thermal protection systems capable of withstanding extreme oxidative ablation.This study introduces a novel gradient-architected ZrB2-MoSi2-SiC dense layer embedded within a lightweight three-dimensional(3D)needled carbon fiber composite.Utilizing the volatility of ethanol and polycarbosilane,the ceramic slurry is selectively infused into targeted regions of the fibrous structure,optimizing the ZrB2to MoSi2ratio to enhance performance.The resulting dense layer exhibits exceptional emissivity,surpassing 0.90 in the 1-3μm range and exceeding 0.87 in the 2-14μm range.Moreover,it demonstrates remarkable oxidative ablation resistance.Specifically,at an optimized ZrB2to MoSi2ratio of 6:4,the dense layer achieves a minimal linear ablation rate of 0.015μm·s-1 under a 1.5 MW·m-2oxyacetylene flame for 1000 s.Even after exposure to oxyacetylene ablation at surface temperatures of approximately 1750℃for 1000 s,the dense layer retains its structural integrity,highlighting its enduring oxidation resistance.The incorporation of MoSi2not only enhances emissivity but also fortifies the ZrO2and SiO2oxide layers,crucial for environments with elevated oxygen levels,thereby mitigating the active oxidation of SiC.This combination of high emissivity and long-term oxidation resistance at ultra-high temperatures positions the ZrB2-MoSi2-SiC dense layer as an exceptionally promising candidate for advanced thermal protection in hypersonic vehicles.
基金supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110006110025)the National Natural Science Foundation of China(Grant No.U1134102)
摘要Ablation under oxyacetylene torch with heat flux of 4186.8(10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration(CVI) combined with liquid silicon infiltration(LSI) process.The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC.The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process.Bulk quantities of SiO2 nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation.The growth mechanism of the SiO_2 nanowires was interpreted with a developed vapor-liquid-solid(VLS) driven by the temperature gradient.
摘要To improve the oxidation resistance of HfB2-SiC coatings on carbon/carbon composites at 1700°C in air,CeO2 was introduced to improve oxygen blocking and its mechanism was investigated.During the rapid oxidation stage,CeO2 accelerated the formation of a multiphase glass layer on the coating surface.The maximum oxidation rates of CeO2-HfB2-SiC coatings with 1%,3%,and 5%CeO2 were 24.1%,20.3%,and 53.2%higher than that of the unmodified HfB2-SiC coating,respectively.In the stable oxidation stage,the maximum oxidation rates of coatings with 1%and 3%CeO2 decreased by 31.4%and 21.9%,respectively,demonstrating adequate inert protection.CeO2 is a“coagulant”and“stabilizer”in the composite glass layer.However,increasing the CeO2 content accelerates the reaction between the SiO2 glass phase and SiC,leading to a higher SiO2 consumption and reduced self-healing ability of the glass layer.The 1%CeO2-60%HfB2-39%SiC coating showed improved glass layer viscosity and stability,moderate SiO2 consumption,and better self-healing ability,significantly boosting the oxidation protection of the coating.