Mullite coating on recrystallized silicon carbide was successfully prepared by the sol-gel route. The cycling oxidation of coated recrystallized silicon carbide was performed at 1500℃. For comparison, the oxidation o...Mullite coating on recrystallized silicon carbide was successfully prepared by the sol-gel route. The cycling oxidation of coated recrystallized silicon carbide was performed at 1500℃. For comparison, the oxidation of uncoated recrystallized silicon carbide was also carried out at the same condition. The results in- dicated that a layer of compact, adhesive and crack free mullite coating was found on the recrystallized silicon carbide. After oxidation, the new coatings exhibit adherence and crack resistance under thermal cycling between room temperature and 1500℃, therefore the oxidation resistance capability of silicon carbide was enhanced. With the increase of the dipping frequencies, namely, the increase of the thickness of mullite coating, the oxidation resistance of silicon carbide would be futher improved. The formation mechanism of mullite coating was analyzed and discussed and the oxidation dynamics model of coatedmullite silicon carbide has been also proposed.展开更多
In order to improve the thermal stability of condensed polynuclear aromatic(COPNA) resin synthesized from vacuum residue, 1,4-benzenedimethanol was added to cure COPNA resin. The curing mechanism was investigated by p...In order to improve the thermal stability of condensed polynuclear aromatic(COPNA) resin synthesized from vacuum residue, 1,4-benzenedimethanol was added to cure COPNA resin. The curing mechanism was investigated by proton nuclear magnetic resonance spectrometry, solid carbon-13 nuclear magnetic resonance spectrometry and Fourier transform infrared spectroscopy. Microstructures of the uncured and the cured COPNA resins were studied by scanning electron microscopy and X-ray diffractometry. The thermal stability of COPNA resins before and after curing was tested by thermogravimetric analysis. The element composition of the cured COPNA resin heated at different temperatures was analyzed by an element analyzer. The results showed that the uncured COPNA resin reacted with the cross-linking agent during the curing process, and the curing mechanism was confirmed to be the electrophilic substitution reaction. Compared with the uncured COPNA resin, the cured COPNA resin had a smooth surface, well-ordered and streamlined sheet structure with more crystalline solids, better molecular arrangement and orientation. The weight loss process of the uncured and cured COPNA resins was divided into three stages. Carbon residue of the cured COPNA resin was 41.65% at 600 ℃, which was much higher than 25.02% of the uncured COPNA resin, which indicated that the cured COPNA resin had higher thermal stability.展开更多
21世纪以来,国际上针对高超声速技术的研究如雨后春笋般涌现,多种型号的高超声速飞行器不断被披露,使其逐渐成为彰显国防实力的大国重器。项目组在国家自然科学基金、国家重点研发计划、湖南省杰出青年基金等项目的持续支持下,紧扣我国...21世纪以来,国际上针对高超声速技术的研究如雨后春笋般涌现,多种型号的高超声速飞行器不断被披露,使其逐渐成为彰显国防实力的大国重器。项目组在国家自然科学基金、国家重点研发计划、湖南省杰出青年基金等项目的持续支持下,紧扣我国对吸气式高速飞行器总体设计的重大发展需求,围绕高超声速飞行器内外流耦合设计与多学科设计优化开展了深入研究,在气动外形设计、构型防热减阻、超燃冲压发动机流道设计、组合推进系统建模、内外流一体化和多学科设计优化等方面提出了一系列新理论、新方法和新技术,在Progress in Aerospace Sciences、Fuel、Energy、Energy Conversion and Management、Physics of Fluids、International Journal of Heat and Mass Transfer、Chinese Journal of Aeronautics等期刊发表学术论文150多篇,他引4000多次,其中8篇进入ESI前1%,出版学术专/译著7部,获省部级自然科学奖3项,形成了吸气式高速飞行器总体设计优化理论与方法体系,为国内吸气式高速飞行器的设计和工程研制提供了有力支撑。展开更多
文摘Mullite coating on recrystallized silicon carbide was successfully prepared by the sol-gel route. The cycling oxidation of coated recrystallized silicon carbide was performed at 1500℃. For comparison, the oxidation of uncoated recrystallized silicon carbide was also carried out at the same condition. The results in- dicated that a layer of compact, adhesive and crack free mullite coating was found on the recrystallized silicon carbide. After oxidation, the new coatings exhibit adherence and crack resistance under thermal cycling between room temperature and 1500℃, therefore the oxidation resistance capability of silicon carbide was enhanced. With the increase of the dipping frequencies, namely, the increase of the thickness of mullite coating, the oxidation resistance of silicon carbide would be futher improved. The formation mechanism of mullite coating was analyzed and discussed and the oxidation dynamics model of coatedmullite silicon carbide has been also proposed.
基金supported by the National Natural Science Foundation of China(51172285 and 51372277)the Fundamental Research Funds for the Central Universities(14CX02060A,15CX02084A)the Natural Science Foundation of Shandong Province(ZR2011EL030)
文摘In order to improve the thermal stability of condensed polynuclear aromatic(COPNA) resin synthesized from vacuum residue, 1,4-benzenedimethanol was added to cure COPNA resin. The curing mechanism was investigated by proton nuclear magnetic resonance spectrometry, solid carbon-13 nuclear magnetic resonance spectrometry and Fourier transform infrared spectroscopy. Microstructures of the uncured and the cured COPNA resins were studied by scanning electron microscopy and X-ray diffractometry. The thermal stability of COPNA resins before and after curing was tested by thermogravimetric analysis. The element composition of the cured COPNA resin heated at different temperatures was analyzed by an element analyzer. The results showed that the uncured COPNA resin reacted with the cross-linking agent during the curing process, and the curing mechanism was confirmed to be the electrophilic substitution reaction. Compared with the uncured COPNA resin, the cured COPNA resin had a smooth surface, well-ordered and streamlined sheet structure with more crystalline solids, better molecular arrangement and orientation. The weight loss process of the uncured and cured COPNA resins was divided into three stages. Carbon residue of the cured COPNA resin was 41.65% at 600 ℃, which was much higher than 25.02% of the uncured COPNA resin, which indicated that the cured COPNA resin had higher thermal stability.
文摘21世纪以来,国际上针对高超声速技术的研究如雨后春笋般涌现,多种型号的高超声速飞行器不断被披露,使其逐渐成为彰显国防实力的大国重器。项目组在国家自然科学基金、国家重点研发计划、湖南省杰出青年基金等项目的持续支持下,紧扣我国对吸气式高速飞行器总体设计的重大发展需求,围绕高超声速飞行器内外流耦合设计与多学科设计优化开展了深入研究,在气动外形设计、构型防热减阻、超燃冲压发动机流道设计、组合推进系统建模、内外流一体化和多学科设计优化等方面提出了一系列新理论、新方法和新技术,在Progress in Aerospace Sciences、Fuel、Energy、Energy Conversion and Management、Physics of Fluids、International Journal of Heat and Mass Transfer、Chinese Journal of Aeronautics等期刊发表学术论文150多篇,他引4000多次,其中8篇进入ESI前1%,出版学术专/译著7部,获省部级自然科学奖3项,形成了吸气式高速飞行器总体设计优化理论与方法体系,为国内吸气式高速飞行器的设计和工程研制提供了有力支撑。
