The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Litong Guo - One of the best experts on this subject based on the ideXlab platform.
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Dynamic oxidation protective ultrahigh temperature ceramic TaB2-20%wtSiC composite coating for carbon material
Composites Part B: Engineering, 2019Co-Authors: Xuanru Ren, Wenhao Wang, Tianqi Shang, Peizhong Feng, Litong GuoAbstract:Abstract TaB 2 –20%wtSiC composite coating containing high content of TaB 2 was synthesized by liquid phase sintering method to enhance the anti-oxidation property of the carbon materials. The coated sample exhibits a trend of sustained weight gain whose final value is about 1.35%, while there is no weight Loss Zone in weight Loss rate curves, but a rapid weight gain region around 800 °C. The generated compound glass layer presents a structure of Ta-oxides/Ta B Si O/SiO 2 triple glass layer. The rough surface of top Ta-oxides layer increases the oxidation defensive area of the glass layer, while the self-sealing Ta B Si O/SiO 2 compound glass ceramics layer can arrest the microcracks, blocking the fast diffusion channel of oxygen.
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Low temperature synthesis of pure phase TaB2 powders and its oxidation protection modification behaviors for Si-based ceramic coating in dynamic oxidation environments
Ceramics International, 2018Co-Authors: Xuanru Ren, Peizhong Feng, Litong Guo, Lifeng Wang, Ping Zhang, Xiaojun SunAbstract:Abstract To reveal the generation mechanisms of the Ta-Si-O glass ceramics layer in dynamic oxidation environments, a 40 wt% TaB 2 -SiC coating was prepared by liquid phase sintering method. To obtain pure phase TaB 2 powders at lower temperature (1500 °C), excessive B 2 O 3 powders were added in raw materials to eliminate the TaC byproduct phase. The hexagonal pure phase TaB 2 powders own average particle size of about 386 nm. During the TGA dynamic oxidation tests, after the modification of 40 wt% TaB 2 , the initial weight Loss temperature of the sample delayed by about 48%, while the weight Loss percentage and rate in fastest weight Loss Zone decreased by about 61% and 53%, respectively. During oxidation, the generated Ta-oxides were peeled and carried away by the formed fluid SiO 2 glass layer to form “Ta-oxides halation” at first, which results the dissolution of Ta-oxides in the SiO 2 glass, thus forming the Ta-Si-O glass ceramics with dendritic structure. With the spread of the SiO 2 glass layer and growth of the Ta-Si-O dendrite, the Ta-Si-O glass ceramics gradually cover on the surface of the SiO 2 glass layer, forming the structure of Ta-Si-O/SiO 2 double glass layer that is capable of sealing and arresting of microcracks.
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Ultrahigh temperature ceramic HfB2-SiC coating by liquid phase sintering method to protect carbon materials from oxidation
Materials Chemistry and Physics, 2018Co-Authors: Xuanru Ren, Wenhao Wang, Peizhong Feng, Litong GuoAbstract:Abstract To investigate the anti-oxidation modification behaviors and mechanisms of the pure HfB2 phase in dynamic aerobic environment, HfB2-SiC coating was prepared through liquid phase sintering method. The average particle size of the synthetic pure phase HfB2 powders is about 335 nm. The TG curve of pure HfB2 powders exhibits excellent anti-oxidation modification ability for Si-based coating. After the modification of HfB2 phase, the anti-oxidation ability of SiC coating achieved prominent improvement. The initiative mass Loss temperature of SiC coating lagged by 41.8%, while the percentage of mass Loss and rate in fastest mass-Loss Zone of the SiC coating lagged by 57.6% and 33.3%, respectively. The generated B2O3 is responsible for the obviously improved oxidation resistance below 1200 °C. It compensates the oxidation protection weaknesses of the Si-based ceramic coating in this temperature region. With the fluid of the SiO2 glass layer, the dispersed Hf-oxides were inlaid in it to form the compound Hf-O-Si glass layer. The Hf-oxides heterogeneous phases with ultra-high melting temperature are able to improve the stability of the SiO2 glass layer at ultra-high temperature. It improves the ability of microcracks restriction and reduces the erosion of oxygen to the carbon matrix.
J. D. Callen - One of the best experts on this subject based on the ideXlab platform.
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Effects of electron cyclotron resonance heating (ECRH)-induced direct Loss flux on neoclassical transport in a bumpy stellarator
Physics of Plasmas, 2007Co-Authors: Jae Chun Seol, C. C. Hegna, J. D. CallenAbstract:Energetic electron populations can substantially modify the neoclassical transport properties in stellarators. A model accounting for this change in transport is developed assuming the presence of electron cyclotron resonance heating (ECRH). The quasilinear diffusion coefficient for second-harmonic X-mode ECRH is developed for a stellarator. Care is taken in accounting for the pitch-angle dependence of the quasilinear diffusion coefficient since application to experiments with narrow resonance Zones is of interest. Weakly relativistic effects are considered through the mass effect on the cyclotron frequency. For trapped particles in a three-dimensional configuration, collisionless Loss Zones exist in velocity space. Radio-frequency (rf) waves accelerate trapped electrons into the direct Loss Zone in conventional stellarators and produce a direct Loss flux. An analytic expression for this Loss flux is derived; it is proportional to the rf field strength and the value of the zeroth-order distribution functi...
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ECRH and its Effects on Neoclassical Transport in a Stellarator
Bulletin of the American Physical Society, 2006Co-Authors: Jae Chun Seol, C. C. Hegna, J. D. CallenAbstract:Abstract Energetic electron populations can substantially modify the neoclassical transport properties in stellarators. A model accounting for this change in transport is developed assuming the presence of electron cyclotron resonance heating (ECRH). The quasilinear diffusion coefficient for second harmonic X-mode ECRH is developed for a bumpy stellarator. Care is taken in accounting for the pitch-angle dependence of the quasilinear diffusion coefficient since application to experiments with narrow resonance Zones is of interest. Weakly relativistic effects are considered through the mass effect on the cyclotron frequency. For trapped particles in a three dimensional configuration, collisionless Loss Zones exist in velocity space. Radio-frequency (rf) waves accelerate trapped electrons into the direct Loss Zone in bumpy stellarators and produce a direct Loss flux. An analytic expression for this Loss flux is derived; it is proportional to the rf field strength and the value of the zeroth order distribution function at the minimum speed for collisionless Loss. The direct Loss flux of electrons is another source of a non-ambipolar particle flux in bumpy stellarators. This additional non-ambipolar flux modifies the ambipolarity equation which generally has multiple roots for the radial electric field. An electron root (large positive Er) is easily obtained if the electrons are in the 1/ν regime and the ions are in the ν regime.
Xuanru Ren - One of the best experts on this subject based on the ideXlab platform.
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Dynamic oxidation protective ultrahigh temperature ceramic TaB2-20%wtSiC composite coating for carbon material
Composites Part B: Engineering, 2019Co-Authors: Xuanru Ren, Wenhao Wang, Tianqi Shang, Peizhong Feng, Litong GuoAbstract:Abstract TaB 2 –20%wtSiC composite coating containing high content of TaB 2 was synthesized by liquid phase sintering method to enhance the anti-oxidation property of the carbon materials. The coated sample exhibits a trend of sustained weight gain whose final value is about 1.35%, while there is no weight Loss Zone in weight Loss rate curves, but a rapid weight gain region around 800 °C. The generated compound glass layer presents a structure of Ta-oxides/Ta B Si O/SiO 2 triple glass layer. The rough surface of top Ta-oxides layer increases the oxidation defensive area of the glass layer, while the self-sealing Ta B Si O/SiO 2 compound glass ceramics layer can arrest the microcracks, blocking the fast diffusion channel of oxygen.
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Low temperature synthesis of pure phase TaB2 powders and its oxidation protection modification behaviors for Si-based ceramic coating in dynamic oxidation environments
Ceramics International, 2018Co-Authors: Xuanru Ren, Peizhong Feng, Litong Guo, Lifeng Wang, Ping Zhang, Xiaojun SunAbstract:Abstract To reveal the generation mechanisms of the Ta-Si-O glass ceramics layer in dynamic oxidation environments, a 40 wt% TaB 2 -SiC coating was prepared by liquid phase sintering method. To obtain pure phase TaB 2 powders at lower temperature (1500 °C), excessive B 2 O 3 powders were added in raw materials to eliminate the TaC byproduct phase. The hexagonal pure phase TaB 2 powders own average particle size of about 386 nm. During the TGA dynamic oxidation tests, after the modification of 40 wt% TaB 2 , the initial weight Loss temperature of the sample delayed by about 48%, while the weight Loss percentage and rate in fastest weight Loss Zone decreased by about 61% and 53%, respectively. During oxidation, the generated Ta-oxides were peeled and carried away by the formed fluid SiO 2 glass layer to form “Ta-oxides halation” at first, which results the dissolution of Ta-oxides in the SiO 2 glass, thus forming the Ta-Si-O glass ceramics with dendritic structure. With the spread of the SiO 2 glass layer and growth of the Ta-Si-O dendrite, the Ta-Si-O glass ceramics gradually cover on the surface of the SiO 2 glass layer, forming the structure of Ta-Si-O/SiO 2 double glass layer that is capable of sealing and arresting of microcracks.
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Ultrahigh temperature ceramic HfB2-SiC coating by liquid phase sintering method to protect carbon materials from oxidation
Materials Chemistry and Physics, 2018Co-Authors: Xuanru Ren, Wenhao Wang, Peizhong Feng, Litong GuoAbstract:Abstract To investigate the anti-oxidation modification behaviors and mechanisms of the pure HfB2 phase in dynamic aerobic environment, HfB2-SiC coating was prepared through liquid phase sintering method. The average particle size of the synthetic pure phase HfB2 powders is about 335 nm. The TG curve of pure HfB2 powders exhibits excellent anti-oxidation modification ability for Si-based coating. After the modification of HfB2 phase, the anti-oxidation ability of SiC coating achieved prominent improvement. The initiative mass Loss temperature of SiC coating lagged by 41.8%, while the percentage of mass Loss and rate in fastest mass-Loss Zone of the SiC coating lagged by 57.6% and 33.3%, respectively. The generated B2O3 is responsible for the obviously improved oxidation resistance below 1200 °C. It compensates the oxidation protection weaknesses of the Si-based ceramic coating in this temperature region. With the fluid of the SiO2 glass layer, the dispersed Hf-oxides were inlaid in it to form the compound Hf-O-Si glass layer. The Hf-oxides heterogeneous phases with ultra-high melting temperature are able to improve the stability of the SiO2 glass layer at ultra-high temperature. It improves the ability of microcracks restriction and reduces the erosion of oxygen to the carbon matrix.
Jae Chun Seol - One of the best experts on this subject based on the ideXlab platform.
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Effects of electron cyclotron resonance heating (ECRH)-induced direct Loss flux on neoclassical transport in a bumpy stellarator
Physics of Plasmas, 2007Co-Authors: Jae Chun Seol, C. C. Hegna, J. D. CallenAbstract:Energetic electron populations can substantially modify the neoclassical transport properties in stellarators. A model accounting for this change in transport is developed assuming the presence of electron cyclotron resonance heating (ECRH). The quasilinear diffusion coefficient for second-harmonic X-mode ECRH is developed for a stellarator. Care is taken in accounting for the pitch-angle dependence of the quasilinear diffusion coefficient since application to experiments with narrow resonance Zones is of interest. Weakly relativistic effects are considered through the mass effect on the cyclotron frequency. For trapped particles in a three-dimensional configuration, collisionless Loss Zones exist in velocity space. Radio-frequency (rf) waves accelerate trapped electrons into the direct Loss Zone in conventional stellarators and produce a direct Loss flux. An analytic expression for this Loss flux is derived; it is proportional to the rf field strength and the value of the zeroth-order distribution functi...
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ECRH and its Effects on Neoclassical Transport in a Stellarator
Bulletin of the American Physical Society, 2006Co-Authors: Jae Chun Seol, C. C. Hegna, J. D. CallenAbstract:Abstract Energetic electron populations can substantially modify the neoclassical transport properties in stellarators. A model accounting for this change in transport is developed assuming the presence of electron cyclotron resonance heating (ECRH). The quasilinear diffusion coefficient for second harmonic X-mode ECRH is developed for a bumpy stellarator. Care is taken in accounting for the pitch-angle dependence of the quasilinear diffusion coefficient since application to experiments with narrow resonance Zones is of interest. Weakly relativistic effects are considered through the mass effect on the cyclotron frequency. For trapped particles in a three dimensional configuration, collisionless Loss Zones exist in velocity space. Radio-frequency (rf) waves accelerate trapped electrons into the direct Loss Zone in bumpy stellarators and produce a direct Loss flux. An analytic expression for this Loss flux is derived; it is proportional to the rf field strength and the value of the zeroth order distribution function at the minimum speed for collisionless Loss. The direct Loss flux of electrons is another source of a non-ambipolar particle flux in bumpy stellarators. This additional non-ambipolar flux modifies the ambipolarity equation which generally has multiple roots for the radial electric field. An electron root (large positive Er) is easily obtained if the electrons are in the 1/ν regime and the ions are in the ν regime.
Peizhong Feng - One of the best experts on this subject based on the ideXlab platform.
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Dynamic oxidation protective ultrahigh temperature ceramic TaB2-20%wtSiC composite coating for carbon material
Composites Part B: Engineering, 2019Co-Authors: Xuanru Ren, Wenhao Wang, Tianqi Shang, Peizhong Feng, Litong GuoAbstract:Abstract TaB 2 –20%wtSiC composite coating containing high content of TaB 2 was synthesized by liquid phase sintering method to enhance the anti-oxidation property of the carbon materials. The coated sample exhibits a trend of sustained weight gain whose final value is about 1.35%, while there is no weight Loss Zone in weight Loss rate curves, but a rapid weight gain region around 800 °C. The generated compound glass layer presents a structure of Ta-oxides/Ta B Si O/SiO 2 triple glass layer. The rough surface of top Ta-oxides layer increases the oxidation defensive area of the glass layer, while the self-sealing Ta B Si O/SiO 2 compound glass ceramics layer can arrest the microcracks, blocking the fast diffusion channel of oxygen.
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Low temperature synthesis of pure phase TaB2 powders and its oxidation protection modification behaviors for Si-based ceramic coating in dynamic oxidation environments
Ceramics International, 2018Co-Authors: Xuanru Ren, Peizhong Feng, Litong Guo, Lifeng Wang, Ping Zhang, Xiaojun SunAbstract:Abstract To reveal the generation mechanisms of the Ta-Si-O glass ceramics layer in dynamic oxidation environments, a 40 wt% TaB 2 -SiC coating was prepared by liquid phase sintering method. To obtain pure phase TaB 2 powders at lower temperature (1500 °C), excessive B 2 O 3 powders were added in raw materials to eliminate the TaC byproduct phase. The hexagonal pure phase TaB 2 powders own average particle size of about 386 nm. During the TGA dynamic oxidation tests, after the modification of 40 wt% TaB 2 , the initial weight Loss temperature of the sample delayed by about 48%, while the weight Loss percentage and rate in fastest weight Loss Zone decreased by about 61% and 53%, respectively. During oxidation, the generated Ta-oxides were peeled and carried away by the formed fluid SiO 2 glass layer to form “Ta-oxides halation” at first, which results the dissolution of Ta-oxides in the SiO 2 glass, thus forming the Ta-Si-O glass ceramics with dendritic structure. With the spread of the SiO 2 glass layer and growth of the Ta-Si-O dendrite, the Ta-Si-O glass ceramics gradually cover on the surface of the SiO 2 glass layer, forming the structure of Ta-Si-O/SiO 2 double glass layer that is capable of sealing and arresting of microcracks.
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Ultrahigh temperature ceramic HfB2-SiC coating by liquid phase sintering method to protect carbon materials from oxidation
Materials Chemistry and Physics, 2018Co-Authors: Xuanru Ren, Wenhao Wang, Peizhong Feng, Litong GuoAbstract:Abstract To investigate the anti-oxidation modification behaviors and mechanisms of the pure HfB2 phase in dynamic aerobic environment, HfB2-SiC coating was prepared through liquid phase sintering method. The average particle size of the synthetic pure phase HfB2 powders is about 335 nm. The TG curve of pure HfB2 powders exhibits excellent anti-oxidation modification ability for Si-based coating. After the modification of HfB2 phase, the anti-oxidation ability of SiC coating achieved prominent improvement. The initiative mass Loss temperature of SiC coating lagged by 41.8%, while the percentage of mass Loss and rate in fastest mass-Loss Zone of the SiC coating lagged by 57.6% and 33.3%, respectively. The generated B2O3 is responsible for the obviously improved oxidation resistance below 1200 °C. It compensates the oxidation protection weaknesses of the Si-based ceramic coating in this temperature region. With the fluid of the SiO2 glass layer, the dispersed Hf-oxides were inlaid in it to form the compound Hf-O-Si glass layer. The Hf-oxides heterogeneous phases with ultra-high melting temperature are able to improve the stability of the SiO2 glass layer at ultra-high temperature. It improves the ability of microcracks restriction and reduces the erosion of oxygen to the carbon matrix.
