The coating layers of Tri-structural Isotropic Particles(TRISO)serve to protect the kernel and act as barriers to fission products.Sintering aids in the silicon carbide matrix variably react with TRISO coating layers,...The coating layers of Tri-structural Isotropic Particles(TRISO)serve to protect the kernel and act as barriers to fission products.Sintering aids in the silicon carbide matrix variably react with TRISO coating layers,leading to the destruction of the coating layers.Investigating how carbon content affects element diffusion in silicon carbide-based TRISO composite fuel is of great significance for predicting reactor safety.In this study,silicon carbide-based TRISO composite fuels with different carbon contents were prepared by adding varying amounts of phenolic resin to the silicon carbide matrix.X-ray Diffraction(XRD)and Scanning Electron Microscopy(SEM)were employed to characterize the phase composition,morphology,and microstructure of the composite fuels.The elemental content in each coating layer of TRISO was quantified using Energy-Dispersive X-ray Spectroscopy(EDS).The results demonstrated that the addition of phenolic resin promoted the uniform distribution of sintering aids in the silicon carbide matrix.The atomic percentage(at.%)of aluminum(Al)in the pyrolytic carbon layer of the TRISO particles reached its lowest value of 0.55%when the phenolic resin addition was 1%.This is because the addition of phenolic resin caused the Al and silicon(Si)in the matrix to preferentially react with the carbon in the phenolic resin to form a metastable liquid phase,rather than preferentially consuming the pyrolytic carbon in the outer coating layer of the TRISO particles.The findings suggest that carbon addition through phenolic resin incorporation can effectively mitigate the deleterious reactions between the TRISO coating layers and sintering aids,thereby enhancing the durability and safety of silicon carbide-based TRISO composite fuels.展开更多
This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three c...This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three chemical vapor deposition （CVD） reactors. A two-dimensional model for the gas flow, heat transfer, and mass transfer was coupled to the gas-phase reaction and surface reaction mechanism for the deposition of polycrystalline silicon from trichlorosilane （TCS）-hydrogen system. The model was verified by comparing the simulated growth rate with the experimental and numerical data in the open literature. Computed results in the reactors indicate that the deposition characteristics are closely related to the momentum, thermal and mass boundary layer thickness. To yield higher deposition rate, there should be higher concentration of TCS gas on the substrate, and there should also be thinner boundary layer of HCl gas so that HCl gas could be pushed away from the surface of the substrate immediately.展开更多
When hyperthermal atomic oxygen collides with a silicon surface, an ultrathin oxidation regime characterized by fractional atomic-oxygen anions having low diffusive and reactive barriers, along with their enhanced dif...When hyperthermal atomic oxygen collides with a silicon surface, an ultrathin oxidation regime characterized by fractional atomic-oxygen anions having low diffusive and reactive barriers, along with their enhanced diffusion due to both the electric field and image potential, will form on the surface. In ac- cordance with these properties, an attempt was made in the present study to modify the Almeida- Goncalves-Baumvol (AGB) model by setting the diffusivity and reaction rate constant to be diffu- sion-length dependence. According to the modified model, numerical parametric studies for oxidation thin growth were performed. The dependencies of the diffusion coefficient, the reaction rate constant, the attenuation length, and the adjustable parameter upon the translational kinetic energy, flux, tem- perature, and tangential flux of atomic oxygen were analyzed briefly via the fitting of the experimental data given by Tagawa et al. The numerical results confirmed the rationality of the modified diffu- sion-reaction model. The model together with the computer code developed in this study would be a useful tool for thickness evaluation of the protective film against the oxidation of atomic oxygen toward spacecraft surface materials in LEO environment.展开更多
This paper studies the effects of silane back diffusion in the initial plasma ignition stage on the properties of microcrystalline silicon （μc-Si：H） films by Raman spectroscopy and spectroscopic ellipsometry, thro...This paper studies the effects of silane back diffusion in the initial plasma ignition stage on the properties of microcrystalline silicon （μc-Si：H） films by Raman spectroscopy and spectroscopic ellipsometry, through delaying the injection of SiH4 gas to the reactor before plasma ignition. Compared with standard discharge condition, delayed SiH4 gas condition could prevent the back diffusion of Sill4 from the reactor to the deposition region effectively, which induced the formation of a thick amorphous incubation layer in the interface between bulk film and glass substrate. Applying this method, it obtains the improvement of spectral response in the middle and long wavelength region by combining this method with solar cell fabrication. Finally, results are explained by modifying zero-order analytical model, and a good agreement is found between the model and experiments concerning the optimum delayed injection time.展开更多
基金funded by the Shanghai Academic/Technology Research Leader(Project No.21XD1432000).
文摘The coating layers of Tri-structural Isotropic Particles(TRISO)serve to protect the kernel and act as barriers to fission products.Sintering aids in the silicon carbide matrix variably react with TRISO coating layers,leading to the destruction of the coating layers.Investigating how carbon content affects element diffusion in silicon carbide-based TRISO composite fuel is of great significance for predicting reactor safety.In this study,silicon carbide-based TRISO composite fuels with different carbon contents were prepared by adding varying amounts of phenolic resin to the silicon carbide matrix.X-ray Diffraction(XRD)and Scanning Electron Microscopy(SEM)were employed to characterize the phase composition,morphology,and microstructure of the composite fuels.The elemental content in each coating layer of TRISO was quantified using Energy-Dispersive X-ray Spectroscopy(EDS).The results demonstrated that the addition of phenolic resin promoted the uniform distribution of sintering aids in the silicon carbide matrix.The atomic percentage(at.%)of aluminum(Al)in the pyrolytic carbon layer of the TRISO particles reached its lowest value of 0.55%when the phenolic resin addition was 1%.This is because the addition of phenolic resin caused the Al and silicon(Si)in the matrix to preferentially react with the carbon in the phenolic resin to form a metastable liquid phase,rather than preferentially consuming the pyrolytic carbon in the outer coating layer of the TRISO particles.The findings suggest that carbon addition through phenolic resin incorporation can effectively mitigate the deleterious reactions between the TRISO coating layers and sintering aids,thereby enhancing the durability and safety of silicon carbide-based TRISO composite fuels.
基金Supported by the Natural Science Foundation of Shandong Province of China （ZR2009BM011） the Doctor Foundation of Shandong Province of China （BS2010NJ005）
文摘This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three chemical vapor deposition （CVD） reactors. A two-dimensional model for the gas flow, heat transfer, and mass transfer was coupled to the gas-phase reaction and surface reaction mechanism for the deposition of polycrystalline silicon from trichlorosilane （TCS）-hydrogen system. The model was verified by comparing the simulated growth rate with the experimental and numerical data in the open literature. Computed results in the reactors indicate that the deposition characteristics are closely related to the momentum, thermal and mass boundary layer thickness. To yield higher deposition rate, there should be higher concentration of TCS gas on the substrate, and there should also be thinner boundary layer of HCl gas so that HCl gas could be pushed away from the surface of the substrate immediately.
基金Supported by the National Natural Science Foundation of China (Grant No. 10572016)
文摘When hyperthermal atomic oxygen collides with a silicon surface, an ultrathin oxidation regime characterized by fractional atomic-oxygen anions having low diffusive and reactive barriers, along with their enhanced diffusion due to both the electric field and image potential, will form on the surface. In ac- cordance with these properties, an attempt was made in the present study to modify the Almeida- Goncalves-Baumvol (AGB) model by setting the diffusivity and reaction rate constant to be diffu- sion-length dependence. According to the modified model, numerical parametric studies for oxidation thin growth were performed. The dependencies of the diffusion coefficient, the reaction rate constant, the attenuation length, and the adjustable parameter upon the translational kinetic energy, flux, tem- perature, and tangential flux of atomic oxygen were analyzed briefly via the fitting of the experimental data given by Tagawa et al. The numerical results confirmed the rationality of the modified diffu- sion-reaction model. The model together with the computer code developed in this study would be a useful tool for thickness evaluation of the protective film against the oxidation of atomic oxygen toward spacecraft surface materials in LEO environment.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No. 2006CB202601)
文摘This paper studies the effects of silane back diffusion in the initial plasma ignition stage on the properties of microcrystalline silicon （μc-Si：H） films by Raman spectroscopy and spectroscopic ellipsometry, through delaying the injection of SiH4 gas to the reactor before plasma ignition. Compared with standard discharge condition, delayed SiH4 gas condition could prevent the back diffusion of Sill4 from the reactor to the deposition region effectively, which induced the formation of a thick amorphous incubation layer in the interface between bulk film and glass substrate. Applying this method, it obtains the improvement of spectral response in the middle and long wavelength region by combining this method with solar cell fabrication. Finally, results are explained by modifying zero-order analytical model, and a good agreement is found between the model and experiments concerning the optimum delayed injection time.
