Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating thi...Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating this chemical interaction.In this study,first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface.The interaction between these two fission products and the Cr coating were studied systematically,and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model,respectively.The results showed that the Cs and I migration barriers were significantly lower than that of Cr,and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors(below 1000 K),demonstrating the strong penetration ability of Cs and I.Furthermore,Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers,indicating that the grain boundary serves as a fast diffusion channel for Cs and I.展开更多
The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under s...The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650 ℃. The protection effect of an Al coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope, X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1) The oxidation rates are almost superposed in both air (no SO3) and in simulated coal-fired gas (containing SO3) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K2SO3 + 25%Na2SO3) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the Al over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, Al3Ni2, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.展开更多
Neutral salt spray corrosion experiments of spring steels with different Cr contents were carried out for different corrosion periods. The optical microscope was used to observe the macroscopic corrosion morphology of...Neutral salt spray corrosion experiments of spring steels with different Cr contents were carried out for different corrosion periods. The optical microscope was used to observe the macroscopic corrosion morphology of the steel surface. The corrosion pit morphology of steel surface was observed by laser scanning confocal microscopy and scanning electron microscopy, and three-dimensional simulation was carried out. At the same time, the corrosion products (rust layer) were qualitatively and quantitatively analysed by X-ray diffraction. As the results show, Cr is beneficial to improving corrosion resistance of the experimental steel matrix, and the higher the content of Cr, the stronger the corrosion resistance will be. With increase in Cr content in steel, the development of corrosion process will be more effectively suppressed. With the increase in Cr content, the denser the corrosion products, the stronger the bond with the metal matrix is. The corrosion products have obvious stratification;the outer layer is mainly composed of c-FeOOH, which is relatively loose and not firmly integrated with the matrix, while the inner layer contains a-FeOOH and Fe3O4, which are relatively dense and closely integrated with the matrix. The types of corrosion are constantly changing during different phases of corrosion.展开更多
基金the National Natural Science Foundation of China(No.12375282)the Key Laboratory of Computational Physical Sciences Project(Fudan University),Ministry of Education.
文摘Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating this chemical interaction.In this study,first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface.The interaction between these two fission products and the Cr coating were studied systematically,and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model,respectively.The results showed that the Cs and I migration barriers were significantly lower than that of Cr,and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors(below 1000 K),demonstrating the strong penetration ability of Cs and I.Furthermore,Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers,indicating that the grain boundary serves as a fast diffusion channel for Cs and I.
文摘The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650 ℃. The protection effect of an Al coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope, X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1) The oxidation rates are almost superposed in both air (no SO3) and in simulated coal-fired gas (containing SO3) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K2SO3 + 25%Na2SO3) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the Al over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, Al3Ni2, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.
文摘Neutral salt spray corrosion experiments of spring steels with different Cr contents were carried out for different corrosion periods. The optical microscope was used to observe the macroscopic corrosion morphology of the steel surface. The corrosion pit morphology of steel surface was observed by laser scanning confocal microscopy and scanning electron microscopy, and three-dimensional simulation was carried out. At the same time, the corrosion products (rust layer) were qualitatively and quantitatively analysed by X-ray diffraction. As the results show, Cr is beneficial to improving corrosion resistance of the experimental steel matrix, and the higher the content of Cr, the stronger the corrosion resistance will be. With increase in Cr content in steel, the development of corrosion process will be more effectively suppressed. With the increase in Cr content, the denser the corrosion products, the stronger the bond with the metal matrix is. The corrosion products have obvious stratification;the outer layer is mainly composed of c-FeOOH, which is relatively loose and not firmly integrated with the matrix, while the inner layer contains a-FeOOH and Fe3O4, which are relatively dense and closely integrated with the matrix. The types of corrosion are constantly changing during different phases of corrosion.
