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 available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112...The available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112 and Titan) and the long-grain (Diamond and Wells) rough rice varieties were dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric analyzer. Drying kinetics models were studied for four well-known models: Page, Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants were determined for the four studied models. The initial moisture content of rough rice was 28.2% db. Profound moisture reduction was observed during the first three hours of drying, followed by less moisture content reduction. The results showed that at the drying temperature of 100°C and after 6 hours of the drying process, the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of drying under the studied temperature range of 40°C to 100°C. The drying rate was higher with the higher temperature levels during the first three hours. Among all the studied models, the Page, Newton, and Logarithmic models best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge that arose from these results led to evolving a mathematical solution by joining the three models in one equation. The combined model showed the best fit for all the studied cases, with R<sup>2</sup> ranging between 0.9999 and 0.9954 for the medium- and long-grain rice varieties. Increasing the drying temperature increased the effective moisture diffusivity values. The highest effective moisture diffusivity of 18.104 × 10<sup>-9</sup> m<sup>2</sup>/s was obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between 17.77 and 24.48 kJ/mol for the four rough rice varieties.展开更多
The grain growth and thermal stability of nanocrystalline Ni-TiO2composites were systematically investigated.Thenanocrystalline Ni-TiO2composites with different contents of TiO2were prepared via electroplating method ...The grain growth and thermal stability of nanocrystalline Ni-TiO2composites were systematically investigated.Thenanocrystalline Ni-TiO2composites with different contents of TiO2were prepared via electroplating method with the variation ofTiO2nano-particles concentration.The effect of TiO2content on the grain size,phase structure and microhardness was investigatedin detail.The corresponding grain growth and diffusion mechanisms during the heating process were also discussed.The optimalmicrohardness of HV50270was achieved for the composite with addition of20g/L TiO2nano-particles after annealing at400°C for90min.The calculation of the activation energy indicated that lattice diffusion dominated at high temperatures for thenanocrystalline Ni-TiO2composites.It was indicated that the increase of TiO2nano-particles content took effect on restricting thegrain growth at high temperatures by increasing the grain growth activation energy.展开更多
Effectiveness of microwave sintering process through investigation of microstructural characteristics and electrical properties of x(0.94PbZn_ 1/3Nb_ 2/3O_3 + 0.06BaTiO_3)+(1-x)PbZr_yTi_ 1-yO_3(PBZNZT)ceramics with x=...Effectiveness of microwave sintering process through investigation of microstructural characteristics and electrical properties of x(0.94PbZn_ 1/3Nb_ 2/3O_3 + 0.06BaTiO_3)+(1-x)PbZr_yTi_ 1-yO_3(PBZNZT)ceramics with x=0.6 and y=0.52 was evaluated.The relative density of 95% was achieved with sintering at 800℃ for 2 h.The small grain growth exponents indicate how easy the grain growth in these materials sintered using microwave radiation.Grain growth rate increases abruptly and is higher than that of conventional sintering at a temperature higher than 1050℃.This is attributed to the lower activation energy and higher grain boundary mobility.The activation energy required for the grain growth is found to be 132kJ/mol.Higher remanent polarization(Pr=50.1μC/cm2)and increase in remanent polarization with sintering temperature are observed in microwave sintering process when compared to that of conventional sintering process,due to fast increase in grain growth rate and homogeneity in the specimen.The results indicate lower sintering energy and reduction of PbO pollution in the working environment by microwave sintering process.展开更多
利用热重分析仪,对比了不同反应温度、不同水蒸气浓度对煅烧石灰石碳酸化反应的影响。碳酸化反应温度在500℃时,反应初期水蒸气对碳酸化反应的影响并不明显,反应10 min之后,在含有1.5%、10%和20%(体积分数)水蒸气条件下碳酸化转化率比...利用热重分析仪,对比了不同反应温度、不同水蒸气浓度对煅烧石灰石碳酸化反应的影响。碳酸化反应温度在500℃时,反应初期水蒸气对碳酸化反应的影响并不明显,反应10 min之后,在含有1.5%、10%和20%(体积分数)水蒸气条件下碳酸化转化率比无水蒸气条件下转化率分别提高了19.8%、27.2%和30.5%。水蒸气的存在有助于提高碳酸化反应转化率,但随着水蒸气浓度的增加转化率增加幅度减小。利用随机孔隙模型,对产物层扩散阶段扩散系数及反应活化能进行了计算。高温条件下,气氛中含有1.5%的水蒸气使反应活化能从237.7 k J·mol-1降低到179.9 k J·mol-1,提高水蒸气浓度到10%和20%后,反应活化能从156.6 k J·mol-1降低到148.6 k J·mol-1。不同水蒸气浓度条件下,碳酸化反应存在两个明显特征:一是大约在550℃处存在一个明显扩散系数的斜率变化,这一温度与气氛中是否存在水蒸气无关;另一特征是随着反应温度的提高,水蒸气的促进作用减弱。依据实验和模型计算结果,推测了当反应处于产物层扩散阶段时水蒸气对碳酸化反应影响的作用机理。展开更多
为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,...为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,反应活化能为57.3 k J/mol.原位红外漫反射光谱（DRIFTS）实验结果表明：NH3能够强吸附到催化剂表面并达到饱和,进一步增加NH3的浓度并不能增加NO的转化速率;NO在有氧条件下能吸附到催化剂表面生成吸附态NO2和亚硝酸盐;在低于270℃的情况下SCR反应遵循Langmuir-Hinshelw ood（L-H）反应机理,在高于270℃的情况下则主要遵循Eley-Rideal（E-R）反应机理.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 available literature revealed a gap in reporting the rough rice drying kinetics parameters under isothermal conditions, particularly for Arkansas medium- and long-grain varieties. Therefore, medium-grain (RO170112 and Titan) and the long-grain (Diamond and Wells) rough rice varieties were dried under isothermal conditions. The drying process occurred under 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C in a system emulating the thermogravimetric analyzer. Drying kinetics models were studied for four well-known models: Page, Newton, Logarithmic, and Henderson & Pabis. The drying kinetics constants were determined for the four studied models. The initial moisture content of rough rice was 28.2% db. Profound moisture reduction was observed during the first three hours of drying, followed by less moisture content reduction. The results showed that at the drying temperature of 100°C and after 6 hours of the drying process, the lowest moisture content reached 13.9% (db) for Titan rough rice. The drying rate of rough rice ranged between 7.41 and 2.01%/h during the first hour of drying under the studied temperature range of 40°C to 100°C. The drying rate was higher with the higher temperature levels during the first three hours. Among all the studied models, the Page, Newton, and Logarithmic models best fit 25%, 25%, and 50% of the twenty-eight studied cases. The challenge that arose from these results led to evolving a mathematical solution by joining the three models in one equation. The combined model showed the best fit for all the studied cases, with R<sup>2</sup> ranging between 0.9999 and 0.9954 for the medium- and long-grain rice varieties. Increasing the drying temperature increased the effective moisture diffusivity values. The highest effective moisture diffusivity of 18.104 × 10<sup>-9</sup> m<sup>2</sup>/s was obtained at the drying temperature of 100°C for medium-grain rice, Titan. The activation energy values ranged between 17.77 and 24.48 kJ/mol for the four rough rice varieties.
基金Project(51401024)supported by the National Natural Science Foundation of ChinaProject(20150942006)supported by Basic Research Program of Beijing Institute of Technology,China
文摘The grain growth and thermal stability of nanocrystalline Ni-TiO2composites were systematically investigated.Thenanocrystalline Ni-TiO2composites with different contents of TiO2were prepared via electroplating method with the variation ofTiO2nano-particles concentration.The effect of TiO2content on the grain size,phase structure and microhardness was investigatedin detail.The corresponding grain growth and diffusion mechanisms during the heating process were also discussed.The optimalmicrohardness of HV50270was achieved for the composite with addition of20g/L TiO2nano-particles after annealing at400°C for90min.The calculation of the activation energy indicated that lattice diffusion dominated at high temperatures for thenanocrystalline Ni-TiO2composites.It was indicated that the increase of TiO2nano-particles content took effect on restricting thegrain growth at high temperatures by increasing the grain growth activation energy.
文摘Effectiveness of microwave sintering process through investigation of microstructural characteristics and electrical properties of x(0.94PbZn_ 1/3Nb_ 2/3O_3 + 0.06BaTiO_3)+(1-x)PbZr_yTi_ 1-yO_3(PBZNZT)ceramics with x=0.6 and y=0.52 was evaluated.The relative density of 95% was achieved with sintering at 800℃ for 2 h.The small grain growth exponents indicate how easy the grain growth in these materials sintered using microwave radiation.Grain growth rate increases abruptly and is higher than that of conventional sintering at a temperature higher than 1050℃.This is attributed to the lower activation energy and higher grain boundary mobility.The activation energy required for the grain growth is found to be 132kJ/mol.Higher remanent polarization(Pr=50.1μC/cm2)and increase in remanent polarization with sintering temperature are observed in microwave sintering process when compared to that of conventional sintering process,due to fast increase in grain growth rate and homogeneity in the specimen.The results indicate lower sintering energy and reduction of PbO pollution in the working environment by microwave sintering process.
文摘利用热重分析仪,对比了不同反应温度、不同水蒸气浓度对煅烧石灰石碳酸化反应的影响。碳酸化反应温度在500℃时,反应初期水蒸气对碳酸化反应的影响并不明显,反应10 min之后,在含有1.5%、10%和20%(体积分数)水蒸气条件下碳酸化转化率比无水蒸气条件下转化率分别提高了19.8%、27.2%和30.5%。水蒸气的存在有助于提高碳酸化反应转化率,但随着水蒸气浓度的增加转化率增加幅度减小。利用随机孔隙模型,对产物层扩散阶段扩散系数及反应活化能进行了计算。高温条件下,气氛中含有1.5%的水蒸气使反应活化能从237.7 k J·mol-1降低到179.9 k J·mol-1,提高水蒸气浓度到10%和20%后,反应活化能从156.6 k J·mol-1降低到148.6 k J·mol-1。不同水蒸气浓度条件下,碳酸化反应存在两个明显特征:一是大约在550℃处存在一个明显扩散系数的斜率变化,这一温度与气氛中是否存在水蒸气无关;另一特征是随着反应温度的提高,水蒸气的促进作用减弱。依据实验和模型计算结果,推测了当反应处于产物层扩散阶段时水蒸气对碳酸化反应影响的作用机理。
文摘为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,反应活化能为57.3 k J/mol.原位红外漫反射光谱（DRIFTS）实验结果表明：NH3能够强吸附到催化剂表面并达到饱和,进一步增加NH3的浓度并不能增加NO的转化速率;NO在有氧条件下能吸附到催化剂表面生成吸附态NO2和亚硝酸盐;在低于270℃的情况下SCR反应遵循Langmuir-Hinshelw ood（L-H）反应机理,在高于270℃的情况下则主要遵循Eley-Rideal（E-R）反应机理.
