The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress r...The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress resistance of the composites were therefore computed based on experimental results. The results show that the composite has a very low thermal expansion coefficient. Thermal diffusivity decreases exponentially with temperature increase. The specific heat increases linearly as the temperature rises, and the variation trend of thermal conductivity is similar to that of thermal diffusivity. The thermal stress coefficient of C/C composite has little change with temperature variation, and thermal stress resistance of the composite at high temperature is stable.展开更多
MgO-series expansive agents can effectively compensate for the shrinkage and deformation of concrete structures.However,few experimental studies have been conducted on MgO expansive agents,particularly concerning the ...MgO-series expansive agents can effectively compensate for the shrinkage and deformation of concrete structures.However,few experimental studies have been conducted on MgO expansive agents,particularly concerning the difference between and effects of submicron-MgO and nano-MgO in high-performance concrete(HPC)with a low water-cement ratio,thereby limiting their application in practical engineering.To clarify the expansion effect and expansion mechanism of MgO expansive agents in HPC,the effects of submicron-MgO and nano-MgO on the strength,toughness,and expansion characteristics of HPC were examined.The test results showed that submicron-MgO and nano-MgO continued to hydrate in the cement environment to produce Mg(OH)_(2),thus improving the structural compactness and structural strength of HPC.Nano-MgO concrete was found to have more stable mechanical properties and better structural deformability than submicron-MgO concrete.This study provides effective data support and theoretical reference concerning the hydration expansion mechanisms and engineering applications of nano-expanded materials.展开更多
A water-swelling material is one of the rubbery impermeable materials which mixed synthetic resin elastomers as a base material, high absorbency polymers, filler and solvents. In this study, swelling characteristics o...A water-swelling material is one of the rubbery impermeable materials which mixed synthetic resin elastomers as a base material, high absorbency polymers, filler and solvents. In this study, swelling characteristics of the water-swelling material on the water polluted with COD and BOD, as an impermeable material at coastal landfill sites, are examined by laboratory swelling ratio test. Furthermore, the factor in which it influences the swelling pressure of water-swelling material is clarified by measuring the swelling pressure. As the results, the COD nor the BOD concentrations in the soaked water influence the swelling ratio of the water-swelling material. When the thicknesses of water-swelling material are 2 mm and 3 mm, the maximum swelling pressure of 0.5 MPa or more that corresponds to hydraulic pressure by depth of 50 m is possessed.展开更多
The thermophysical properties,such as thermal conductivity,thermal diffusivity,specific heat capacity and linear thermal expansion of reactive powder concrete(RPC) with different steel fiber volumetric fractions are i...The thermophysical properties,such as thermal conductivity,thermal diffusivity,specific heat capacity and linear thermal expansion of reactive powder concrete(RPC) with different steel fiber volumetric fractions are investigated by means of high temperature tests. The thermophysical characteristics of RPC with different fiber volumes under different temperatures are analyzed and compared with those of the common high-strength concrete and high-performance concrete. The empirical relationships of thermophysical properties with temperature and fiber volume are identified. By the heat transfer and solid physics methods,the microscopic physical mechanism of heat transfer process and heat conduction properties of RPC are investigated,and the theoretical formulas of specific heat capacity and thermal expansion coefficient are derived,respectively. The effects of temperature and steel fibers on the specific heat capacity and the thermal expansion coefficient are quantitatively analyzed and the discriminant conditions are provided. It is shown that the experimental results are consistent with the theoretical prediction.展开更多
Lithium(Li)metal is promising for high energy density batteries due to its low electrochemical redox potential and high specific capacity.However,the formation of dendrites and its tendency for large volume expansion ...Lithium(Li)metal is promising for high energy density batteries due to its low electrochemical redox potential and high specific capacity.However,the formation of dendrites and its tendency for large volume expansion during plating/stripping restrict the application of Li metal in practical scenarios.In this work,we developed reduced graphene oxide-graphitic carbon nitride(rGO-C3N4,GCN)with highly elastic and wrinkled structure as the current collector.Lithiophilic site C3N4 in GCN could reduce the nucleation overpotential.In addition,this material effectively inhibited electrode expansion during cycling.At the same time,due to its high elasticity,GCN could release the stress induced by Li deposition to maintain structural integrity of the electrode.Limetal anodes with GCN exhibited small volume expansion,high Coulombic efficiency(CE)of 98.6%within 300 cycles and long cycling life of more than 1700 h.This work described and demonstrated a new approach to construct flexible current collectors for stable lithium-metal anodes.展开更多
文摘The coefficient of thermal expansion, thermal diffusivity and specific heat of C/C composites from room temperature to ultra high temperature were experimentally investigated. Thermal conductivity and thermal stress resistance of the composites were therefore computed based on experimental results. The results show that the composite has a very low thermal expansion coefficient. Thermal diffusivity decreases exponentially with temperature increase. The specific heat increases linearly as the temperature rises, and the variation trend of thermal conductivity is similar to that of thermal diffusivity. The thermal stress coefficient of C/C composite has little change with temperature variation, and thermal stress resistance of the composite at high temperature is stable.
基金Project(51578325) supported by the National Natural Science Foundation of China。
文摘MgO-series expansive agents can effectively compensate for the shrinkage and deformation of concrete structures.However,few experimental studies have been conducted on MgO expansive agents,particularly concerning the difference between and effects of submicron-MgO and nano-MgO in high-performance concrete(HPC)with a low water-cement ratio,thereby limiting their application in practical engineering.To clarify the expansion effect and expansion mechanism of MgO expansive agents in HPC,the effects of submicron-MgO and nano-MgO on the strength,toughness,and expansion characteristics of HPC were examined.The test results showed that submicron-MgO and nano-MgO continued to hydrate in the cement environment to produce Mg(OH)_(2),thus improving the structural compactness and structural strength of HPC.Nano-MgO concrete was found to have more stable mechanical properties and better structural deformability than submicron-MgO concrete.This study provides effective data support and theoretical reference concerning the hydration expansion mechanisms and engineering applications of nano-expanded materials.
文摘A water-swelling material is one of the rubbery impermeable materials which mixed synthetic resin elastomers as a base material, high absorbency polymers, filler and solvents. In this study, swelling characteristics of the water-swelling material on the water polluted with COD and BOD, as an impermeable material at coastal landfill sites, are examined by laboratory swelling ratio test. Furthermore, the factor in which it influences the swelling pressure of water-swelling material is clarified by measuring the swelling pressure. As the results, the COD nor the BOD concentrations in the soaked water influence the swelling ratio of the water-swelling material. When the thicknesses of water-swelling material are 2 mm and 3 mm, the maximum swelling pressure of 0.5 MPa or more that corresponds to hydraulic pressure by depth of 50 m is possessed.
基金supported by the National Natural Science Foundation of China (Grant No. 50974125)the National Basic Research Program of China ("973" Project) (Grant Nos.2010CB226804,2002CB412705)the Beijing Key Laboratory Projects
文摘The thermophysical properties,such as thermal conductivity,thermal diffusivity,specific heat capacity and linear thermal expansion of reactive powder concrete(RPC) with different steel fiber volumetric fractions are investigated by means of high temperature tests. The thermophysical characteristics of RPC with different fiber volumes under different temperatures are analyzed and compared with those of the common high-strength concrete and high-performance concrete. The empirical relationships of thermophysical properties with temperature and fiber volume are identified. By the heat transfer and solid physics methods,the microscopic physical mechanism of heat transfer process and heat conduction properties of RPC are investigated,and the theoretical formulas of specific heat capacity and thermal expansion coefficient are derived,respectively. The effects of temperature and steel fibers on the specific heat capacity and the thermal expansion coefficient are quantitatively analyzed and the discriminant conditions are provided. It is shown that the experimental results are consistent with the theoretical prediction.
基金the National Natural Science Foundation of China(51525206 and 51927803)the National Key R&D Program of China(2016YFA0200100 and 2016YFB0100100)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22010602)Liaoning Revitalization Talents Program(XLYC1908015)China Petrochemical Cooperation(218025)。
文摘Lithium(Li)metal is promising for high energy density batteries due to its low electrochemical redox potential and high specific capacity.However,the formation of dendrites and its tendency for large volume expansion during plating/stripping restrict the application of Li metal in practical scenarios.In this work,we developed reduced graphene oxide-graphitic carbon nitride(rGO-C3N4,GCN)with highly elastic and wrinkled structure as the current collector.Lithiophilic site C3N4 in GCN could reduce the nucleation overpotential.In addition,this material effectively inhibited electrode expansion during cycling.At the same time,due to its high elasticity,GCN could release the stress induced by Li deposition to maintain structural integrity of the electrode.Limetal anodes with GCN exhibited small volume expansion,high Coulombic efficiency(CE)of 98.6%within 300 cycles and long cycling life of more than 1700 h.This work described and demonstrated a new approach to construct flexible current collectors for stable lithium-metal anodes.
