In this study,we prepare the specimens of three-dimensional random fibrous(3D RF)material along its through-the-thickness(TTT)and in-plane(IP)directions.The experimental tests of tensile and compressive properties as ...In this study,we prepare the specimens of three-dimensional random fibrous(3D RF)material along its through-the-thickness(TTT)and in-plane(IP)directions.The experimental tests of tensile and compressive properties as well as fracture toughness of 3D RF material are performed at elevated temperatures.Then,the porosity(83%,87%and 89%)and temperature dependence of the tensile and compressive strength,elastic modulus,fracture toughness and fracture surface energy of the 3D RF materials for both the TTT and IP directions are analyzed.From the results of the tensile strength and elastic modulus versus material porosities at various temperatures,we find that tensile strength and elastic modulus for the TTT direction are more sensitive to the porosity,but not for the IP direction.Fracture toughness increases firstly and then decreases at a certain critical temperature.Such critical temperature is found to be the lowest for the porosity of 83%.On the other hand,at below 1073 K,the temperature-dependent fracture surface energies with three porosities for the TTT direction show similar variation trends.展开更多
Single-atom(SA)catalysts represent the ultimate limit of atom use efficiency for catalysis.Promising experimental progress in synthesizing SA catalysts aside,the atomic-scale transformation mechanism from metal nanopa...Single-atom(SA)catalysts represent the ultimate limit of atom use efficiency for catalysis.Promising experimental progress in synthesizing SA catalysts aside,the atomic-scale transformation mechanism from metal nanoparticles(NPs)to metal SAs and the stabilization mechanism of SA catalysts at high temperature remain elusive.Through systematic molecular dynamics simulations,for the first time,we reveal the atomic-scale mechanisms associated with the transformation of a metal NP into an array of stable SAs on a defective carbon surface at a high temperature,using Au as a model material.Simulations reveal the pivotal role of defects in the carbon surface in trapping and stabilizing the Au-SAs at high temperatures,which well explain previous experimental observations.Furthermore,reactive simulations demonstrate that the thermally stable Au-SAs exhibit much better catalyst activity than Au-NPs for the methane oxidation at high temperatures,in which the substantially reduced energy barriers for oxidation reaction steps are the key.Findings in this study offer mechanistic and quantitative guidance for material selection and optimal synthesis conditions to stabilize metal SA catalysts at high temperatures.展开更多
The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as ...The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as temperature increases. Above a critical temperature, β-SiC bulk just fractures after the elastic deformation. However, below the critical temperature, an interesting pattern in β-SiC bulk emerges due to the elongation of Si-C bonds before fracture. Additionally, the shear deformation of β-SiC at room temperature is found to be dependent on the strain rate. This study may shed light on the deformation mechanism dependent on temperature and strain rate.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11902046,11632014,11372238 and 11872049)the Chang Jiang Scholar Program and the 111 Project(Grant No.B18040)This work was also supported by the Fundam ental Research Funds for the Central Universities,CHD(Grant No.300102259302).
文摘In this study,we prepare the specimens of three-dimensional random fibrous(3D RF)material along its through-the-thickness(TTT)and in-plane(IP)directions.The experimental tests of tensile and compressive properties as well as fracture toughness of 3D RF material are performed at elevated temperatures.Then,the porosity(83%,87%and 89%)and temperature dependence of the tensile and compressive strength,elastic modulus,fracture toughness and fracture surface energy of the 3D RF materials for both the TTT and IP directions are analyzed.From the results of the tensile strength and elastic modulus versus material porosities at various temperatures,we find that tensile strength and elastic modulus for the TTT direction are more sensitive to the porosity,but not for the IP direction.Fracture toughness increases firstly and then decreases at a certain critical temperature.Such critical temperature is found to be the lowest for the porosity of 83%.On the other hand,at below 1073 K,the temperature-dependent fracture surface energies with three porosities for the TTT direction show similar variation trends.
文摘Single-atom(SA)catalysts represent the ultimate limit of atom use efficiency for catalysis.Promising experimental progress in synthesizing SA catalysts aside,the atomic-scale transformation mechanism from metal nanoparticles(NPs)to metal SAs and the stabilization mechanism of SA catalysts at high temperature remain elusive.Through systematic molecular dynamics simulations,for the first time,we reveal the atomic-scale mechanisms associated with the transformation of a metal NP into an array of stable SAs on a defective carbon surface at a high temperature,using Au as a model material.Simulations reveal the pivotal role of defects in the carbon surface in trapping and stabilizing the Au-SAs at high temperatures,which well explain previous experimental observations.Furthermore,reactive simulations demonstrate that the thermally stable Au-SAs exhibit much better catalyst activity than Au-NPs for the methane oxidation at high temperatures,in which the substantially reduced energy barriers for oxidation reaction steps are the key.Findings in this study offer mechanistic and quantitative guidance for material selection and optimal synthesis conditions to stabilize metal SA catalysts at high temperatures.
基金supported by the National Natural Science Foundation of China(11902243 and 51903124)the Young Elite Scientist Sponsorship Program by CAST(2019QNRC001)+2 种基金the“1000-Plan Program”of Shaanxi Provincethe“Young Talent Support Plan”of Xi’an Jiaotong UniversityInitiative Funds of Scientific Research for Metasequoia Talent(163105049)。
基金supported by the National Natural Science Foundation of China(NSFC Grants No.11632014,11302161 and11302162)China Postdoctoral Science Foundation(Grant No.2013M542339)the Chang Jiang Scholar program
文摘The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as temperature increases. Above a critical temperature, β-SiC bulk just fractures after the elastic deformation. However, below the critical temperature, an interesting pattern in β-SiC bulk emerges due to the elongation of Si-C bonds before fracture. Additionally, the shear deformation of β-SiC at room temperature is found to be dependent on the strain rate. This study may shed light on the deformation mechanism dependent on temperature and strain rate.
