In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be（0001） surface. In our calculations, the adsorb...In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be（0001） surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of - 437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3al-like molecular orbital with the （s, P2） orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the lbz-like orbital of the H2O molecule plays a dominant role.展开更多
Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional ...Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.展开更多
The surface structures ofwurtzite ZnO（0001） and（0001） surfaces are investigated by using a first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density functional theory（DFT...The surface structures ofwurtzite ZnO（0001） and（0001） surfaces are investigated by using a first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density functional theory（DFT）.The calculated results reveal that the surface energy of ZnO-Zn is bigger than that of ZnO-O,and the ZnO-Zn surface is more unstable and active.These two surfaces are apt to relax inward,but the contractions of the ZnO-Zn surface are smaller than the ZnO-O surface.Due to the dispersed Zn4s states and the states of stronger hybridization between the Zn and O atoms,the ZnO-Zn surface shows n-type conduction,while the O2p dangling-bond bands in the upper part of the valence cause the ZnO-O surface to have p-type conduction.The above results are broadly consistent with the experimental results.展开更多
High-energy micro-arc alloying (HEMAA) is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse dura...High-energy micro-arc alloying (HEMAA) is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse durations of a few microseconds combined with pulse frequencies in the 0.1 to 2-kilohertz range thus allow substrate heat dissipation over ～99% of the duty cycle while heating only about 1%.The cooling rates may approach 105 to 106 ℃/s,depending on material.This obtained coating can produce unique corrosion and tribological benefits.Substrates require no special surface preparation and nearly any metal,alloy or cermets can be applied to metal surfaces.This paper details experimental results when alloying Mg base alloy ZM5,using Mg-Y electrodes with a water-based dielectric fluid.The morphology and the composition of the alloying was analyzed by scanning electron microscope(SEM) and energy dispersive X-ray analysis(EDX).At the discharge energies employed,a thin recast layer thickness and rougher layers were formed on the surface.All layers were in general discontinuous.EDX analysis showed that the Y transferred from the solid electrodes to the workpiece surface.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11074217)
文摘In this paper, the density functional theory has been used to perform a comparative theoretical study of water monomer, dimer, trimer, and bilayer adsorptions on the Be（0001） surface. In our calculations, the adsorbed water molecules are energetically favoured adsorbed on the atop sites, and the dimer adsorption is found to be the most stable with a peak adsorption energy of - 437 meV. Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3al-like molecular orbital with the （s, P2） orbitals of the surface beryllium atoms. While in the case of the water dimer adsorption, the lbz-like orbital of the H2O molecule plays a dominant role.
基金Supported by Hunan Provincial Innovation Foundation for Postgraduate (521298294)Natural Science Foundation of Hunan Province (09JJ6079)Program for Changjiang Scholars and the Innovative Research Team in University (531105050037)
基金Project (51201079) supported by the National Natural Science Foundation of ChinaProject (2012Z099) supported by the Scientific Research Fund of Department of Education of Yunnan Province,ChinaProject (KKSY201251033) supported by the Scientific Research Foundation for Introduced Talents of KMUST,China
基金Supported by the PhD Programs Foundation of Ministry of Education of China(Grant No.200805321032)the Science and Technology Program Project of Hunan Province(Grant No.2008GK3083)the Program for Changjiang Scholars and the Innovative Research Team in university(Grant No.531105050037)
文摘Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (EF)) at Fermi level and more bonding elec- trons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface.
基金Project supported by the National Natural Science Foundation of China(No.60877069)the Research Project of Science and Technology of Guangzhou,Guangdong Province,China(Nos.2007A010500011,2008B010200041).
文摘The surface structures ofwurtzite ZnO（0001） and（0001） surfaces are investigated by using a first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density functional theory（DFT）.The calculated results reveal that the surface energy of ZnO-Zn is bigger than that of ZnO-O,and the ZnO-Zn surface is more unstable and active.These two surfaces are apt to relax inward,but the contractions of the ZnO-Zn surface are smaller than the ZnO-O surface.Due to the dispersed Zn4s states and the states of stronger hybridization between the Zn and O atoms,the ZnO-Zn surface shows n-type conduction,while the O2p dangling-bond bands in the upper part of the valence cause the ZnO-O surface to have p-type conduction.The above results are broadly consistent with the experimental results.
基金Foundation item:National Nature Science Foundation of China(50801050)
文摘High-energy micro-arc alloying (HEMAA) is a consumable electrode,micro-welding process which uses electrical pulses that are typically three orders of magnitude shorter than in other pulse welding processes.Pulse durations of a few microseconds combined with pulse frequencies in the 0.1 to 2-kilohertz range thus allow substrate heat dissipation over ～99% of the duty cycle while heating only about 1%.The cooling rates may approach 105 to 106 ℃/s,depending on material.This obtained coating can produce unique corrosion and tribological benefits.Substrates require no special surface preparation and nearly any metal,alloy or cermets can be applied to metal surfaces.This paper details experimental results when alloying Mg base alloy ZM5,using Mg-Y electrodes with a water-based dielectric fluid.The morphology and the composition of the alloying was analyzed by scanning electron microscope(SEM) and energy dispersive X-ray analysis(EDX).At the discharge energies employed,a thin recast layer thickness and rougher layers were formed on the surface.All layers were in general discontinuous.EDX analysis showed that the Y transferred from the solid electrodes to the workpiece surface.
