The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) sim'lation. It was found that the hydrogen molecules distribute regularly inside and outside of the tu...The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) sim'lation. It was found that the hydrogen molecules distribute regularly inside and outside of the tube. Density distribution was computed for H2 molecule. Theoretical analysis of the result showed the multilayer adsorption mechanism of SWCNTs. The storage of H2 in SWCNTs is computed, which provides essential theoretical reference for further study of hydrogen adsorption in SWCNTs.展开更多
Compared chemical bonds change situation of coal surface and oxygen mole- cules before and after coal surface adsorption to three oxygen molecules,after adsorption each oxygen molecule's chemical bond got longer,b...Compared chemical bonds change situation of coal surface and oxygen mole- cules before and after coal surface adsorption to three oxygen molecules,after adsorption each oxygen molecule's chemical bond got longer,but had not broken,the coal surface's chemical bonds changed a little.It proves that the coal surface adsorption to five oxygen molecules is the physical adsorption and is the multilayer adsorption according to the op- timized geometry structure.The oxygen molecule's bond length that adsorbed by the side chain of coal surface changes most from 1.258 2×10^(-10) m to 1.316 8×10^(-10) m,which indi- cates this oxygen molecular to be the liveliest.The analysis of charge population reveals that how many electrons shift in the atom is directly proportional to the change of chemical bonds.The more electrons shift in the atom,the more molecule chemical bond changes. In the adsorption state,which is composed of coal surface and five oxygen molecules,the vibration frequency of oxygen molecules drops off,and the adsorption energy reached by calculation is 202.11 kJ/mol.展开更多
The surface adsorption of gas molecules is a key factor limiting the secondary electron yield(SEY)of a material in many areas of applied physics.The influence of O_(2)adsorption on the SEY of metallic Ag is investigat...The surface adsorption of gas molecules is a key factor limiting the secondary electron yield(SEY)of a material in many areas of applied physics.The influence of O_(2)adsorption on the SEY of metallic Ag is investigated in this work.To account for the particle distribution,we propose a BET theory based on multilayer O_(2)physisorption model.Furthermore,based on the phenomenological model of secondary electron(SE)emission and by taking into account the different scattering processes between electrons and particles in the adsorbed layer,we develop a numerical model of SEY in the adsorbed state using Monte Carlo simulations.The relationships among O_(2)adsorption,adsorption layer thickness,and SEY variation characteristics are then examined through a series of experiments.After 12-h exposure to O_(2),the clean samples increases12%-19%of the maximum value of SEY and 2.3 nm in thickness of the adsorbed layer.Experimental results are also compared with the results from the MC model to determine whether the model is accurate.展开更多
Gas adsorption-induced coal swelling is a well- know phenomenon. Coal swelling or shrinkage by adsorption or desorption of water vapor has not been well understood but has significant implications on gas drainage proc...Gas adsorption-induced coal swelling is a well- know phenomenon. Coal swelling or shrinkage by adsorption or desorption of water vapor has not been well understood but has significant implications on gas drainage process for underground coal mining and for primary and enhanced combed methane production. Decreased matrix moisture content leads to coal shrinkage and thus the change of cleat porosity and permeability under reservoir conditions. Unlike gas adsorption in coal which usually forms a single layer of adsorbed molecules, water vapor adsorption in the coal micropores forms multilayer of adsorbed molecules. In this work, a model has been developed to describe the coal swelling strain with respect to the amount of moisture intake by the coal matrix. The model extended an energy balance approach for gas adsorption-induced coal swelling to water vapor adsorption-induced coal swelling, assuming that only the first layer of adsorbed molecules of the multilayer adsorption changes the surface energy, which thus causes coal to swell. The model is applied to describe the experimental swelling strain data measured on an Aus- tralian coal. The results show good agreement between the model and the experimental data.展开更多
文摘The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) sim'lation. It was found that the hydrogen molecules distribute regularly inside and outside of the tube. Density distribution was computed for H2 molecule. Theoretical analysis of the result showed the multilayer adsorption mechanism of SWCNTs. The storage of H2 in SWCNTs is computed, which provides essential theoretical reference for further study of hydrogen adsorption in SWCNTs.
基金National Natural Science Foundation(50474010)Eleventh Five Year Key Technologies(2006BAK03B05)
文摘Compared chemical bonds change situation of coal surface and oxygen mole- cules before and after coal surface adsorption to three oxygen molecules,after adsorption each oxygen molecule's chemical bond got longer,but had not broken,the coal surface's chemical bonds changed a little.It proves that the coal surface adsorption to five oxygen molecules is the physical adsorption and is the multilayer adsorption according to the op- timized geometry structure.The oxygen molecule's bond length that adsorbed by the side chain of coal surface changes most from 1.258 2×10^(-10) m to 1.316 8×10^(-10) m,which indi- cates this oxygen molecular to be the liveliest.The analysis of charge population reveals that how many electrons shift in the atom is directly proportional to the change of chemical bonds.The more electrons shift in the atom,the more molecule chemical bond changes. In the adsorption state,which is composed of coal surface and five oxygen molecules,the vibration frequency of oxygen molecules drops off,and the adsorption energy reached by calculation is 202.11 kJ/mol.
基金Project supported by the Fund from the National Key Laboratory of Science and Technology on Space Mircrowave,China(Grant No.6142411112205)the National Natural Science Foundation of China(Grant No.62001376)。
文摘The surface adsorption of gas molecules is a key factor limiting the secondary electron yield(SEY)of a material in many areas of applied physics.The influence of O_(2)adsorption on the SEY of metallic Ag is investigated in this work.To account for the particle distribution,we propose a BET theory based on multilayer O_(2)physisorption model.Furthermore,based on the phenomenological model of secondary electron(SE)emission and by taking into account the different scattering processes between electrons and particles in the adsorbed layer,we develop a numerical model of SEY in the adsorbed state using Monte Carlo simulations.The relationships among O_(2)adsorption,adsorption layer thickness,and SEY variation characteristics are then examined through a series of experiments.After 12-h exposure to O_(2),the clean samples increases12%-19%of the maximum value of SEY and 2.3 nm in thickness of the adsorbed layer.Experimental results are also compared with the results from the MC model to determine whether the model is accurate.
文摘Gas adsorption-induced coal swelling is a well- know phenomenon. Coal swelling or shrinkage by adsorption or desorption of water vapor has not been well understood but has significant implications on gas drainage process for underground coal mining and for primary and enhanced combed methane production. Decreased matrix moisture content leads to coal shrinkage and thus the change of cleat porosity and permeability under reservoir conditions. Unlike gas adsorption in coal which usually forms a single layer of adsorbed molecules, water vapor adsorption in the coal micropores forms multilayer of adsorbed molecules. In this work, a model has been developed to describe the coal swelling strain with respect to the amount of moisture intake by the coal matrix. The model extended an energy balance approach for gas adsorption-induced coal swelling to water vapor adsorption-induced coal swelling, assuming that only the first layer of adsorbed molecules of the multilayer adsorption changes the surface energy, which thus causes coal to swell. The model is applied to describe the experimental swelling strain data measured on an Aus- tralian coal. The results show good agreement between the model and the experimental data.
