致密气在α-SiO_2(010)面吸附的第一性原理研究

致密气在砂岩储层中的赋存状态一直是人们研究的热点.为了论证致密气在石英砂岩表面吸附性的强弱,基于密度泛函理论的第一性原理方法,以CH_4分子为主要研究对象,研究了CH_4、C_2H_6、CO_2、N_2分子在α-SiO_2(010)面的吸附性质.结果表明:CH_4、C_2H_6、CO_2、N_2分子在α-SiO_2(010)面的吸附能力从小到大依次为CO_2N_2CH_4C_2H_6,其中CH_4分子在B12位的吸附能最低,为-0.5379 eV,几何结构变化最小,吸附最稳定,是一种物理吸附;烃类气体的吸附性比非烃类的吸附性强;不同高对称位的吸附能变化范围很小,气体在α-SiO_2(010)面的流动性很强;在B12位吸附后,CH_4分子的s态、p态电子密度整体向低能量区域偏移约3.2 eV,而α-SiO_2(010)表面硅原子的电子态密度曲线几乎不变.     

Density functional theory study of structural stability for gas hydrate

Using the first-principles method based on the density functional theory(DFT),the structures and electronic properties of different gas hydrates(CO_2,CO,CH_4,and H_2) are investigated within the generalized gradient approximation.The structural stability of methane hydrate is studied in this paper.The results show that the carbon dioxide hydrate is more stable than the other three gas hydrates and its binding energy is-2.36 e V,and that the hydrogen hydrate is less stable and the binding energy is-0.36 e V.Water cages experience repulsion from inner gas molecules,which makes the hydrate structure more stable.Comparing the electronic properties of two kinds of water cages,the energy region of the hydrate with methane is low and the peak is close to the left,indicating that the existence of methane increases the stability of the hydrate structure.Comparing the methane molecule in water cages and a single methane molecule,the energy of electron distribution area of the former is low,showing that the filling of methane enhances the stability of hydrate structure.     

Molecular dynamics simulation of decomposition and thermal conductivity of methane hydrate in porous media

The hydrate has characteristics of low thermal conductivity and temperature sensitivity. To further analysis the mechanism of thermal conductivity and provide method for the exploitation, transportation and utilization of hydrate, the effect of decomposition and thermal conductivity of methane hydrate in porous media has been studied by using the molecular dynamics simulation. In this study, the simulation is carried out under the condition of temperature 253.15 K-273.15 K and pressure 1 MPa. The results show that the thermal conductivity of methane hydrate increases with the increase of temperature and has a faster growth near freezing. With the addition of porous media, the thermal conductivity of the methane hydrate improves significantly. The methane hydrate-porous media system also has the characteristics of vitreous body.With the decrease of the pore size of the porous media, thermal conductivity of the system increases gradually at the same temperature. It can be ascertained that the porous media of different pore sizes have strengthened the role of the thermal conductivity of hydrates.     

体育器材中碳纤维材料的密度泛函理论研究

基于密度泛函理论的第一性原理方法,研究了掺杂对碳纤维性质影响的微观机理.对碳纤维掺杂结构、电子性质及弹性模量进行分析,得出如下结论:Ⅰ型掺杂时碳纤维的形成能范围在4.79~20.03eV,Ⅱ型掺杂时的形成能在4.31~22.36eV.2种掺杂模型掺杂后结构未见明显变化,只是键长与层间距发生变化,由范德华力作用耦合C原子与不同原子半径的原子相互作用所导致.Ⅰ型Mg掺杂碳纤维后a方向的模量增加了2 833.11Gpa,Ⅱ型Mg掺杂时提升2 436.03GPa,Ⅰ型Al掺杂碳纤维后a方向的模量增加了1 624.86Gpa,弹性模量增长非常明显.对弹性模量明显增长的掺杂模型进行电子态密度分析,结果表明Al,Mg掺杂碳纤维结构在高弹性模量要求下更加稳定.由此可得,碳纤维材料中掺杂Al和Mg可以提高碳纤维材料弹性性能.