Silica sources influence different aspects of Al-MCM-41 product. The crystallinity of nanosized Al-MCM-41 zeolites prepared crystallization and lead to change in the properties of the final from precursors mixtures co...Silica sources influence different aspects of Al-MCM-41 product. The crystallinity of nanosized Al-MCM-41 zeolites prepared crystallization and lead to change in the properties of the final from precursors mixtures containing different silica sources, e.g. tetraethylorthosilicate （TEOS）, colloidal silica （CS）, silicic acid （SA） and fumed silica （FS） have been studied. The produced samples are investigated using XRD, SEM, FT-IR, pyridine adsorption and N2 physisorption. XRD results show that the products obtained from different silica sources are in Al-MCM-41 phase. SEM results show that silica sources influence the produced Al-MCM-41 shape. Using silicic acid leads to formation of spherical crystals, TEOS gives cubical crystals, colloidal silica forms spherical crystals with smaller aggregated, and fumed silica gives rounded crystals. N2 physisorption results show that silica sources influence pore-diameter and pore-volume of the produced Al-MCM-41 ; the pore diameter of the produced Al-MCM-41 in case of colloidal silica, TEOS, fumed silica, and silicic acid are 12, 20, 15, and 17A respectively. Also, the pore volume of the produced AI-MCM-41 in case of colloidal silica, TEOS, fumed silica and silicic acid are 0.78, 0.71, 0.76, and 0.8 cm^3/gm, respectively.展开更多
The first-principles study of the structural, elastic and electronic properties of the M2XC phases depending on the type of M transition metal （M are Ti and Cr） and on X （X are Ga and A1） was reported. The calcula...The first-principles study of the structural, elastic and electronic properties of the M2XC phases depending on the type of M transition metal （M are Ti and Cr） and on X （X are Ga and A1） was reported. The calculations are performed using the pseudo-potential plane-wave approach in both the local density and generalized gradient approximations. The elastic constants are calculated using the static finite strain technique. Features such as structural and elastic parameters, Debye tem- perature, sound velocities and their pressure dependence have been investigated. In agreement with experimental and previous theoretical findings, it is found that the compressibility along a and c axis depends on the valence electron concentration （VEC）. Correlations revealing the governing role of the X and M elements on the machinability indices of the material have been examined. The electronic properties have been discussed in terms of chemical bonding showing that bonding is due to Md-Cp and Md-Xp hybridizations. M-C bonds are stiffer than M-X ones and A1-Ti （Cr-C） bonds are stiffer than those corresponding to Ti-C （A1-Cr）. It is shown that the stiffness of the M-X and M-C bonds increases with increasing the number of VEC.展开更多
文摘Silica sources influence different aspects of Al-MCM-41 product. The crystallinity of nanosized Al-MCM-41 zeolites prepared crystallization and lead to change in the properties of the final from precursors mixtures containing different silica sources, e.g. tetraethylorthosilicate （TEOS）, colloidal silica （CS）, silicic acid （SA） and fumed silica （FS） have been studied. The produced samples are investigated using XRD, SEM, FT-IR, pyridine adsorption and N2 physisorption. XRD results show that the products obtained from different silica sources are in Al-MCM-41 phase. SEM results show that silica sources influence the produced Al-MCM-41 shape. Using silicic acid leads to formation of spherical crystals, TEOS gives cubical crystals, colloidal silica forms spherical crystals with smaller aggregated, and fumed silica gives rounded crystals. N2 physisorption results show that silica sources influence pore-diameter and pore-volume of the produced Al-MCM-41 ; the pore diameter of the produced Al-MCM-41 in case of colloidal silica, TEOS, fumed silica, and silicic acid are 12, 20, 15, and 17A respectively. Also, the pore volume of the produced AI-MCM-41 in case of colloidal silica, TEOS, fumed silica and silicic acid are 0.78, 0.71, 0.76, and 0.8 cm^3/gm, respectively.
文摘The first-principles study of the structural, elastic and electronic properties of the M2XC phases depending on the type of M transition metal （M are Ti and Cr） and on X （X are Ga and A1） was reported. The calculations are performed using the pseudo-potential plane-wave approach in both the local density and generalized gradient approximations. The elastic constants are calculated using the static finite strain technique. Features such as structural and elastic parameters, Debye tem- perature, sound velocities and their pressure dependence have been investigated. In agreement with experimental and previous theoretical findings, it is found that the compressibility along a and c axis depends on the valence electron concentration （VEC）. Correlations revealing the governing role of the X and M elements on the machinability indices of the material have been examined. The electronic properties have been discussed in terms of chemical bonding showing that bonding is due to Md-Cp and Md-Xp hybridizations. M-C bonds are stiffer than M-X ones and A1-Ti （Cr-C） bonds are stiffer than those corresponding to Ti-C （A1-Cr）. It is shown that the stiffness of the M-X and M-C bonds increases with increasing the number of VEC.
