An alternating current was applied to measure the impedance of a hardened cement paste with various contents of carbon fibres. When the free water content in the hardened cement paste is 90%-98%, and the measuring fr...An alternating current was applied to measure the impedance of a hardened cement paste with various contents of carbon fibres. When the free water content in the hardened cement paste is 90%-98%, and the measuring frequency 500 Hz, an approximate linear relationship was found between fibre content and impedance of the composite. Based on this relationship, a new attempt was made to evaluate the dispersion uniformity of carbon fibres in cement paste by impedance measurement. The standard deviation S and the coefficient of vriation S/X over bar //i of impedance of the fibre-cement specimens randomly taken locating in different points were used as main parameters for the uniformity assessment. As a case, four different mixing processes were designed for dispersing carbon fibres into the cement paste. The results demonstrate that the relative longer mixing time increases the dispersion uniformity of carbon fibres in cement paste, and the addition of the water reducer dramatically improves the uniformity due to the change of the fluidity of the paste. The ground fly ash can increase the uniformity to a certain extent. (Author abstract) 6 Refs.展开更多
Molecular dynamics （MD） simulation was performed to study ethene adsorption, polarization and diffusion in orthorhombic and monoclinic MFI and H[Al] ZSM-5 at 300 K. The resuits show that the interaction between ethe...Molecular dynamics （MD） simulation was performed to study ethene adsorption, polarization and diffusion in orthorhombic and monoclinic MFI and H[Al] ZSM-5 at 300 K. The resuits show that the interaction between ethene molecule and orthorhombic MFI is the strongest.Ethene molecules possess relatively low energy in the lattice of orthorhombic MFI. The existence of Al and Brnsted H atoms in the framework of H[AI]ZSM-5 can lower the energy of adsorbed ethene molecules. At the edges of intersections of channels, especially those near Al sites,ethene molecules are polarized most. Ethene molecules prefer the locations at the centers of channel intersections. The diffusion coefficients of ethene in the lattices of orthorhombic, monoclinic MFI and H[AI]ZSM-5 are 2.7 x 10<sup>-9</sup>, 2.1 x l0<sup>-9</sup>, 1.6 x 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup>, respectively. The infrared spectrum of ethene in the framework of H[Al] ZSM-5 shows five vibration peaks (v<sub>10</sub>,v<sub>7</sub>, v<sub>12</sub>, v<sub>11</sub> and V<sub>9</sub>), which is consistent with the experimental result.展开更多
文摘An alternating current was applied to measure the impedance of a hardened cement paste with various contents of carbon fibres. When the free water content in the hardened cement paste is 90%-98%, and the measuring frequency 500 Hz, an approximate linear relationship was found between fibre content and impedance of the composite. Based on this relationship, a new attempt was made to evaluate the dispersion uniformity of carbon fibres in cement paste by impedance measurement. The standard deviation S and the coefficient of vriation S/X over bar //i of impedance of the fibre-cement specimens randomly taken locating in different points were used as main parameters for the uniformity assessment. As a case, four different mixing processes were designed for dispersing carbon fibres into the cement paste. The results demonstrate that the relative longer mixing time increases the dispersion uniformity of carbon fibres in cement paste, and the addition of the water reducer dramatically improves the uniformity due to the change of the fluidity of the paste. The ground fly ash can increase the uniformity to a certain extent. (Author abstract) 6 Refs.
文摘Molecular dynamics （MD） simulation was performed to study ethene adsorption, polarization and diffusion in orthorhombic and monoclinic MFI and H[Al] ZSM-5 at 300 K. The resuits show that the interaction between ethene molecule and orthorhombic MFI is the strongest.Ethene molecules possess relatively low energy in the lattice of orthorhombic MFI. The existence of Al and Brnsted H atoms in the framework of H[AI]ZSM-5 can lower the energy of adsorbed ethene molecules. At the edges of intersections of channels, especially those near Al sites,ethene molecules are polarized most. Ethene molecules prefer the locations at the centers of channel intersections. The diffusion coefficients of ethene in the lattices of orthorhombic, monoclinic MFI and H[AI]ZSM-5 are 2.7 x 10<sup>-9</sup>, 2.1 x l0<sup>-9</sup>, 1.6 x 10<sup>-9</sup> m<sup>2</sup>·s<sup>-1</sup>, respectively. The infrared spectrum of ethene in the framework of H[Al] ZSM-5 shows five vibration peaks (v<sub>10</sub>,v<sub>7</sub>, v<sub>12</sub>, v<sub>11</sub> and V<sub>9</sub>), which is consistent with the experimental result.
