Effect of exchangeable cation on the swelling property of 2:1 dioctahedral smectite--a periodic first principle study

We used both localized and periodic calculations on a series of monovalent (Li+, Na+, K+, Rb+, Cs+) and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations to monitor their effect on the swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied: Ca2+ > Sr2+ > Mg2+ > Rb+ > Ba2+ > Na+ > Li+ > Cs+ > K+. We have shown that, in case of dioctahedral smectite, the hydroxyl groups play a major role in their interaction with water and other polar molecules in the presence of an interlayer cation. We studied both type of clays, with a different surface structure and with/without water using a periodic calculation. Interlayer cations and charged 2:1 clay surfaces interact strongly with polar solvents; when it is in an aqueous medium, clay expands and the phenomenon is known as crystalline swelling. The extent of swelling is controlled by a balance between relatively strong swelling forces and electrostatic forces of attraction between the negatively charged phyllosilicate layer and the positively charged interlayer cation. We have calculated the solvation energy at the first hydration shell of an exchangeable cation, but the results do not correspond directly to the experimental d-spacing values. A novel quantitative scale is proposed with the numbers generated by the relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions within the helm of the hard soft acid base principle. The solvation effect thus measured show a perfect match with experiment, which proposes that the reactivity index calculation with a first hydration shell could rationalize the swelling mechanism for exchangeable cations. The conformers after electron donation or acceptance propose the swelling mechanism for monovalent and divalent cations.     

Two-way coupling of Eulerian–Lagrangian model for dispersed multiphase flows using filtering functions

Eulerian–Lagrangian approaches for dispersed multiphase flows can simulate detailed flow structures with a much higher spatial resolution than the Eulerian–Eulerian approaches. However, there are still unsolved problems regarding the calculation method for accurate two-way interaction, especially on the numerical instability due to the dispersion migration through discrete computational grids. Inadequate solvers sometimes produce false velocity fluctuation which makes the simulation unstable. In this paper, a new calculation method for dispersion-to-continuous phase interaction, which is accompanied by spherical dispersion migration, is proposed. The basic principle of the method is the introduction of Lagrangian filtering functions which convert discrete dispersion volume fractions to a spatially differentiable distribution. The performance of linear, Gaussian and sinewave filtering functions is examined by simple benchmark tests and applied to the simulation of dispersion-generated fluctuation. Using the present method, three-dimensional continuous phase flow structures induced by rising spherical bubbles and/or settling solid particles are demonstrated.     

采用PTV技术研究循环流化床内气固两相流动

采用PTV技术对循环流化床顶部颗粒稀疏流动区域进行了测量，其中采用先进的高速摄像技术获取流动的连续图像，并采用目前有望在气固两相流动测量中发挥较大作用的四种PTV算法：BICC法、VGT法、SPRING法和4-FRAME法，对所获取的图像进行颗粒配对处理，从而得到流场中运动颗粒的速度信息。所得到的结论为：本文所采用的PTV算法在图像处理中都产生少量的伪矢量，通过采取简单的伪矢量识别算法就可以剔除大部分伪矢量；本文实验条件下，测得循环流化床顶部区域内颗粒运动速度差别较小。本文工作为进一步详细实验测量研究奠定了理论与技术基础。     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

Resonant two photon spectrum in a Doppler broadened line

The line shape in the resonant and near resonant two photon absorption spectra in the $\text{Na 3S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?3P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?5S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ transition was investigated using two single frequency dye lasers. Two types of Doppler-free peaks for resonant case and Doppler-broadened normal two photon peaks were observed. They were different in the width, selection rule and the laser power dependence in agreement with theory.     

Photoisomerization of 1,2-diphenylcyclopropane sensitized by polypeptides containing naphthalene groups in their side chain

Poly(γ-1-naphthylmethyl L - and DL -glutamate) (PNLG and PNDLG) and copolypeptides of γ-1-naphthylmethyl L -glutamate and γ-benzyl-L -glutamate were used as sensitizers for isomerization of trans-1,2-diphenylcyclopropane. Quantum yields relative to that of 1-methylnaphthalene were measured in dichloroethane (DCE) and dichloroacetic acid (DCA). The relative quantum yield in DCE was smaller than unity for PNLG, but greater than unity for PNDLG and copolypeptides. The result is discussed in terms of increased effective collisional radius and energy trapping by excimer formation. The relative quantum yields in DCA were close to unity except for the copolypeptides of higher γ-benzyl L -glutamate content. This suggests that the naphthalene groups act in the same manner as their monomeric counterparts in the random conformation and that the greater proportion of γ-benzyl L -glutamate in the copolypeptides lowers the quantum efficiency because trans-1,2-diphenylcyclopropane must penetrate through the polymeric medium in order to encounter the excited naphthalene.     

Frequency dependence of the spin-lattice relaxation time in solid H2 with very low concentration of ortho-molecules

By extending the previous theory of Hama et al. for the spectral density in the system of randomly distributed spins with R^–n-interactions, the frequency dependence of the spin-lattice relaxation time of o-H₂ in solid H₂ at very low concentration is studied, with results in excellent agreement with measurements. In the present extension the effects of the anisotropy and rotational Zeeman energies have been taken into account by the use of the measured constants relevant to both energies.     

Preparation of “pore-fill” type Pd–YSZ–γ-Al2O3 composite membrane supported on α-Al2O3 tube for hydrogen separation

Mesoporous YSZ–γ-Al₂O₃ membranes were coated on α-Al₂O₃ (Ø2 mm) tube by dipping the α-Al₂O₃ support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al₂O₃ support. The quality of the mesoporous YSZ–γ-Al₂O₃ membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al₂O₃ content became more than 40%. Addition of γ-Al₂O₃ inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N₂ permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al₂O₃ layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al₂O₃ composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al₂O₃ layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H₂ flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al₂O₃ by elevation of temperature.