Papers by Author: Er Dong Wu

Abstract: The structures of as-cast LaNi_3.8AlMn_0.2 alloys and subsequent compounds by means of annealing at different temperature (850, 900, 950, 1000 ^oC) were examined by using neutron powder diffraction (NPD) and X-ray diffraction (XRD). Based on the Rietveld method, the diffraction data was refined using FullProf software. The refined results demonstrate the structure types of all compounds are CaCu₅ type and their space groups are P6/mmm. Increasing the annealing temperature, the lattice parameters of LaNi_3.8AlMn_0.2 compounds did not possess clearly linear variation. It is noted that Mn atoms do not occupy the 2c sites but occupy the 3g sites in all compounds.

Abstract: The intermetallic alloy LaNi_3.8AlMn_0.2 and its deuteride LaNi_3.8AlMn_0.2D_3.2 were studied by neutron powder diffraction. The experimental results show that the crystal structure of LaNi_3.8AlMn_0.2 is CaCu₅ type with the hexagonal P6/mmm space group, the substituted Al atoms occupy 2c and 3g sites, while Mn atoms are only located on the 3g sites. For the corresponding deuteride LaNi_3.8AlMn_0.2D_3.2, the P6/mmm space group gives the best refinement, but D atoms enter two interstitial sites 6m and 12n.

Abstract: Molecular dynamics (MD) techniques were employed to simulate the diffusion properties of molecular hydrogen on all-silica ZSM-5 zeolite. The results indicated that in the temperature range of 77-293K and the pressure range of 14-3360 kPa, the diffusion coefficients are found to range from 1.2×10^-9 m²/s to 3.8×10^-7 m²/s, and increase with increasing temperature, and decrease with increasing pressure. The activated energy for hydrogen diffusion determined from the simulation is pressure-dependent. The diffusion of the molecular hydrogen in all-silica ZSM-5 zeolite channels is anisotropic duo to the increase of the temperature. The diffusion coefficients in straight channels are higher than that in zigzag channels. The difference results from the structural difference of the two channels and the different loadings of hydrogen. Keywords: Hydrogen; Zeolite; Diffusion; Molecular-dynamics simulation

Abstract: A general model based on Ono-Kondo lattice theory for hydrogen adsorption, nearest neighbor interaction energy among adsorbate molecules were derived according to thermodynamic principle. A linear form of the above general model was applied to determine the interaction energies among hydrogen molecules inside adsorption layer from the previous experimental data of hydrogen adsorption on A- and X-type zeolites. The results show that the energies of hydrogen-hydrogen interactions inside the adsorption layer are negative values, indicating that the attractions among the adsorbed hydrogen molecules are prominent in the present work. And the influence of hydrogen molecules outside adsorption layer on the adsorbed hydrogen molecule is not important.

Abstract: Grand Canonical Monte Carlo (GCMC) method was employed to simulate the adsorption properties of molecular hydrogen on crossing the critical temperature in all-silica ZSM-5 zeolite in this paper. The results indicated that the adsorbed amounts of hydrogen increased with decreasing temperatures and increasing pressures. The highest hydrogen uptake value is 2.24 wt% at 25 K and 10000 kPa. By comparing the variation of the hydrogen adsorption isotherms on crossing the critical temperature, it is shown that the micropore filling and capillary condensation were the main adsorption mechanism under the critical temperature of hydrogen, and the micropore filling was the adsorption mechanism above the critical temperature. The results and data of hydrogen adsorption properties obtained from the simulations are theoretically significant for understanding of the mechanism of hydrogen storage on microporous zeolites.