Showing papers by "Hua Zhang published in 1996"
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TL;DR: A pyrazolate-bridged tetranuclear copper(II) complex was synthesized and its crystal structure determined in this article, which consists of four copper atoms bridged by four planar L ligands through the nitrogen atoms of the pyrazole groups to form a (CuL(H2O))4 12-membered ring.
Abstract: A new pyrazolate-bridged tetranuclear copper(II) complex [{CuL(H2O)}4]·12H2O (H2L = 5-methoxycarbonylpyrazole-3-carboxylic acid) was synthesized and its crystal structure determined. The molecule has C2 symmetry and consists of four copper atoms bridged by four planar L ligands through the nitrogen atoms of the pyrazole groups to form a (–Cu–N–N–)4 12-membered ring. The co-ordination of each copper is distorted square planar. The basal plane of each copper atom is nearly parallel to a neighbouring pyrazole plane and perpendicular to another neighbouring pyrazole plane. In the crystal there is a hydrogen-bond network between water molecules and carboxylate groups which may control the packing. The magnetic properties of the complex have also been investigated down to 5 K. The fitting of the experimental data using a Heisenberg Hamiltonian shows that the exchange interaction between the copper atoms propagated through the monopyrazolate bridge is antiferromagnetic with J=–12.34 cm–1. The reason for this small value relative to those in di-µ-pyrazolato-dicopper(II) complexes is discussed.
31 citations
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TL;DR: In this article, the effects of water flow rate (WFR) and length of air gap (LAG) on the characteristics of hollow fiber membranes produced by the solution spinning technique using two polymer solution compositions C1 and C2, were studied experimentally.
Abstract: The effects of water flow rate (WFR) (5 or 7.5 mL/min) and length of air gap (LAG) (in the range of 50 to 120 cm) on the characteristics of hollow fiber membranes produced by the solution spinning technique using two polymer solution compositions C1 and C2, were studied experimentally. The polymer (polyethersulfone), solvent (1-methyl-2-pyrrolidone), and additive (polyvinyl pyrrolidone) concentrations (wt%) were 20, 75, and 5 respectively for the C1 solution, and 20, 70, and 10 respectively for the C2 solution. The viscosity of the C1 solution used was 2112 cP and that of the C2 solution used was 3924 cP. The extrusion pressures (EP) were 5 and 15 psig, respectively, for fiber production from the C1 and C2 solutions. The effect of higher solution viscosity, together with higher EP, was to increase both the outside diameter (OD) and the inside diameter (ID) for C2 fibers. For both C1 and C2 fibers, an increase in WFR at a given LAG tended to increase OD and ID and to decrease wall thickness, where...
30 citations
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TL;DR: In this paper, the same grain boundaries were examined by transmission electron microscopy and high-resolution electron microscope and it was found that the boundaries are for the most part free of precipitates and well structured at the atomic scale.
Abstract: Tilt grain-boundary junctions with a 45° [001] misorientation were formed in YBa 2 Cu 3 O 7− x (YBCO) thin films grown by pulsed organometallic beam epitaxy on (100) MgO substrates. The junctions were introduced at predetermined locations due to a modification of the orientation relation between the thin film and substrate following a low-energy argon ion irradiation of specific areas of the substrate surface prior to film deposition. Rutherford backscatter spectrometry and certain surface features observed by atomic force microscopy indicate that implantation of ions is necessary to cause the modified epitaxy. The low-temperature transport characteristics of individual isolated grain boundaries were determined by electromagnetic characterizations of the junction behavior. The same grain boundaries were examined by transmission electron microscopy and high-resolution electron microscopy and it was found that the boundaries are for the most part free of precipitates and well structured at the atomic scale. Regardless of the average grain boundary inclination, asymmetric (110)(100) facets dominate the microstructure of the junctions. Possible mechanisms for epitaxy modification and the transport properties in relation to the observed microstructure are discussed.
10 citations