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891.
Electric discharge phenomena in metal–solvent mixtures are investigated utilizing a high field density, sealed-vessel, single-mode 2.45 GHz microwave reactor with a built-in camera. Particular emphasis is placed on studying the discharges exhibited by different metals (Mg, Zn, Cu, Fe, Ni) of varying particle sizes and morphologies in organic solvents (e.g., benzene) at different electric field strengths. Discharge phenomena for diamagnetic and paramagnetic metals (Mg, Zn, Cu) depend strongly on the size of the used particles. With small particles, short-lived corona discharges are observed that do not lead to a complete breakdown. Under high microwave power conditions or with large particles, however, bright sparks and arcs are experienced, often accompanied by solvent decomposition and formation of considerable amounts of graphitized material. Small ferromagnetic Fe and Ni powders (<40 μm) are heated very rapidly in benzene suspensions and start to glow in the microwave field, whereas larger particles exhibit extremely strong discharges. Electric discharges were also observed when Cu metal or other conductive materials such as silicon carbide were exposed to the microwave field in the absence of a solvent in an argon or nitrogen atmosphere. 相似文献
892.
Konrad Güth Julia Lyubina Bernhard Gebel Ludwig Schultz Oliver Gutfleisch 《Journal of magnetism and magnetic materials》2012
This paper reports on the grain refinement in dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) processed Nd-rich Nd2Fe14B and stoichiometric Nd2Fe14B powders using high pressure reactive milling (HPRM) followed by a subsequent desorption and recombination. In contrast to the dynamic-HDDR processed anisotropic powder with a grain size of the Nd2Fe14B phase of 300 nm, the new approach yields a further reduction of the Nd2Fe14B1 grain size to less than 70 nm. Nd-rich Nd2Fe14B powder produced by HPRM and subsequent desorption exhibits a coercivity μ0iHc=1.35 T and a remanence of 0.80 T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85 T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd2Fe14B powders. 相似文献
893.
Pacheco-Contreras R Dessens-Félix M Borbón-González DJ Paz-Borbón LO Johnston RL Schön JC Posada-Amarillas A 《The journal of physical chemistry. A》2012,116(21):5235-5239
The threshold method is used to explore the potential energy surface of the Pt(1)Pd(12) bimetallic cluster, defined by the Gupta semiempirical potential. A set of helical structures, which follow a Bernal tetrahelix pattern, correspond to local minima for the Pt(1)Pd(12) cluster, characterizing the region of the energy landscape where these structures are present. Both right-handed and left-handed chiral forms were discovered in our searches. Energetic and structural details of each of the tetrahelices are reported as well as the corresponding transition probabilities between these structures and with respect to the icosahedron-shaped global minimum structure via a disconnectivity graph analysis. 相似文献
894.
OO Adeyemi VL Malinovskii SM Biner G Calzaferri R Häner 《Chemical communications (Cambridge, England)》2012,48(77):9589-9591
A light-harvesting system based on a DNA-organized oligopyrene-cyanine complex is described. Energy transfer from the pyrene units to the cyanine dye was found to proceed via FRET from locally confined excimers to the acceptor. 相似文献
895.
T Marshall-Roth SC Liebscher K Rickert NJ Seewald AG Oliver SN Brown 《Chemical communications (Cambridge, England)》2012,48(63):7826-7828
Mechanistic studies indicate that the oxomolybdenum(vi) bis(3,5-di-tert-butylcatecholate) fragment deoxygenates pyridine-N-oxides in a reaction where the oxygen is delivered to molybdenum but the electrons for substrate reduction are drawn from the bound catecholate ligands, forming 3,5-di-tert-butyl-1,2-benzoquinone. 相似文献
896.
JA Paquette CJ Yardley KM Psutka MA Cochran O Calderon VE Williams KE Maly 《Chemical communications (Cambridge, England)》2012,48(66):8210-8212
We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges. 相似文献
897.
The first enantioselective synthesis of (-)-paeonilide is reported. Starting from inexpensive furan-3-carboxylic acid the targeted monoterpene was obtained in 12 steps via an asymmetric cyclopropanation-lactonization cascade and a stereoselective side chain insertion at an acetal-like position. 相似文献
898.
All-atom molecular dynamics computer simulations were used to blindly predict the hydration free energies of a range of chloro-organic compounds as part of the SAMPL3 challenge. All compounds were parameterized within the framework of the OPLS-AA force field, using an established protocol to compute the absolute hydration free energy via a windowed free energy perturbation approach and thermodynamic integration. Three different approaches to deriving partial charge parameters were pursued: (1) using existing OPLS-AA atom types and charges with minor adjustments of partial charges on equivalent connecting atoms; (2) calculation of quantum mechanical charges via geometry optimization, followed by electrostatic potential (ESP) fitting, using Jaguar at the LMP2/cc-pVTZ(-F) level; and (3) via geometry optimization and CHelpG charges (Gaussian03 at the HF/6-31G* level), followed by two-stage RESP fitting. Protocol 3 generated the most accurate predictions with a root mean square (RMS) error of 1.2 kcal mol(-1) for the entire data set. It was found that the deficiency of the standard OPLS-AA parameters, protocol 1 (RMS error 2.4 kcal mol(-1) overall), was mostly due to compounds with more than three chlorine substituents on an aromatic ring. For this latter subset, the RMS errors were 1.4 kcal mol(-1) (protocol 3) and 4.3 kcal mol(-1) (protocol 1), respectively. We propose new OPLS-AA atom types for aromatic carbon and chlorine atoms in rings with ≥4 Cl-substituents that perform better than the best QM-based approach, resulting in an RMS error of 1.2 kcal mol(-1) for these difficult compounds. 相似文献
899.
Oliver Osters Tom Nilges Michael Schoeneich Peer Schmidt Jan Rothballer Florian Pielnhofer Richard Weihrich 《ChemInform》2012,43(43):no-no
The title compound, the first intermetallic compound in the Cu—Cd—As system, is synthesized by solid state reaction of a stoichiometric mixture of the elements (1000 °C, 63 h) and characterized by powder and single crystal XRD, DFT electronic structure calculations, and magnetic measurements. 相似文献
900.
Schneider MN Fahrnbauer F Rosenthal T Döblinger M Stiewe C Oeckler O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(4):1209-1218
The isostructural phases 39R‐Ge0.067Sb0.667Te0.266 (R$\bar 3The isostructural phases 39R-Ge(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2649(1), c=75.061(2) ?) and 39R-Sn(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2959(1), c=75.392(2) ?) were prepared by quenching stoichiometric melts of the pure elements and subsequent annealing at moderate temperatures. Their structures are comparable to "superlattices" synthesized by layer-by-layer deposition onto a substrate. These structures show no stacking disorder by electron microscopy. The structure of the metastable layered phases are similar to that of 39R-Sb(10)Te(3) (equivalent to Sb(0.769)Te(0.231)), which contains four A7 gray-arsenic-type layers of antimony alternating with Sb(2)Te(3) slabs. Joint refinements on single-crystal diffraction data using synchrotron radiation at several K edges were performed to enhance the scattering contrast. These refinements show that the elemental distributions at some atom positions are disordered whereas otherwise the structures are long-range ordered. The variation of the elemental concentration correlates with the variation in interatomic distance. Z-contrast scanning transmission electron microscopy (HAADF-STEM) on 39R-Ge(0.067)Sb(0.667)Te(0.266) confirms the presence of concentration gradients. The carrier-type of the isostructural metal (A7-type lamellae)-semiconductor heterostructures (Ge/Sn-doped Sb(2)Te(3) slabs) varies from n-type (Ge(0.067)Sb(0.667)Te(0.266)) to p-type (Sn(0.067)Sb(0.667)Te(0.266)). Although the absolute values of the Seebeck coefficient reached about 50-70 μV/K and the electrical conductivity is relatively high, the two isotypic phases exhibit a maximal thermoelectric figure of merit (ZT) of 0.06 at 400 °C as their thermal conductivity (κ≈8-9.5 W/mK at 400 °C) lies interestingly in between that of antimony and pure Sb(2)Te(3). 相似文献