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排序方式: 共有384条查询结果,搜索用时 187 毫秒
1.
On alkalinization of solutions of the chromiun(III)-aquo ion simple deprotonation takes place first. The degree of hydroxylation n OH however can be brought up to only about 1 (the exact value depending on the total concentration [Cr]t), before the uncharged complex Cr(OH)3(OH2)3 is precipitated. The structure of the very sparingly soluble complex (solubility ~10?7M ) is held together by hydrogen bonds of type I between the molecules, so that its formula may be written as Cr(OH)2H6/2-lattice. The formation of the well ordered structure is extremely fast. On aging, the metallic centers become connected by μ-hydroxo-bridges (type II) and the substances become amorphous and very insoluble. The dinuclear (H2O)4Cr(OH)2Cr(OH2)44+ behaves similar on deprotonation. Concerning the various equilibria constants see Table 1. 相似文献
2.
Nielsen UG Topsøe NY Brorson M Skibsted J Jakobsen HJ 《Journal of the American Chemical Society》2004,126(15):4926-4933
The first observations of the complete manifold of spinning sidebands (ssbs) including both the central and satellite transitions in (51)V MAS NMR spectra of surface vanadia nanoparticles on titania in DeNO(x) catalysts are presented. (51)V quadrupole coupling and chemical shift anisotropy parameters for the dominating vanadia structure are determined from (51)V MAS NMR spectra recorded at 9.4 and 14.1 T. Based on correlations previously established between (51)V NMR parameters and crystal structure data for inorganic vanadates, the NMR data are consistent with vanadium in a distorted octahedral oxygen coordination environment for the so-called strongly bonded vanadia species on the surface. The investigation includes two vanadia-titania model catalysts and six industrial-type DeNO(x) catalysts. 相似文献
3.
David Bevk Uroš Grošelj Anton Meden Jurij Svete Branko Stanovnik 《Helvetica chimica acta》2007,90(9):1737-1744
A simple and efficient synthesis of four new substituted pyrimidines, compounds 9a – d , from the title compound 3 is described. Conversion of 3 to methyl (E)‐3‐(dimethylamino)‐2‐(6‐methoxy‐2‐phenylpyrimidin‐4‐yl)prop‐2‐enoate ( 4 ), followed by condensation with various dinucleophiles according to the ‘enaminone methodology’, afforded the target compounds 9 in medium‐to‐good yields. 相似文献
4.
Th. Rubehn W. F. J. Müller R. Bassini M. Begemann-Blaich Th. Blaich A. Ferrero C. Groß G. Imme I. Iori G. J. Kunde W. D. Kunze V. Lindenstruth U. Lynen T. Möhlenkamp L. G. Moretto B. Ocker J. Pochodzalla G. Raciti S. Reito H. Sann A. Schüttauf W. Seidel V. Serfling W. Trautmann A. Trzcinski G. Verde A. Wörner E. Zude B. Zwieglinski 《Zeitschrift für Physik A Hadrons and Nuclei》1995,353(2):197-204
Electromagnetic fission of238U projectiles at E/A =600 and 1000 MeV was studied with the ALADIN spectrometer at the heavy-ion synchrotron SIS. Seven different targets (Be, C, Al, Cu, In, Au and U) were used. By considering only those fission events where the two charges added up to 92, most of the nuclear interactions were excluded. The nuclear contributions to the measured fission cross sections were determined by extrapolating from beryllium to the heavier targets with the concept of factorization. The obtained cross sections for electromagnetic fission are well reproduced by extended Weizsäcker-Williams calculations which include E1 and E2 excitations. The asymmetry of the fission fragments' charge distribution gives evidence for the excitation of the double giant-dipole resonance in uranium.Communicated by V. Metag 相似文献
5.
A. Weidinger J. Erxmeyer H. Glückler Ch. Niedermayer O. Laforsch J. Groß M. Mehring 《Hyperfine Interactions》1994,86(1):609-614
Hydrogenated YBa2Cu3O7 with [H]/cell=2.0 was studied by X-ray diffraction, SR and1H-NMR. For the first time, the hydride phase (16% larger c-axis) known from thin film experiments was seen in a bulk sample. A comparison of the SR and NMR results shows that the 15 mT site (2 MHz in SR) is the stable position for the proton and muon. The three other muon sites (4 MHz line and two exponentially decaying components) are metastable. 相似文献
6.
U. Groß P. Dietrich G. Engler D. Prescher J. Schulze K. Lunkwitz A. Ferse 《Journal of fluorine chemistry》1982,20(1):33-52
The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N2, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides. 相似文献
7.
8.
The 1O2-induced degradation of spiro[1,8a]dihydroindolizines - a new photochromic system - may involve dioxetanes as intermediates giving fulvenylesters . 相似文献
9.
Magnetically disordered, strong correlated itinerant electron systems are studied within the Hubbard model. Following an alloy analogy, the approximated system hamiltonian contains local vectoral magnetic fields at the atomic sites, which can be oriented into all space directions. The statistical system of the localized magnetic moments (due to the fields) is treated by the aid of a generalized CPA-technique. Supposing a macroscopic magnetic structure of sublattice antiferromagnetism, the formation of incomplete antiferromagnetic ordering of the localized moments is examined. The results show, that the electron density plays an essential roll for the question, whether or not it is possible to go beyond the pure (itinerant) antiferromagnetic state. Including the results of earlier papers for homogeneous macroscopic magnetic structure, on the whole scale of electron densities it is summed up (at zero temperature), where the different states (without-, with incomplete- or with complete magnetic order) are able to exist. It is shown, for fixed density respectively, which different phases are passed through on changing the coupling constant.Work supported by the Deutsche Forschungsgemeinschaft 相似文献
10.
Dr.-Ing. K. P. Großkurth 《Colloid and polymer science》1981,259(2):163-170
Zusammenfassung Im vorfibrillaren Stadium besitzt die Crazematerie eine in Verformungsrichtung deformierte Netzwerkstruktur, die sich bei Polystyrol und Styrol-Acrylnitril-Copolymerisat elektronenoptisch an Oberflächenabdrücken sauerstoffionengeätzter Proben nachweisen läßt. Während die durchschnittlichen Globulitverformungen zumeist deutlich unterhalb von 50% liegen, werden partiell Spitzenwerte von bis zu 300% erreicht. Am Beispiel des Polystyrols verdeutlichen quantitative Strukturvergleiche mit warmgerecktem Material, daß die molekulare Beweglichkeit während des Crazewachstums und der Schulter-Hals-Verstreckung derjenigen entspricht, die für thermisch aktiviertes Material oberhalb der Glastemperatur charakteristisch ist.Mit 7 Abbildungen und 2 Tabellen 相似文献