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111.
112.
Stage-I fatigue cracks are commonly described by the model of Bilby, Cottrell and Swinden (BCS model). However, since several experimental investigations have shown a dislocation-free zone (DFZ) in front of crack-tips, it is necessary to validate the new DFZ model and to examine the deviations to the BCS model. Therefore, the dislocation density distribution is derived from height profiles of slip lines in front of stage-I fatigue cracks in CMSX4® single crystals measured by contact-mode atomic force microscopy. This is possible, because the cracks are initiated at notches milled by focused ion beam technique directly on slip planes with a high Schmid factor. Consequently, the directions of the Burgers vectors are well known; it is possible to calculate the dislocation density distributions from the height profiles. The measured distributions are compared to the calculated distribution function of the DFZ model proposed by Chang et al. The additionally measured microscopic friction stress of the dislocations is then used to calculate the influence of grain boundaries on the dislocation density distribution in front of stage-I cracks. The calculation is done by the extended DFZ model of Shiue et al. and compared with the measured distribution function in polycrystalline specimens. Finally, the crack-tip sliding displacement as a measure for the crack propagation rate is compared for the DFZ model and the BCS model with the experimentally revealed values. The important result: the often used BCS model does not reflect the experimental measurements. On the contrary, the DFZ model reflects the measurements at stage-I cracks qualitatively and quantitatively. 相似文献
113.
Alexey Marchuk Florian J. Pucher Friedrich W. Karau Prof. Dr. Wolfgang Schnick 《Angewandte Chemie (International ed. in English)》2014,53(9):2469-2472
Phosphorus nitride imide, PN(NH), is of great scientific importance because it is isosteric with silica (SiO2). Accordingly, a varied structural diversity could be expected. However, only one polymorph of PN(NH) has been reported thus far. Herein, we report on the synthesis and structural investigation of the first high‐pressure polymorph of phosphorus nitride imide, β‐PN(NH); the compound has been synthesized using the multianvil technique. By adding catalytic amounts of NH4Cl as a mineralizer, it became possible to grow single crystals of β‐PN(NH), which allowed the first complete structural elucidation of a highly condensed phosphorus nitride from single‐crystal X‐ray diffraction data. The structure was confirmed by FTIR and 31P and 1H solid‐state NMR spectroscopy. We are confident that high‐pressure/high‐temperature reactions could lead to new polymorphs of PN(NH) containing five‐fold‐ or even six‐fold‐coordinated phosphorus atoms and thus rivalling or even surpassing the structural variety of SiO2. 相似文献
114.
Platinum Complexes Containing Pyramidalized Germanium and Tin Dihalide Ligands Bound through σ,σ ME Multiple Bonds 下载免费PDF全文
Florian Hupp Dr. Mengtao Ma Franziska Kroll Dr. J. Oscar C. Jimenez‐Halla Dr. Rian D. Dewhurst Dr. Krzysztof Radacki Dr. Andreas Stasch Prof. Dr. Cameron Jones Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):16888-16898
We present the isolation of the first mononuclear dihalogermylene, and mono‐ and dinuclear stannylene complexes of transition metals. These exhibit exceptionally pyramidalized Group 14 centers. Additionally, removal of the halide substituents from the Ge/Sn atom was successfully performed in two ways, halide abstraction and reduction, leading to a variety of unusual structural motifs. 相似文献
115.
Titanium‐Catalyzed Hydroalumination of Conjugated Dienes: Access to Fulvene‐Derived Allylaluminium Reagents and Their Diastereoselective Reactions with Carbonyl Compounds 下载免费PDF全文
Dr. Jomy Joseph Dr. Florian Jaroschik Dr. Dominique Harakat Dr. K. V. Radhakrishnan Dr. Jean‐Luc Vasse Prof. Jan Szymoniak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(18):5433-5438
The described titanium‐catalyzed hydroalumination of conjugated dienes opens up a new way to allylaluminium reagents. The reaction is carried out by using diisobutylaluminium hydride (DIBAL‐H) and a catalytic amount of [Cp2TiCl2] (Cp=cyclopentadienyl). When applied to mono‐ and disubstitued pentafulvenes, this reaction proceeds in a highly endocyclic manner. The formed allylaluminium compounds react regio‐ and stereoselectively with both aldehydes and ketones to afford homoallylic alcohols that are suitable synthons for functionalized cyclopentanones. An extension of this methodology to simple dienes was also investigated. In the proposed mechanism, the initially formed bimetallic species (Ti/Al) are involved in the two possible catalytic cycles with a direct hydroalumination or/and a hydrotitanation followed by a titanium to aluminium transmetallation. 相似文献
116.
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118.
The pyrophoric compound Rb2[U(NH2)6] was obtained as a grey to black powder from the reaction of more than three equivalents of RbNH2 with UI3 in anhydrous liquid ammonia. During the process, UIII is oxidized to UIV and ammonia is reduced under evolution of H2. Rb2[U(NH2)6] crystallizes in the cubic crystal system, space group Fm3 m, with the lattice parameter a = 9.7870(12) Å, V = 937.4(2) Å3, Z = 4 at T = 293 K. It is isotypic to K2PtCl6. The compound contains the unprecedented hexaamidouranate(IV) anion [U(NH2)6]2–. 相似文献
119.
The Al45Cr7 compound is considered to exhibit an approximant structure of the icosahedral Al4Cr phase. Its (010) surface has been investigated in detail using density functional calculations. Surface energy calculations show that the stable terminations result from a cleavage of the crystal between adjacent atomic planes, in agreement with the layered structure of the compound. The integrity of the icosahedral atomic arrangements (icosahedral clusters) found in the bulk structure, is predicted to be removed at the surface. This result is in contrast to what has been previously concluded for the (010) surface of the Al13Fe4 quasicrystal approximant. Our findings are discussed in relation to the bonding network in the compound, calculated using the Crystal Orbital Hamiltonian Population approach, as possible reasons for such contrasted behavior. 相似文献
120.
Fabian Dankert H. Lars Deubner Matthias Müller Magnus R. Buchner Florian Kraus Carsten von Hänisch 《无机化学与普通化学杂志》2020,646(18):1501-1507
The work describes unexpected stoichiometric C–F bond cleavage reactions of beryllium, magnesium, gallium, hafnium and thorium halides with α,α,α-trifluorotoluene. The reaction of BeBr2 / GaBr3 or MgBr2 / GaBr3 mixtures as well as neat GaI3 with α,α,α-trifluorotoluene in the presence of (OSi2Me4)2 ( I ) yields the carbenium ion containing compounds [Ph-C(O2Si2Me4)][GaX4] (X = Br: 1 , X = I/F: 2 ). Both compounds were successfully characterized and a defluorination type reaction under incorporation of a siloxy unit was observed. Compound 1 was also characterized by single-crystal X-ray diffraction analysis. The conversion of α,α,α-trifluorotoluene with BeI2, HfI4 or ThI4 turned out to be a halodefluorination-type reaction with formation of α,α,α-triiodotoluene ( 3 ). An adequate NMR spectroscopic and the X-ray crystallographic characterization of 3 were performed for the first time. 相似文献