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排序方式: 共有557条查询结果,搜索用时 15 毫秒
111.
Stephan Stich Kuan Ding Qaisar Khushi Muhammad Lukas Porz Christian Minnert Wolfgang Rheinheimer Karsten Durst Jürgen Rödel Till Frömling Xufei Fang 《Journal of the American Ceramic Society》2022,105(2):1318-1329
Dislocations have been identified to modify both the functional and mechanical properties of some ceramic materials. Succinct control of dislocation-based plasticity in ceramics will also demand knowledge about dislocation interaction with point defects. Here, we propose an experimental approach to modulate the dislocation-based plasticity in single-crystal SrTiO3 based on the concept of defect chemistry engineering, for example, by increasing the oxygen vacancy concentration via reduction treatment. With nanoindentation and bulk compression tests, we find that the dislocation-governed plasticity is significantly modified at the nano-/microscale, compared to the bulk scale. The increase in oxygen vacancy concentration after reduction treatment was assessed by impedance spectroscopy and is found to favor dislocation nucleation but impede dislocation motion as rationalized by the nanoindentation pop-in and nanoindentation creep tests. 相似文献
112.
113.
Holger Rueß Jonas Werner Yeliz Unutulmazsoy Jürgen W. Gerlach Xiang Chen Bastian Stelzer Denis Music Szilard Kolozsvari Peter Polcik Thomas E. Weirich Jochen M. Schneider 《Journal of the European Ceramic Society》2021,41(3):1841-1847
The applicability of Cr2AlC MAX-phases as protective coatings in energy conversion or aerospace applications requires a dense, single-phase structure. Therefore, we study the effect of target power density and substrate bias on phase formation, microstructure evolution, and mechanical properties of Cr2AlC coatings utilizing direct current (DCMS) and high-power pulsed magnetron sputtering (HPPMS). Generally, HPPMS results in coatings with superior density and hence larger elastic moduli compared to DCMS, indicating that ion bombardment by ionized film-forming species is beneficial. However, decreasing the substrate bias to ?200 V for DCMS and ?100 V for HPPMS favors the ion bombardment induced formation of the disordered (Cr,Al)2Cx solid solution. It is evident that there is an optimum moderate ion energy for the formation of dense Cr2AlC coatings. Too low energy results in the formation of under-dense coatings. Too high energy yields the formation of (Cr,Al)2Cx in addition to Cr2AlC. 相似文献
114.
An-Phuc Hoang Sebastian Steiner Fan Yang Linhao Li Derek C. Sinclair Till Frömling 《Journal of the European Ceramic Society》2021,41(4):2587-2595
The demand for capacitors exhibiting low sensitivity towards temperature changes and high power peaks has increased significantly. Recently, Na0.5Bi0.5TiO3 (NBT) based ceramics became excellent candidates for such extreme temperature capacitors. The dielectric loss of these materials is, however, difficult to control because of the complex defect chemistry of NBT based ceramics. Therefore, it is the limiting factor for high temperature applications. In this work, we present a strategy to increase the upper temperature limit for low dielectric loss. The addition of BiAlO3 to Na0.5Bi0.5TiO3-BaTiO3-CaZrO3 reduces the loss and sensitivity towards Bi evaporation during synthesis. For unmodified samples, the relative permittivity (εr = 581, at 1 kHz) varies less than 15 %, while the dielectric loss stays below 0.02 between -68 and 368 °C. With the addition of BiAlO3, the temperature range of low loss extends from -68 to 391 °C at even higher permittivity (εr = 628, at 1 kHz). 相似文献
115.
During our ongoing project on the biosynthesis of R-(+)-octane-1,3-diol the metabolism of linoleic acid was investigated in stored apples after injection of [1-14C]-, [9,10,12,13-3H]-, 13C18- and unlabeled substrates. After different incubation periods the products were analyzed by gas chromatography-mass spectroscopy
(MS), high-performance liquid chromatography-MS/MS, and HPLC-radiodetection. Water-soluble compounds and CO2 were the major products whereas 13(R)-hydroxy- and 13-keto-9(Z),11(E)-octadecadienoic acid, 9(S)-hydroxy-and 9-keto-10(E),12(Z)-octadecadienoic acid, and the stereoisomers of the 9,10,13- and 9,12,13-trihydroxyoctadecenoic acids were identified as
the major metabolites found in the diethyl ether extracts. Hydroperoxides were not detected. The ratio of 9/13-hydroxy- and
9/13-keto-octadecadienoic acid was 1∶4 and 1∶10, respectively. Chiral phase HPLC of the methyl ester derivatives showed enantiomeric
excesses of 75% (R) and 65% (S) for 13-hydroxy-9(Z),11(E)-octadecadienoic acid and 9-hydroxy-10(E),12(Z)-octadecadienoic acid, respectively. Enzymatically active homogenates from apples were able to convert unlabeled linoleic
acid into the metabolites. Radiotracer experiments showed that the transformation products of linoleic acid were converted
into (R)-octane-1,3-diol. 13(R)-Hydroxy-9(Z), 11(E)-octadecadienoic acid is probably formed in stored apples from 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid. It is possible that the S-enantiomer of the hydroperoxide is primarily degraded by enzymatic side reactions, resulting in an enrichment of the R-enantiomer and thus leading to the formation of 13(R)-hydroxy-9(Z),11(E)-octadecadienoic acid. 相似文献
116.
Reduction of nitrogen dioxide by propene over acidic mordenites: influence of acid site concentration, formation of by-products and mechanism 总被引:2,自引:0,他引:2
Till Gerlach Uta Illgen Michael Bartoszek Manfred Baerns 《Applied catalysis. B, Environmental》1999,22(4):434-278
The reduction of nitrogen dioxide to nitrogen by propene was studied over a variety of acidic mordenite zeolites differing in their Si : Al ratio and thus, in their concentration of acid sites. The formation of by-products was monitored applying an ion–molecule reaction (IMR) mass spectrometer. It was found that at fixed conditions the yield of nitrogen increases with increasing concentration of acid sites, confirming that acid sites are the active catalytic centres in the reaction. Apart from nitrogen and nitric oxide, acrylonitrile and ammonia are formed as nitrogen containing gas-phase products in the reaction. In separate experiments, it was shown that acrylonitrile is hydrolysed by water over the acidic zeolites to yield ammonia and acrylic acid. When acrylonitrile is used as reducing agent for nitrogen dioxide, formation of nitrogen is strongly enhanced in the presence of water. Water also has a promoting effect on the formation of nitrogen in the reaction between nitrogen dioxide and propene. Acrylonitrile and its product of hydrolysis, ammonia, are considered to be intermediates of nitrogen dioxide reduction to nitrogen by propene over acidic zeolites. 相似文献
117.
G. Suchaneck R. Labitzke B. Adolphi L. Jastrabik P. Adamek J. Drahokoupil Z. Hubicka D.A. Kiselev A.L. Kholkin G. Gerlach A. Dejneka 《Surface & coatings technology》2011
In this work, Pb(Zr,Ti)O3 (PZT) thin films were deposited onto flexible Cu-coated Kapton® substrates by means of reactive magnetron sputtering for the first time. Different power supplies were selected for each of the 200 mm targets to adjust film composition and substrate ion bombardment. High-power pulse sputtering has been employed for the Zr-target to enhance for formation of nanocrystals, pulsed DC sputtering for the Ti-target to provide a high enough sputter yield, and RF-sputtering for the Pb-target to prevent droplet formation. The deposited films had a lead-enriched layer at the surface and their film composition was in rhombohedral range near the morphotropic phase boundary of the PZT phase diagram. XRD revealed a nanocrystallite mixture of lead, zirconium and titanium oxides in the as-deposited films which can be transferred into perovskite Pb(Zr,Ti)O3 by rapid temperature annealing. Observed piezoelectric properties demonstrate that rapid-temperature-annealed films are promising for application in flexible piezoelectric sensors, actuators and power generators. 相似文献
118.
A direct electrochemical refrigeration cycle (DERC) uses the entropy change of an electrochemical reaction to produce cooling. The cycle is Carnot limited. The electricity recycled in the DERC is much larger than the energy input to the system. Therefore, the system is sensitive to small inefficiencies in the internal energy cycling. In addition, a DERC is modelled assuming that the electrochemical cells have a constant internal resistance. By modelling the electrodes as parallel plates, an optimal channel size on the order of tens of microns can be computed depending on the electrical resistivity and viscosity of the electrolyte. The maximum cooling flux is on the order of 1000 W m−2. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
119.
G. Sand J. Till T. Tometzki M. Urselmann S. Engell M. Emmerich 《Computers & Chemical Engineering》2008,32(11):2706-2722
An engineered evolutionary algorithm for a realistic chemical batch scheduling problem with uncertain data is developed systematically. The problem is formulated as a two stage stochastic integer program with discrete scenarios. The model is solved by a stage decomposition-based hybrid algorithm using an evolutionary algorithm combined with mixed-integer programming. Earlier experiments with a standard evolutionary algorithm led to the hypothesis that the constrained search space is not covered well such that in some cases the population converges to a subset of the solution space which does not include the best known solution. An efficient engineered evolutionary algorithm is developed which is shown to cover the feasible set significantly better such that a high quality feasible schedule can be generated comparatively fast. As the hierarchical structure of the case study is typical for many batch scheduling problems, some general principles may be postulated from the experience gained here. 相似文献
120.