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排序方式: 共有442条查询结果,搜索用时 15 毫秒
1.
Van Nhu Nguyen Robert Deja Roland Peters Ludger Blum Detlef Stolten 《International Journal of Hydrogen Energy》2018,43(36):17520-17530
This paper presents an experimental study of catalytic hydrogen combustion that used commercial catalysts containing Pt in a honeycomb monolith reactor in a plug flow configuration. The emphasis is on determining global kinetics in the case of low hydrogen content. Measurements of the temperature and composition of the reaction product at the outlet in the steady state condition at the different initial compositions of hydrogen and total volumetric feed rates were performed. The conversion of hydrogen was determined in parallel to the composition of the reaction product at the outlet using GC as well as by means of the thermodynamic approach using material and energy balances. The influence of the flow rate and initial molar fraction of hydrogen on hydrogen conversion is shown. A kinetic expression of the Arrhenius type is proposed with the reaction first order in hydrogen and zero order in oxygen for the overall process of the oxidation of hydrogen in lean hydrogen-air mixtures. The determined activation energy was in good agreement with the desorption activation energy for O2 from graphene-covered Pt(111) surfaces using temperature-programmed desorption. This result shows transport-limitations for heterogeneous hydrogen conversion in catalytic hydrogen combustion. 相似文献
2.
Chemikalienfreie Bekämpfung von Holzschädlingen durch dielektrische Erwärmung mit Radiowellen und Mikrowellen 下载免费PDF全文
Christian Hoyer Christian Pfütze Dr. Rudy Plarre Dr. Ulf Trommler Steffen Steinbach Kerstin Klutzny Dr. Frank Holzer Carsten Rabe Björn Höhlig Prof. Frank‐Dieter Kopinke Prof. Detlef Schmidt Dr. Ulf Roland 《化学,工程师,技术》2014,86(8):1187-1197
Thermal pest control requires long treatment times due to the low thermal conductivity of wood and may lead to the formation of cracks. Here, the thermal treatment with radio waves as well as microwaves has been studied. The direct dielectric heating has the advantage of a good homogeneity. The obtained temperature profiles for radio waves were more homogeneous compared to microwaves. Detailed studies showed that elimination of pests was not related to the application of the electromagnetic field itself, but due to the temperature increase. 相似文献
3.
The effective removal of emerging contaminants of concern (ECCs) such as endocrine-disrupting chemicals, pharmaceutically active compounds, personal care products, and flame retardants is a desirable water treatment goal. In this study, one activated carbon, one carbonaceous resin, and two high-silica zeolites were studied to evaluate their effectiveness for the removal of an ECC mixture from lake water. Adsorption isotherm experiments were performed with a mixture of 28 ECCs at environmentally relevant concentrations (200–900 ng/L). Among the tested adsorbents, activated carbon was the most effective, and activated carbon doses typically used for taste and odor control in drinking water (<10 mg/L) were sufficient to achieve a 2-log removal for most of the tested ECCs. The carbonaceous resin was less effective than the activated carbon because this adsorbent had a smaller volume of pores in the size range required for the adsorption of many ECCs (6–9 Å). For the removal of ECC mixture constituents, zeolites were less effective than the carbonaceous adsorbents. Because zeolites contain pores of uniform size and shape, a few of the tested ECCs with matching pore size/shape requirements were well removed, but the adsorptive removal of others was negligible, even at zeolite doses of 100 mg/L. The results of this study demonstrate that effective adsorbents for the removal of a broad spectrum of ECCs from water should exhibit heterogeneity in pore size and shape and a large pore volume in the 6–9 Å size range. 相似文献
4.
Widely Tunable Morphologies in Block Copolymer Thin Films Through Solvent Vapor Annealing Using Mixtures of Selective Solvents 下载免费PDF全文
Michelle A. Chavis Detlef‐M. Smilgies Ulrich B. Wiesner Christopher K. Ober 《Advanced functional materials》2015,25(20):3057-3065
Thin films of block copolymers are extremely attractive for nanofabrication because of their ability to form uniform and periodic nanoscale structures by microphase separation. One shortcoming of this approach is that to date the design of a desired equilibrium structure requires synthesis of a block copolymer de novo within the corresponding volume ratio of the blocks. In this work, solvent vapor annealing in supported thin films of poly(2‐hydroxyethyl methacrylate)‐block‐poly(methyl methacrylate) [PHEMA‐b‐PMMA] by means of grazing incidence small angle X‐ray scattering (GISAXS) is investigated. A spin‐coated thin film of a lamellar block copolymer is solvent vapor annealed to induce microphase separation and improve the long‐range order of the self‐assembled pattern. Annealing in a mixture of solvent vapors using a controlled volume ratio of solvents, which are chosen to be preferential for each block, enables selective formation of ordered lamellae, gyroid, hexagonal, or spherical morphologies from a single‐block copolymer with a fixed volume fraction. The selected microstructure is then kinetically trapped in the dry film by rapid drying. This paper describes what is thought to be the first reported case where in situ methods are used to study the transition of block copolymer films from one initial disordered morphology to four different ordered morphologies, covering much of the theoretical diblock copolymer phase diagram. 相似文献
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6.
Detlef Hühnlein 《Datenschutz und Datensicherheit - DuD》2014,38(4):217-217
7.
Verena Preis Sebastian Hahnel Carola Kolbeck Detlef Behrend Mareike Warkentin Gerhard Handel Martin Rosentritt 《Advanced Engineering Materials》2011,13(12):B432-B439
The aim of this in vitro study was to compare the two‐body wear resistance of different dental ceramics and non‐precious alloys. Two‐body wear tests were performed in a chewing simulator with steatite antagonists. A pin‐on‐block design with a vertical load of 50 N for 1.2 × 105 cycles (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. Surface roughness Ra (SP6, Perthen‐Feinprüf, G) and wear depth were determined using a 3D‐Profilometer (Laserscan 3D, Willytec, G). Scanning electron microscopy (Quanta FEG 400, FEI, NL) was applied for evaluating wear performance of both, materials and antagonists. Statistics: one‐way ANOVA (α = 0.05). The in vitro wear test showed that the wear performance of dental materials is strongly influenced by the type of material (ceramic, zirconia, or alloy). Zirconia and alloy provided low wear in contrast to glass‐ceramic systems. In contradiction to common expectations, hard zirconia and alloy systems showed even lower antagonistic wear than glass‐ceramics. 相似文献
8.
Large‐scale Synthesis of Urchin‐like Mesoporous TiO2 Hollow Spheres by Targeted Etching and Their Photoelectrochemical Properties 下载免费PDF全文
Jia Hong Pan Xing Zhu Wang Qizhao Huang Chao Shen Zhen Yu Koh Qing Wang Astrid Engel Detlef W. Bahnemann 《Advanced functional materials》2014,24(1):95-104
A versatile targeted etching strategy is developed for the large‐scale synthesis of urchin‐like mesoporous TiO2 hollow spheres (UMTHS) with tunable particle size. Its key feature is the use of a low‐temperature hydrothermal reaction of surface‐fluorinated, amorphous, hydrous TiO2 solid spheres (AHTSS) under the protection of a polyvinylpyrrolidone (PVP) coating. With the confinement of PVP and water penetration, the highly porous AHTSS are selectively etched and hollowed by fluoride without destroying their spherical morphology. Meanwhile TiO2 hydrates are gradually crystallized and their growth is preferentially along anatase (101) planes, reconstructing an urchin‐like shell consisting of numerous radially arranged single‐crystal anatase nanothorns. Complex hollow structures, such as core–shell and yolk–shell structures, can also be easily synthesized via additional protection of the interior by pre‐filling AHTSS with polyethylene glycol (PEG). The hollowing transformation is elucidated by the synergetic effect of etching, PVP coating, low hydrothermal reaction temperature, and the unique microstructure of AHTSS. The synthesized UMTHS with a large surface area of up to 128.6 m2 g‐1 show excellent light‐harvesting properties and present superior performances in photocatalytic removal of gaseous nitric oxide (NO) and photoelectrochemical solar energy conversion as photoanodes for dye‐sensitized mesoscopic solar cells. 相似文献
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10.
Junying Liu Rui Zhang Itaru Osaka Sarada Mishra Anna E. Javier Detlef‐M. Smilgies Tomasz Kowalewski Richard D. McCullough 《Advanced functional materials》2009,19(21):3427-3434
New solution processable 4‐(2‐hexyldecan)‐4H‐bisthieno[2,3‐d:3′,2′‐b]pyrrole and 4,4′‐dialkyl‐2,2′‐bithiazole‐based copolymers (PBTzDTPs) are synthesized with excellent FET performance. These novel copolymers have considerable potential in printable electronics as they have high charge carrier mobilities, excellent air stability, good solution processibility, and no requirement for post‐deposition thermal annealing, all requirements for this field of application. The thin film transistors fabricated from PBTzDTPs achieve field effect mobilities as high as 0.14 cm2 V?1 s?1 with current on/off ratios up to 106 without thermal annealing. In addition, the devices exhibit stable performance in air, showing no significant degradation over 60 days. Moreover, the polymers described here provide an excellent example of the systems in which higher mobility performance does not require higher crystalline, long‐range ordered structures. Such a system appears to be particularly promising for rapid fabrication techniques, where kinetic conditions usually prevent the development of long‐range order. 相似文献