1,721,298 research outputs found
Neue Strategie für mechanistische Studien zu Prozessen der Chemischen Gasphasenabscheidung (CVD) unter Ultrahochvakuum (UHV)
No full textThis PhD thesis aimed at contributing to the mechanistic understanding of the growth conditions of metallic films synthesized by the previously established technique of pulsed spray evaporation chemical vapor deposition (PSE-CVD). Nickel and cobalt were selected as an example to study links between the macroscopic deposition conditions and the microscopic processes involving the precursor, surface properties and the growing thin film. The present work addressed important features of the growth process including the influence of various CVD parameters on the growth kinetics, such as the nature of the metal centre, the temperature sensitivity of carbon contamination, the function of ethanol, both as a solvent as well as a catalytic agent, influence of nickel as a seed layer for different combinations of boundary conditions, the role of water on CVD of Ni and Co thin films from ethanol solutions. Furthermore, investigation of the mechanisms of PSE-CVD from acetylacetonate metal precursors in ethanol, as well as thermal and electron beam-induced decomposition of solvent-free layers of intact Co(acac)2 and Ni(acac)2 was performed
Kinetics in the real world: linking molecules, processes, and systems
No full textKohse-Höinghaus K, Troe J, Grabow J-U, Olzmann M, Friedrichs G, Hungenberg K-D. Kinetics in the real world: linking molecules, processes, and systems. Physical Chemistry Chemical Physics. 2018;20(16):10561-10568
Modellbasierte Regelung hochdynamischer Verbrennungsvorgänge
No full textThis work originates from the Collaborative Research Center 686 "Model-based Control of Homogenized Low-Temperature Combustion". It describes the development of a model-based predictive control concept to stabilize highly-dynamic combustion processes. The design of this concept consists of three main phases: Model development, design of the actual control algorithm and an implementation capable of real-time execution.The model development in this work is based on chemical reaction mechanisms, consisting of up to several hundred elementary reactions. The chemical reaction rates calculated using these mechanisms are then applied in mass and energy balancing equations resulting in a nonlinear state-space model.This model is then applied in different linear and nonlinear predictive schemes to stabilize combustion processes in numerical simulations at a desired operating point. Based on the simulation results, a linear scheme was selected for the application on the real system.The implementation involved the development of a fast and slim chemical-kinetic engine as well as the implementation of a variable step size solver for differential equations within the real-time framework of the control system.After implementing the control concept in a real-time capable manner, it was successfully applied on a stirred-reactor test bench, supplied by the Institute of Technical Combustion (ITV) at RWTH Aachen University
The role of homogeneous gas-phase reactions in emission control of combustion engines and reforming of steel mill off-gases
No full textFourier transform microwave spectroscopic studies of dimethyl ether and ethylene flames
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Previous issue date: 6Microwave spectroscopy has been a proven technique for the detection of short-lived molecules produced from a variety of molecular sources. With the goal of observing more reactive intermediates produced in combustion reactions, the products of a home-built flat flame burner were measured on a coaxially oriented beam resonator arrangement (COBRA) Fourier transform microwave spectrometer.footnote{J.-U. Grabow, W. Stahl, H. Dreizler, Rev. Sci. Instrum. 67, 4072, 1996} The products are coupled into a molecular beam using a fast-mixing nozzle styled after the work of Gutowsky and co-workers.footnote{T. Emilsson, T. D. Klots, R. S. Ruoff, H.S. Gutowsky, J. Chem. Phys. 93, 6971, 1990}_x000d_
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Probing the flame at various positions, the relative abundance of products can be observed as a function of flame depth. One dimensional intensity profiles are available for formaldehyde, ketene, acetaldehyde, and dimethyl ether, where either a dimethyl ether fuel or an ethylene fuel was burned in the presence of oxygen. The current arrangement allows only for stable species produced in the flame to be observed in the molecular beam. This combination of species source and detection shows promise for future work in observing new, short-lived, combustion intermediates._x000d_
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Phosphane and Phosphite Silver(I) Complexes: Synthesis, Reaction Chemistry and their Use as CVD Precursors
No full textSilver(I) complexes of type LnAgX (X = organic ligand, such as carboxylates, dicarboxylates, Schiff-base; L = Lewis-bases, e. g. PnBu3, P(OMe)3, P(OEt)3; n = 1, 2, 3) have been synthesized and characterized with respect to their suitability for the Chemical Vapour Deposition (CVD) of silver thin films. For some of these compounds single crystal could be obtained. Their solid-state structure was determined by single crystal X-ray diffraction. The volatility, thermal stability, and gas phase decomposition mechanism of selected compounds were studied using temperature-programmed and in-situ mass spectrometry. CVD experiments were performed according to the results of the gas phase analysis. Silver films could be grown by using a cold-wall CVD reactor. The morphology of the latter films was determined.Silber(I) Komplexe LnAgX (X = organische Ligand, Z. B. Carboxylate, Dicarboxylate, Schiff Base; L = Lewis-Base, Z. B. PnBu3, P(OMe)3, P(OEt)3; n = 1, 2, 3) wurden Bezug auf ihre Eignung für die chemische Gasphasenabscheidung von Silberfilmen synthetisiert und charakterisiert. Von einigen dieser Verbindung konnten Einkristalle erhalten werden. Der Bau dieser Verbindungen wurde mittels Röntgeneinkristallographie ermittelt. Ausgewählten Verbindungen wurden mit Temperatur-programmierter und in-situ Massenspektrometrie analysiert. Gasphasenabscheidungs- mechanismen für einige Prekursoren sind vorgestellt. CVD-Abscheidungsexperimente wurden entsprechend den Ergebnissen der Gasphaseanalyse durchgeführt. Silber Schichten konnten mit einen Kaltwand CVD-Reaktor erzeugt werden, deren Oberflächenmorphologie wurde untersucht
A new era for combustion research
No full textKohse-Höinghaus K. A new era for combustion research. Pure and Applied Chemistry. 2019;91(2):271-288.Current topics in combustion chemistry include aspects of a changing fuel spectrum with a focus on reducing emissions and increasing efficiency. This article is intended to provide an overview of selected recent work in combustion chemistry, especially addressing reaction pathways from fuel decomposition to emissions. The role of the molecular fuel structure will be emphasized for the formation of certain regulated and unregulated species from individual fuels and their mixtures, exemplarily including fuel compounds such as alkanes, alkenes, ethers, alcohols, ketones, esters, and furan derivatives. Depending on the combustion conditions, different temperature regimes are important and can lead to different reaction classes. Laboratory reactors and flames are prime sources and targets from which such detailed chemical information can be obtained and verified with a number of advanced diagnostic techniques, often supported by theoretical work and simulation with combustion models developed to transfer relevant details of chemical mechanisms into practical applications. Regarding the need for cleaner combustion processes, some related background and perspectives will be provided regarding the context for future chemistry research in combustion energy science
Diamantfilme und Rußpartikel: Reaktionswege in brennstoffreichen Flammen
No full textKohse-Höinghaus K. Diamantfilme und Rußpartikel: Reaktionswege in brennstoffreichen Flammen. Chemie in unserer Zeit. 1998;32(5):242-250
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