Neutron diffraction study of yttrium α'-sialon

The structure of yttrium a'-Sialon ceramic of compn. Y0.5Si9.75Al2.25N15.25O0.75 was examd. by powd. neutron diffraction and Rietfeld refinement of the data. [on SciFinder (R)

Flooding of Regular Phase Space Islands by Chaotic States

We investigate systems with a mixed phase space, where regular and chaotic dynamics coexist. Classically, regions with regular motion, the regular islands, are dynamically not connected to regions with chaotic motion, the chaotic sea. Typically, this is also reflected in the quantum properties, where eigenstates either concentrate on the regular or the chaotic regions. However, it was shown that quantum mechanically, due to the tunneling process, a coupling is induced and flooding of regular islands may occur. This happens when the Heisenberg time, the time needed to resolve the discrete spectrum, is larger than the tunneling time from the regular region to the chaotic sea. In this case the regular eigenstates disappear. We study this effect by the time evolution of wave packets initially started in the chaotic sea and find increasing probability in the regular island. Using random matrix models a quantitative prediction is derived. We find excellent agreement with numerical data obtained for quantum maps and billiards systems. For open systems we investigate the phenomenon of flooding and disappearance of regular states, where the escape time occurs as an additional time scale. We discuss the reappearance of regular states in the case of strongly opened systems. This is demonstrated numerically for quantum maps and experimentally for a mushroom shaped microwave resonator. The reappearance of regular states is explained qualitatively by a matrix model.Untersucht werden Systeme mit gemischtem Phasenraum, in denen sowohl reguläre als auch chaotische Dynamik auftritt. In der klassischen Mechanik sind Gebiete regulärer Bewegung, die sogenannten regulären Inseln, dynamisch nicht mit den Gebieten chaotischer Bewegung, der chaotischen See, verbunden. Dieses Verhalten spiegelt sich typischerweise auch in den quantenmechanischen Eigenschaften wider, so dass Eigenfunktionen entweder auf chaotischen oder regulären Gebieten konzentriert sind. Es wurde jedoch gezeigt, dass aufgrund des Tunneleffektes eine Kopplung auftritt und reguläre Inseln geflutet werden können. Dies geschieht wenn die Heisenbergzeit, das heißt die Zeit die das System benötigt, um das diskrete Spektrum aufzulösen, größer als die Tunnelzeit vom Regulären ins Chaotische ist, wobei reguläre Eigenzustände verschwinden. Dieser Effekt wird über eine Zeitentwicklung von Wellenpaketen, die in der chaotischen See gestartet werden, untersucht. Es kommt zu einer ansteigenden Wahrscheinlichkeit in der regulären Insel. Mithilfe von Zufallsmatrixmodellen wird eine quantitative Vorhersage abgeleitet, welche die numerischen Daten von Quantenabbildungen und Billardsystemen hervorragend beschreibt. Der Effekt des Flutens und das Verschwinden regulärer Zustände wird ebenfalls mit offenen Systemen untersucht. Hier tritt die Fluchtzeit als zusätzliche Zeitskala auf. Das Wiederkehren regulärer Zustände im Falle stark geöffneter Systeme wird qualitativ mithilfe eines Matrixmodells erklärt und numerisch für Quantenabbildungen sowie experimentell für einen pilzförmigen Mikrowellenresonator belegt

Plasma-enhanced atomic layer deposition of titania of alumina for its potential use as a hydrogen-selective membrane

As a clean energy carrier, hydrogen has attracted global attention in recent years, because it could address issues that are related to reducing global climate change. It has to be stipulated that to date's processes for hydrogen production using fossil fuels need to be coupled with CO2 separation and storage. Thermally and hydrothermally stable microporous membranes with intrinsic high H2/CO2 selectivity are highly demanded in steam-reforming and water gas-shift processes for H2 gas separation. In this study a composite alumina–titania membrane was synthesized by the combination of atomic layer deposition (ALD) and sol–gel processes. By adjusting the number of ALD cycles (280 cycles), a thin TiO2 layer corresponding to a thickness of ~10 nm was deposited on the surface of ¿-Al2O3 membranes. The gas permeation was tested to assess the membranes’ gas separation performance. The membranes exhibited a good balance between H2 permeance and separation properties. At 450 K, the H2 permeance is approximately 12.5 × 10-8 mol m-2 s-1 Pa-1 and the separation factor is 5.8 for a H2/CO2 mixture. The results clearly demonstrate that the studied deposition method ALD is a promising route to prepare ceramic microporous membranes for hydrogen separation

Approximation of theoretical energy-saving potentials for the petrochemical industry using energy balances for 68 key processes

We prepared energy and carbon balances for 68 petrochemical processes in the petrochemical industry for Western Europe, the Netherlands and the world. We analysed the process energy use in relation to the heat effects of the chemical reactions and quantified in this way the sum of all energy inputs into the processes that do not end up in the useful products of the process, but are lost as waste heat to the environment. We showed that both process energy use and heat effects of reaction contribute significantly to the overall energy loss of the processes studied and recommend addressing reaction effects explicitly in energy-efficiency studies. We estimated the energy loss in Western Europe in the year 2000 at 1620 PJ of final energy and 1936 PJ of primary energy, resulting in a total of 127 Mt CO2. The losses identified can be regarded as good approximations of the theoretical energy-saving potentials of the processes analysed. The processes with large energy losses in relative (per tonne of product) and absolute (in PJ per year) terms are recommended for more detailed analysis taking into account further thermodynamic, economic, and practical considerations to identify technical and economic energy-saving potentials

Economic perspectives of Power-to-Gas technologies in bio-methane production

A study on integration of Power-to-Gas technology with bio-methane production from bio-syngas produced by biomass gasification shows that a significant amount of excess electricity can be accommodated in bio-SNG production. By adding hydrogen produced from intermittent renewable sources to a CO2 methanation section, production capacity of methane can be doubled. The business case for Power-to-Gas for bio-methane has been evaluated using three future cumulative electricity prices curves. Results show that a positive business case exists only for price curves based on large amounts of intermittent electricity installed. The room for investment for the electrolyser will mainly and highly depend on future commodity prices and price curves, and will benefit significantly from a decrease in the cost price of the electrolyser. The projected room for investment available for a PEM electrolyser is lower than for a Solid Oxide Electrolyzer (SOE), because of its lower efficiency and resulting higher operating costs. In the case of large capacity of intermittent electricity, the projected room for investment of an SOE electrolyser is 650 €/kW and for a PEM electrolyser 350 €/kW, which corresponds to the projections of future electrolyser costs.Accepted Author ManuscriptLarge Scale Energy Storag