Phasenänderungen im System Er2O3—TiO2

Zusammenfassung Röntgenographische und Gefügeuntersuchungen werden im System Er₂O₃–TiO₂ durchgeführt und ein Phasendiagramm im Solidusbereich ermittelt. Der Homogenitätsbereich der Pyrochlor-(von 33,3 Molprozent bis 50 Molprozent Er₂O₃) und der Fluoritphase (von 50 Molprozent bis 57 Molprozent Er₂O₃) wird bei 1550°C bestimmt.

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Phase transformations in the system Er₂O₃—TiO₂

The system Er₂O₃–TiO₂ has been investigated by microscopic and X-ray procedures. A phase diagram for the solidus range has been proposed. The pyrochlore phase is homogeneous from 33.3 to 50 mole% Er₂O₃ at 1550°C. Beyond 50 and up to 57 mole% Er₂O₃, the fluorite phase is homogeneous.

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Mit 2 Abbildungen     

Two‐dimensional,unstructured mesh generation for tidal models

The successful implementation of a finite element model for computing shallow‐water flow requires the identification and spatial discretization of a surface water region. Since no robust criterion or node spacing routine exists, which incorporates physical characteristics and subsequent responses into the mesh generation process, modelers are left to rely on crude gridding criteria as well as their knowledge of particular domains and their intuition. Two separate methods to generate a finite element mesh are compared for the Gulf of Mexico. A wavelength‐based criterion and an alternative approach, which employs a localized truncation error analysis (LTEA), are presented. Both meshes have roughly the same number of nodes, although the distribution of these nodes is very different. Two‐dimensional depth‐averaged simulations of flow using a linearized form of the generalized wave continuity equation and momentum equations are performed with the LTEA‐based mesh and the wavelength‐to‐gridsize ratio mesh. All simulations are forced with a single tidal constituent, M₂. Use of the LTEA‐based procedure is shown to produce a superior (i.e., less error) two‐dimensional grid because the physics of shallow‐water flow, as represented by discrete equations, are incorporated into the mesh generation process. Copyright © 2001 John Wiley & Sons, Ltd.     

Chemical interaction and diffusion on interface cathode/electrolyte of SOFC

The high-temperature solid oxide fuel cell (SOFC) is suited for the environmentally acceptable and efficient conversion of chemical into electric energy. A prerequisite for introducing this technology on the market is the controlled formation of the interface between electrodes and the electrolyte. In the case of using an electrolyte based on LaGaO₃ the formation of third phases and the diffusion of individual metallic cations from and to the electrolyte was investigated with the aid of point analyses on micrographs of the environment of the interface using quantitative EDS analysis. In case of an anode of Ni-CeO₂ cermet the mixed oxide SrLaGa₃O₇ is formed and, in addition, a relatively pronounced transport of La from the electrolyte into the CeO₂ phase was observed. A relatively strong diffusion of Mn and an even stronger diffusion of Co into the electrolyte took place between the cathode of, e.g., La_0.75Sr_0.2Mn_0.8Co_0.2O₃ and the La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte, whereas a weak transport of Ga to the cathode was identified.     

VIENNA rectifier II-a novel single-stage high-frequency isolatedthree-phase PWM rectifier system

Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type pulsewidth modulated (PWM) rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage, which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows the realization of several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conduction states occurring within a pulse period. Furthermore, a straightforward space- vector-oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation, the theoretical considerations are verified and the stresses on the power semiconductors of the new converter system are determined. Finally, results of an experimental analysis of a 2.5-kW laboratory prototype of the system are given, and the direct startup and the short-circuit protection of the converter are discussed. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview     

Analyse eines neuen Stromrichter- und Flussregelkonzepts zur Realisierung hochdynamischer Asynchronmaschinenantriebe mit extrem weitem Feldschwächbereich

The paper presents an inverter concept for the realization of an induction machine drive with an extremely wide constant power range. The stator winding of the induction machine is split up into two isolated and quasi-bifilar wound three-phase winding systems. The series operation of the two winding sets provides very high torque at low stator frequencies while keeping the machine terminal and the inverter DC link current relatively low. However, due to the high number of turns field weakening is necessary at low frequencies (approximately at 50% of rated speed) already. Nevertheless, with the help of an electronic transition from series to parallel stator winding arrangement the machine flux can be restored to its nominal value as given for rated machine speed. Consequently, the break-down torque is increased by a factor of 4 which gives the basis for a high maximum speed with constant machine power.     

VIENNA Rectifier — Grundfunktion und Vergleich hochfrequent getakteter ein- und zweistufiger Dreiphasen-Pulsgleichrichtersysteme mit sinusförmiger Stromaufnahme

In this paper a three-phase PFC PWM rectifier system with low effects on the mains (VIENNA Rectifier 1) which has been developed at the Technical University Vienna in 1994 is described. As compared to conventional rectifier systems the VIENNA Rectifier 1 shows significant advantages such as unity power factor, sinusoidal input current shape (fundamental ohmic mains behavior), controlled output voltage, high efficiency (typically 97%), low costs, high power density and/or low volume, high reliability, and significantly reduced conducted common-mode noise emission. Research is done on this system in companies and universities, e.g. in Europe, U.S.A., Canada, Japan, China and Australia. Furthermore, the paper presents a comparison of a two-stage converter system, which is formed by connecting the VIENNA Rectifier 1 to a DC/DC converter with high frequency isolation (e.g. for applications in uninterruptible power supply systems) and two further developements of the Technical University Vienna which feature single-stage power conversion, i.e. VIENNA Rectifier 2 and VIENNA Rectifier 3.     

HRTEM study of the effect of deformation on the early precipitation behaviour in an AA6060 Al–Mg–Si alloy

The effect of 10% pre-ageing deformation on the early precipitation behaviour in an AA6060 Al–Mg–Si alloy aged 10?min at 190°C was investigated by high-resolution transmission electron microscopy (HRTEM) in ?100?Al projections. The precipitate nucleation was heterogeneous since all precipitates were found to grow on dislocation lines. The pre-ageing deformation suppresses growth of Gunier–Preston zones and β″ phase. The resulting precipitates are still largely coherent with the aluminium matrix. They appear with two main morphologies; one consists of independent, small cross-sections arising from needles with disordered β′ and B′ structures. The other morphology is a much more continuous decoration where precipitates have elongated and conjoined cross-sections and where a particular precipitate phase could not be determined. All precipitates in this work were found to contain a common near-hexagonal sub-cell (SC) with projected bases a?=?b?≈?0.4?nm. This strongly indicates that they are built over the same Si network, which recently has been demonstrated to exist in all precipitates in the Al–Mg–Si(–Cu) system. For the discrete morphology type the network has one hexagonal base vector parallel to or very near a ?510?Al direction. For the continuous type, one base vector falls along a ?100?Al direction. This orientation of the network is different from previous studies of ternary Al–Mg–Si alloys and must be a direct consequence of the deformation.     

Salting out in organic solvents: a new route to carbon nanotube bundle engineering

In this study we investigate salt effects on bundle formation of carbon nanotubes (CNTs) dispersed in an organic solvent, N-methyl-2-pyrrolidone (NMP). Addition of NaI salt leads to self-assembly of CNTs into well-recognizable bundles. It is possible to control the size of the CNT bundles by varying the salt concentration.     

Emission of reactive oxygen species during degradation of iron gall ink

Iron gall inks are characterised by high contents of acids and transition metals, promoting degradation of cellulose due to hydrolysis and oxidation, respectively. Their chemical interaction with the environment is not well understood, especially in view of emissions of degradation products which could lead to spread of degradation processes.In order to study the emissions, we employed gas chromatography/mass spectrometry following headspace micro-extraction, and liquid chromatography following hydroxyl radical scavenging with appropriate probes. We also studied chemiluminescence of cellulose affected by ink degradation.We show that while the emissions of organic volatile degradation compounds by inks are less intense than those of surrounding paper, ink does promote the degradation of cellulose across big distances (from object to object). We were able to link this to emission of reactive oxygen species, probably hydrogen peroxide. Its emission from ink is considerably more intensive than from paper.     

Distributed mixed-signal architecture for programmable smart image sensors

Smart vision systems on a chip are promising for embedded applications. Currently, flexibility in the choice of integrated pre-processing tools is obtained at the expense of total silicon area and fill factor, which are otherwise optimized provided that the sensor performs a specific task. We propose a new architecture based on macropixel-level processing to improve the trade-off by using the same processing elements (PEs) for a whole group of pixels. In this paper, we show through transistor-level simulations the feasibility of using macropixel PEs. Their operative part is analog to avoid the bottleneck of analog to digital converters and has digital control which is distributed in and out of the matrix of pixels. PEs are designed to be suitable for coefficient-reconfigurable spatial and temporal filtering. Sharing electronics among several pixels and matching existing algorithms to the target architecture allow for such programmability without degrading too much pixel area nor fill factor.