Search

Your search keyword '"Singheiser, Lorenz"' showing total 297 results
Start Over Author "Singheiser, Lorenz"
297 results on '"Singheiser, Lorenz"'

15. Determination of corrosion layers and protective coatings on steels and alloys used in simulated service environment of modern power plants

Author

Nickel, Hubertus, Quadakkers, Willem J., and Singheiser, Lorenz

Subjects
Electric power-plants -- Design and construction, Electric power-plants -- Materials, Power plants -- Design and construction, Power plants -- Materials, Building, Iron and steel -- Properties, Coatings -- Usage, Steel -- Corrosion, Steel -- Analysis, Engineering and manufacturing industries
Abstract

The development of modern power generation systems with higher thermal efficiency requires the use of constructional materials of higher strength and improved resistance to the aggressive service atmospheres. In this paper, the following examples are discussed. (i) The oxidation behavior of 9% Cr steels in simulated combustion gases: The effects of [O.sub.2] and [H.sub.2]O content on the oxidation behavior of 9% Cr steels in the temperature range 600-800[degrees]C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion. In contrast, that in the presence of water vapor, after an incubation period, the scale became nonprotective as a result of a change in the oxidation mechanism. (ii) The development of NiCrAlY alloys for corrosion-resistant coatings and thermal barrier coatings of gas turbine components: The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Considerable efforts have been made in the improvement of the temperature properties of MCrAlY coatings by the additions of minor elements, such as yttrium, silicon, and titanium. The experimental results show the positive, but different influence of the oxidation behavior of the MCrAlY coatings by the addition of these minor elements. (iii) The development of lightweight intermetallics of TiAl-basis: TiAl-based intermetallics are promising materials for future turbine components because of the combination of high-temperature strength and low density. These alloys, however, possess poor oxidation resistance at temperatures above 700[degrees]C. The experimental results showed that the oxidation behavior of TiAl-based intermetallics can be strongly improved by minor additions of 1-2 at. % silver. (iv) The oxide-dispersion-strengthened (ODS) alloys provide excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high-temperature oxidation/ corrosion resistance. The growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with [sup.18]O tracer. The distribution of the oxygen isotopes in the oxide scale was determined by secondary ion-mass spectroscopy and SNMS. The results show the positive influence of a [Y.sub.2][O.sub.3] dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms. [DOI: 10.1115/1.2137769] Keywords: power stations, metallic high-temperature materials, corrosion layers, coatings, SNMS, SIMS, SEM, TEM, EPMA, RBS, LRS, XRD

Published
2006

31. Dislocation microstructures of single crystal ⟨001⟩ CMSX-4 specimens tensile tested at 700 and 1000°C

Author

Schubert, Florian, Penkalla, Heinz-Josef, and Singheiser, Lorenz

Abstract

Two principal methods are used to derive constitutive equations for single crystal Ni-base superalloys: development of a creep potential according the Hill’s theory and the summarization of all activated slip systems: theoretically, the octahedral and the cubic slip system must be considered. An overview of dislocation structure evolution has been performed using transmission electron microscopy (TEM) techniques on 〈001〉-orientated CMSX-4 specimens after tensile tests. The aim of the applied conventional TEM methods was to provide with more details about the influence of temperature and deformation rate on the deformation behaviour of CMSX-4 nickel-base single crystal. A correlation of the γ'phase deformation mechanisms and associated mechanical responses for different tensile testing conditions has been done. With TEM methods the dislocation dipole identification as well as the stacking fault nature has been demonstrated.

Published
2022
Full Text
View/download PDF

32. Slagging and fouling of German lignites based on the association of mineral matter in coal

Author

Beckmann, Michael, Singheiser, Lorenz, Technische Universität Dresden, Thiel, Christopher, Beckmann, Michael, Singheiser, Lorenz, Technische Universität Dresden, and Thiel, Christopher

Abstract

Lignite is still one of the most important energy sources in Germany. In 2017, \SI{24.4}{\percent} of the net electricity production was generated by lignite-fired power plants. The operation of lignite-fired boilers faces challenges such as emission control and slagging and fouling issues. Slagging and fouling issues are caused by inorganic constituents in the coal, also referred to as mineral matter. Mineral matter can be associated with the coal in three different ways: A mineral grain within the coal matrix is referred to as included. A mineral grain that is not asscociated with the organic material is referred to as excluded. In addition, there are inorganic elements that are organically associated with the coal matrix. Due to the reaction front in a burning char particle included particles experience temperatures that can be much higher than what excluded particles experience. Included mineral matter particles also have the potential to coalesce or to react with organically bound elements to form new mineral species Two methods were identified to determine the included and excluded mineral matter in a given coal sample: Float-and-sink analysis and computer controlled scanning electron microscopy (CCSEM). The float-and-sink analysis uses the differences in density between minerals and coal to separate excluded mineral particles from coal particles. CCSEM is an automated SEM-EDS process that allows to analyze a large number of coal particles in a given sample. The SEM uses image analysis to identify coal and mineral particles and to determine the mineral association. Both methods are applied to seven coal samples from three major lignite mining areas in Germany. The results show that in the investgated coals the excluded mineral matter fraction consists mainly of quartz, pyrite/marcasite, clay and gypsum, whereas the included mineral matter fraction is dominated by Ca-S rich minerals. The tendency of slagging and fouling is predicted for all coals on the basis o, Mineralische Bestandteile im Brennstoff sind mitverantwortlich für Verschmutzung- und Ver\-schlack\-ungsvorgänge in mit Braunkohle gefeuerten Kraftwerken. Sie werden durch den Verbrennungsprozess freigesetzt und können sich je nach Eigenschaft der Mineralien an verschiedenen Stellen eines Feuerungsprozesses ablagern. Es wird zwischen mit dem Kohlekorn verwachsenen (internen) mineralischen Partikeln und als eigenständige Partikel vorliegenden (externen) mineralischen Partikeln unterschieden. Weiterhin können anorganische Elemente organisch an die Kohlematrix gebunden sein. Mit der Kohlestruktur verwachsene, interne Partikel sind der Reaktionsfront des brennenden Kohlepartikels direkt ausgesetzt. Sie erfahren höhere Temperaturen als externe Partikel. Höhere Temperaturen fördern das Aufschmelzen der Partikel und beeinflussen so das Ablagerungspotential. Mehrere im Kohlekorn vorliegende mineralische Partikel können beim Abbrennen des Restkokses zu einem Partikel mit neuer chemischer Zusammensetzung verschmelzen. Auch Reaktionen mit den organisch gebundenen mineralischen Elementen sind möglich. Es gibt verschiedene Methoden zur Bestimmung der Bindungsart der Mineralien in der Kohle. Die Schwimm- und Sinkanalyse nutzt die unterschiedlich großen Dichten von externen mineralischen Partikeln, Kohlekörnern mit mineralischen Einschlüssen und reinen Kohlekörnern zur Trennung in einzelne Fraktionen. Eine weitere Methode ist die computergesteuerte Rasterelektronenmikroskopie (CCSEM), mit der die Verteilung mineralischer Partikel im Kohlekorn sowie deren Zusammensetzung bestimmt werden kann. Im Rahmen dieser Dissertation werden beide Methoden auf sieben Kohleproben aus den drei größten deutschen Braunkohleabbaugebieten angewendet. Die Anwendung der Schwimm- und Sinkanalyse und von CCSEM auf die ausgewählten Kohleproben zeigen, dass die externen mineralischen Partikel in den untersuchten deutschen Braunkohlen von Quarz dominiert werden. Weitere signifikante Bestandteile sind Pyrit

Published
2018

34. Modeling of Fe-W phase diagram using first principles and phonons calculations

Author

Jacob, Aurélie, Schmetterer, Clemens, Singheiser, Lorenz S., Gray-Weale, Angus A., Hallstedt, Bengt, Watson, Andrew John A., and Publica

Subjects
DFT calculations, phase diagram
Abstract

In the present work, new descriptions of the thermodynamic properties of the Fe-W system were established based on the Calphad approach using the PARROT module of the Thermo-Calc software. For the present work, existing experimental data from the available literature and own thermodynamic data of the intermediate intermetallic phases based on atomistic computational tools, i.e. density functional theory (DFT) and phonon calculations, were used. Two different phase diagrams of this system were made using the enthalpy of formation data at 0 K from DFT only or the finite temperature Gibbs energies from phonon calculations, respectively, for the description of the end-member Gibbs energies according to the chosen sublattice models.

Published
2015

37. Thermodynamic perspective of Sr‐related degradation issues in SOFCs.

Author

Yin, Xiaoyan, Bencze, Laszlo, Motalov, Vladimir, Spatschek, Robert, and Singheiser, Lorenz

Subjects
SOLID oxide fuel cells, THERMODYNAMICS, CATHODES, MICROSTRUCTURE, ELECTROLYTES, ZIRCONIUM oxide
Abstract

Abstract: (La,Sr)(Co,Fe)O3‐δ is very common as cathode material in SOFC applications. Sr in this type of cathode material is very reactive to form secondary phases with other oxides, which affect micro‐structures and properties of the cathode materials, GDC layers and ZrO2‐based electrolytes. The Sr‐related degradation issues, Cr poisoning and volatile Sr species formation, are studied. As supplement to existing experimental knowledge on Cr poisoning, specific thermodynamic aspects for Cr poisoning are discussed. The thermodynamic calculations show that the partial pressure pCrO3 has a stronger temperature dependence than pCrO2(OH)2, and when considering the reaction between SrO and CrO3(g), dependent on different pCrO3 and pO2, different Sr–Cr–O compounds SrCrO4, SrCrO3, Sr3Cr2O8 or Sr2CrO4 could be formed. In addition, thermodynamic calculations show that in the presence of water vapor, formation of volatile Sr(OH)2 is possible as well. pSr(OH)2 depends on temperature, pH2O and SrO activity and can be of the same order of magnitude as pCrO2(OH)2. Volatile Sr(OH)2 can diffuse through the porous GDC layer and react with ZrO2‐based electrolytes to form SrZrO3 precipitates. The reaction between gaseous Sr species and 8YSZ sheet is studied experimentally. The surface of the 8YSZ sheet is investigated by SEM coupled with EDS, confirming the deposition of Sr. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

49. Cyclic oxidation behaviour of pack aluminized binary and ternary TiAI-base model alloys

Author

Gil, Aleksander, Niewolak, Leszek, Shemet, Vladimir, Singheiser, Lorenz, and Quadakkers, Willem J.

Subjects
technology, industry, and agriculture, equipment and supplies
Abstract

The cyclic oxidation resistance of pack aluminized TiAl-based alloys with additions of Cr, Ni, Nb and Y has been studied . All aluminised materials showed a remarkably lower corrosion attack than the non-coated material. The effect of alloying additions on the microstructure of the coating before and after oxidation was examined. The protective properties of the pack aluminized coating were adversely affected by cracking of the formed TiA13 -phase. The tendency for crack formation appeared to depend on the respective TiAl alloying addition and also on its amount.

Published
2001

50. Thermochemische Untersuchungen zur Hochtemperaturkorrosion in Metallhalogenid-Entladungslampen

Author

Karwath, T., Hilpert, K., and Singheiser, Lorenz

Abstract

Halides of lanthanide are essential components of filling of modern metal halide discharge lamps. These filling made in the arc a line-rich emission spectra in visible region. However this filling are corrosive to Iamp vessel and electrodes. For guarantee the high quality demands to modern light sources, it is necessary to understand the processes during lamp operation. To optimise metal halide lamps to there properties, process behaviour and duration of live there carry out mode) calculations. But this model calculations are only workable if all parameters of lamp process are known. But the mechanism of corrosion in metal halide Iamps are up to now not very known. Aim of this work is by using Knudsen effusion mass spectrometry to simulate the corrosion processes between lamp filling and wall material in metal halide Iamps and to open the corrosion processes to thermo-chemical measurements. This work supply a contribution of knowledge of transport process of SiO$_{2}$ along the wall in quartz-glass discharge vessels. These transport processes are up to now neither quantitatively nor qualitatively understand. In this work are the supposed formation of gaseous silicon-oxy-halides at first time proved, thermo-chemical measured and opened to thermo-chemical calculations.

Published
2000

Catalog

Books, media, physical & digital resources
See catalog results