282 results on '"Stöver, Detlev"'
Search Results
102. Production and Densification of Nanosized Cu/SiC-Powders
- Author
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Vaßen, Robert, primary, Buchner, P., additional, Uhlenbusch, J., additional, and Stöver, Detlev, additional
- Published
- 1998
- Full Text
- View/download PDF
103. Non-destructive characterization of plasma-sprayed ZrO2 coatings by ultrasonic surface waves
- Author
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Schneider, Dieter, primary, Schwarz, Thomas, additional, Buchkremer, Hans-Peter, additional, and Stöver, Detlev, additional
- Published
- 1993
- Full Text
- View/download PDF
104. Wet Powder Pouring
- Author
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Ruder, A., primary, Buchkremer, Hans Peter, additional, Hecker, R., additional, and Stöver, Detlev, additional
- Published
- 1992
- Full Text
- View/download PDF
105. Chemical Compatibility Investigation of Thin-Film Oxygen Transport Membranes on Metallic Substrates.
- Author
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Ye Xing, Baumann, Stefan, Sebold, Doris, Rüttinger, Matthias, Venskutonis, Andreas, Meulenberg, Wilhelm A., and Stöver, Detlev
- Subjects
THIN films ,PEROVSKITE ,OXYGEN ,NICKEL alloys ,SCANNING electron microscopes - Abstract
Thin-film La
0.58 Sr0.4 Co0.2 Fe0.8 O3-δ (LSCF58428) exhibits high oxygen permeability due to its high ionic and electronic conductivity. In order to increase the oxygen flux, a thin-film membrane on a structural substrate is beneficial. Different Ni-based alloys were studied as potential substrate materials. The chemical compositions and thermal expansion coefficients of Nibased alloys were measured in this study. LSCF58428 layers were screen printed on Ni-based alloys and cofired at a high temperature in air. Microstructural and elemental analyses of samples were conducted using a scanning electron microscope and energy-dispersive X-ray spectroscope. X-ray diffraction was used to investigate the phase compositions. The Ni-based alloy, MCrAlY (with M = Ni, Co), with a high Al content showed better chemical compatibility with perovskite material at high temperatures than other Ni-based alloys. A reaction occurred between Sr in the perovskite and the alumina-based surface layer on MCrAlY. However, the reaction zone was found to be stable in mid-term annealing at 800°C in air. Hence, it is expected that this reaction will not prevent application as an oxygen transport membrane. Three different cofiring atmospheres were investigated. Air was found to be the only possible cofiring atmosphere. [ABSTRACT FROM AUTHOR]- Published
- 2011
- Full Text
- View/download PDF
106. Partial Evaporation of Strontium Zirconate During Atmospheric Plasma Spraying.
- Author
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Yanfei Zhang, Mack, Daniel Emil, Jarligo, Maria Ophella, Xueqiang Cao, Vaßen, Robert, and Stöver, Detlev
- Subjects
AERODYNAMIC heating ,PLASMA spraying ,STOICHIOMETRY ,EVAPORATION (Chemistry) ,STRONTIUM ,METAL coating - Abstract
Perovskite-type SrZrO
3 has been investigated as a candidate material for thermal barrier coating application. During plasma spraying of SrZrO3 , SrO volatilized more than ZrO2 and the coating composition deviates from initial stoichiometry. In this investigation, partial evaporation was investigated by spraying SrZrO3 powders into water. The influences of spraying current, distance and particle size of the powder on the partial evaporation were also investigated in a quantitative way. With optimized spraying parameters, stoichiometric SrZrO3 coating was produced by adding an excess amount of Sr in the precursors before plasma spraying to compensate for the volatilized component. [ABSTRACT FROM AUTHOR]- Published
- 2009
- Full Text
- View/download PDF
107. CHARACTERIZATION OF THE RE-OXIDATION BEHAVIOR OF ANODE-SUPPORTED SOFCS.
- Author
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Ettler, Manuel, Menzler, Norbert H., Buchkremer, Hans Peter, Stöver, Detlev, and Forschungszentrum, Jülich
- Subjects
OXIDATION ,FRETTING corrosion ,OXIDATION-reduction reaction ,CHEMICAL reactions ,SOLID oxide fuel cells - Abstract
The article presents a research on the behaviour upon re-oxidation to determine the redox stability of anode-supported of solid oxide fuel cells (SOFCs). The study covered the influences of reoxidation parameters such as temperature, time of re-oxidation, air flow rate and substrate thickness for SOFCs. A list of materials is provided, along with the experimental procedure and discussion topics.
- Published
- 2008
108. Injection moulding of superalloys and intermetallic phases
- Author
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Diehl, Werner, primary and Stöver, Detlev, additional
- Published
- 1990
- Full Text
- View/download PDF
109. Ta2O5/Nb2O5 and Y2O3 Co-doped Zirconias for Thermal Barrier Coatings.
- Author
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Raghavan, Srinivasan, Hsin Wang, Dinwiddie, Ralph B., Porter, Wallace D., Vaβen, Robert, Stöver, Detlev, and Mayo, Merrilea J.
- Subjects
CERAMICS ,CERAMIC materials ,CERAMIC coating ,THERMAL analysis ,MATERIALS science ,INDUSTRIAL chemistry - Abstract
Zirconia doped with 3.2–4.2 mol% (6–8 wt%) yttria (3–4YSZ) is currently the material of choice for thermal barrier coating topcoats. The present study examines the ZrO
2 -Y2 O3 Ta2 O5 /Nb2 O5 systems for potential alternative chemistries that would overcome the limitations of the 3–4YSZ. A rationale for choosing specific compositions based on the effect of defect chemistry on the thermal conductivity and phase stability in zirconia-based systems is presented. The results show that it is possible to produce stable (for up to 200 h at 1000°-1500°C), single (tetragonal) or dual (tetragonal + cubic) phase chemistries that have thermal conductivity that is as low (1.8–2.8W/m K) as the 3–4YSZ, a wide range of elastic moduli (150–232 GPa), and a similar mean coefficient of thermal expansion at 1000°C. The chemistries can be plasma sprayed without change in composition or deleterious effects to phase stability. Preliminary burner rig testing results on one of the compositions are also presented. [ABSTRACT FROM AUTHOR]- Published
- 2004
110. Processing and Properties of Nanograin Silicon Carbide.
- Author
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Vassen, Robert and Stöver, Detlev
- Published
- 1999
- Full Text
- View/download PDF
111. Growth of Boric Acid Crystallites on the Surface of Boron-Doped Silicon Carbide Samples.
- Author
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Vassen, Robert and Stöver, Detlev
- Published
- 1996
- Full Text
- View/download PDF
112. Functionally Graded Thermal Barrier Coatings with Improved Reflectivity and High-Temperature Capability
- Author
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Vassen, Robert, Kassner, Holger, Stuke, Alexandra, Mack, Daniel Emil, Jarligo, Maria Ophelia D., and Stöver, Detlev
- Abstract
Conventional thermal barrier coating (TBC) systems consist of a duplex structure with a metallic bondcoat and a ceramic, heat isolative topcoat. In modern TBCs the ceramic topcoat is further divided into layers with different functions. One example is the double layer system in which conventional yttria stabilized zirconia (YSZ) is used as bottom and new materials as pyrochlores or perovskites are used as topcoat layers. These systems demonstrated an improved temperature capability compared to standard YSZ. Examples of such systems will be shown. In modern gas turbines the increased temperatures and gas pressures lead to an increased fraction of radiative heat flow. Coatings with increased reflectivity can be used to avoid the direct heating of the metallic substrates by this radiation. An effective method to produce such coatings is suspension plasma spraying. These reflective coatings are deposited on top of the TBC system and will lead to a further grading and improved performance of the coating.
- Published
- 2009
- Full Text
- View/download PDF
113. Supported Oxygen Transport Membranes for Oxyfuel Power Plants
- Author
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Betz, Michael, Schulze-Küppers, Falk, Baumann, Stefan, Meulenberg, Wilhelm A., and Stöver, Detlev
- Abstract
Not Available
- Published
- 2006
- Full Text
- View/download PDF
114. Production and Densification of Nanosized Cu/SiC-Powders
- Author
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Vassen, Robert, Buchner, P., Uhlenbusch, J., and Stöver, Detlev
- Abstract
Not Available
- Published
- 1998
- Full Text
- View/download PDF
115. Hydrogenation Behaviour of Some Magnesium-Based Intermetallics in the Temperature Range of 500 to 800 K*
- Author
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Serpekian, Tavit, Stöver, Detlev, and Hecker, Rudolf
- Published
- 1989
- Full Text
- View/download PDF
116. Wasserstoffpermeation durch Chrom
- Author
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Buchkremer, Hans Peter and Stöver, Detlev
- Abstract
Steady state and non-steady state measurements of hydrogen permeation through metallic chromium are reported. The experimentshave been conducted by use of hydrogen and deuterium within a pressure range of 10$^{-8}$ - 1 bar and temperatures between 600 - 800 ° C. Numerical values for the physical quantities permeability, diffusion constant and solubility could be derived. At an upstream pressure above around 10$^{-3}$ bar classical Sieverts-low was found (permeation rate $\backsim$ $\sqrt{p}$) with activation energies Q$_{perm}$ - 65 kJoule/mole, Q$_{Diff}$ = 4-8 kJoule/mole, Q$_{Sol}$ = 57-61 kJoule/mole for the respective processes involved. The isotopic effect between H and D of the permeabilities could be represented by a factor of 1,5 indepent on temperature. All non steady-state measurements could be approximated reasonably well by classical diffusion kinetics. Below up-stream pressures of $\backsimeq$ 10$^{-7}$ bar the kinetics was no longer diffusion controlled, the dependence on up-stream pressure changed from $\sqrt{p}$ $\rightarrow$ p, the activatian energy for permeation increased to 127 kJoule/mole and - the isotopic factor resulted in about 2-3.
- Published
- 1984
117. Ein Versuch zur phänomenologischen Beschreibung der Wasserstoffpermeation durch Stähle und ihre Behinderung durch Oxidfilme
- Author
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Stöver, Detlev, Buchkremer, Hans Peter, and Hecker, R.
- Abstract
Experiments are presented investigating the action of corrosion scales on several steels against hydrogen and tritium permeation. We are interested in such model experiments to learn how to prevent tritium permeation from the primary circuit of an HTR to the secondary side. The same problem might be of some importance in later fusion reactor technology. Our corrosion scales were formed in a temperature range between 500° C and 950° C under varying steam hydrogen mixtures. Thickness of the scales was up to several ym. By adequate choice of the "process" parameters we succeeded to produce oxid scales with relativ high reduction factors for hydrogen permeation as compared with the permeation through the blank metal surfaces. Such scales also show a linear correlation between hydrogen pressure and permeation and an increased activation energy for permeation as compared to that of the blank metal. Our observations cast doubt on elder theories trying to explain the action of oxide films. We try here to apply a formalism presented first by Ash and Barrer to describe our findings. According to our experiments we believe that oxide scales formed under the conditions prevailing here act rather as a "dissociationbarrier" than as a "diffusionbarrier". We try here for the first time to describe the influence of the hydrogen permeation on the tritium permeation of the opposite side, (this is exactly the problem we normally encounter in the case of an HTR for process heat application). Our theoretical explanation shows on the one hand possibilities for producing very high reduction factors e.g. by producing oxide scales on both sides of a heat exchanger tube whereby tritium permeation may be reduced to acceptable levels in a HTR process heat plant, on the other side the models described here, give a sounder base to calculate tritium release in such plants and may be in later fusion reactor blanket configurations.
- Published
- 1982
118. Ausgewählte Arbeiten aus dem experimentellen Bereich des Institutesfür Reaktorentwicklung : Kolloquium anläßlich des 60. Geburtstages von Professor Dr. Rudolf Hecker
- Author
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Filges, D. and Stöver, Detlev
- Abstract
On the Occasion of the 60th birthday of Professor Dr. Rudolf Hecker, director at the Institut für Reaktorentwicklung, the staff members of the Institute arranged a discourse about current research items. On September 9, 1986, dedicated review talks were presented s` arizing the aims of the new research program of the institute. This research is mainly based upon wide earlier experience in high temperature reactor physics and technology, fusion research and spallation physics. The presentations comprised on one side talks about protective layer development and hot isostatic pressing within newly established materials research program of KFA, on the other side talks were presented about high-energy beam materials interaction dealing mainly with computer simulation of particle cascades in matter and their validation by experiments.
- Published
- 1986
119. Teil 1: Experimentelle Bestimmung des Einflusses von Hohlräumen in Moderatormaterialien auf die Diffusionskonstante thermischer Neutronen mit Hilfe der Methode der gepulsten Quellen / Teil 2 : Auswertung von Experimenten zum Diffusionskühlungseffekt nach der Methode von Willers
- Author
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Della Loggia, E., Hecker, R., Stöver, Detlev, Babac, T., and Breitbarth, R.
- Abstract
TEIL I: Bei der Berechnung thermischer Reaktoren ist die Diffusionsweglänge der thermischen Neutronen im Moderator eine wichtige Größe. Obwohl den Moderator im Reaktor normalerweise Kanäle zur Aufnahme der Brennelemente oder für ein Kühlmedium durchziehen, wird in der einfachen Theorie die Diffusionsweglänge für das ungestörte Moderatorsystem benutzt. Selbstverständlich bewirkt aber die Gegenwart von Kanälen, oder anders ausgedrückt, die Abwesenheit von Moderatorsubstanz, eine Vergrößerung der Diffusionsweglänge. Man kann versuchen, diesen Effekt dadurch rechnerisch zu berücksichtigen, daß man eine neue mittlere Dichte des Materials definiert, also den makroskopischen Streuquerschnitt entsprechend dem Hohlraum zu Kompaktstoff-Verhältnis reduziert. Durch eine solche "Homogenisierung" werden aber sich ergebende Anisotropieeffekte nicht berücksichtigt, die z.B. dadurch entstehen, daß längs der Achse eines zylindrischen Kühlkanals eine bevorzugte Diffusion und damit Leckage auftritt. Es sind daher frühzeitig theoretische Untersuchungen angestellt worden, wie man den Einfluß von Hohlräumen auf die Diffusion thermischer Neutronen streng berücksichtigen kann. Eine Schwierigkeit bei diesen theoretischen Berechnungen ergibt sich daraus, daß strenge Lösungen oft nur für bestimmte Geometrien möglich sind, wie z.B. für die Plattengeometrie. Aber auch die Messung der bei Anwesenheit von Hohlräumen veränderten Diffusionslänge mit Hilfe herkömmlicher Techniken ist nicht immer einfach, besonders in dem hier speziell interessierenden Fall des Kerns eines Kugelhaufenreaktors , wo die kugelförmigen Graphitelemente, die den Moderator ausmachen, in statistischer Schüttung- vorliegen. [...] TEIL II : In der Neutronendiffusionstheorie wird das zeitlich veränderliche Neutronenfeld als Überlagerung der Eigenfunktionen gegeben, die Lösungen der Helmholtzgleichung darstellen und an den Extrapolationsgrenzen verschwinden. $\triangledown^{2} \phi_{n} + B^{2}_{n} \phi_{n} = 0 (1) $ Für ein moderierendes System, in welches ein Impuls schneller Neutronen geschossen wurde und in dem die Neutronen thermisches Gleichgewicht erreicht haben, gilt folgender Ansatz: $N(t,\vec{r}) = \sum_{n} A_{n} \cdot \phi_{n}(\vec{r}) \cdot Exp(\gamma_{n} \cdot t) $(2) wobei die kleinste Abklingkonstante $\gamma_{0}$durch folgende Gleichung gegeben ist: $\vert \gamma_{0} \vert = \alpha_{0} + D_{0} \cdot B^{2}_{0} +C \cdot B^{4}_{0} + F \cdot B^{6}_{0}$ (3) Im folgenden Bericht werden Berechnungen der Diffusionsparameter ( $\alpha_{0},D_{0},C,F$ ) aus den Meßwerten eines zeitlich abklingenden Neutronenfeldes vorgenommen. Bei genäherter Darstellung der Meßwerte durch Exponentialfunktionen wurde die Methode von Willers benutzt. Bei der Untersuchung der Diffusionsparameter wurde die Methode der kleinsten Quadrate auf die Funktion $\gamma_{0}(B^{2}_{0})$ angewandt. $B^{2}_{0}$ wurde iterativ aus dem Diffusionsparameter berechnet.
- Published
- 1968
120. Bestimmung des Freisetzungsverhaltens von Helium und Tritium aus neutronenbestrahlten BeO-Sinterkörpern
- Author
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Stöver, Detlev
- Abstract
This report refers to post-irradiation investigations an neutron-irradiated sintered BeO compacts. The macroscopic-mechanical properties of the samples such as density, porosity, and Young's modulus is discussed as well as the radiation damage of both composition and lattice structure. By means of a specially developed vacuum assembly, the release behaviour of helium was studied both isothermal and with a varying function of temperature and time . The detection of tritium is made by an integral method by means of a scintillation spectrometry. An absolute determination of the total contents of helium and tritium in the samples is achieved by a chemical analysis. The results of the measurements are discussed, and they are described quantitatively by the application of a modified diffusion theory .
- Published
- 1972
121. Reactivation of CeMM Tritium Getter-Beds Passivated by Carbon Monoxide*
- Author
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Serpekian, Tavit, primary, Stöver, Detlev, additional, and Hecker, Rudolf, additional
- Published
- 1989
- Full Text
- View/download PDF
122. Authors
- Author
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Otsuka, Tsutomu, primary, Sekimizu, Koichi, additional, Sakamoto, Yasunori, additional, Netsu, Nobuhiko, additional, Yanagisawa, Akio, additional, Niki, Kiyoshi, additional, Kawamura, Atsuro, additional, Oldekop, Werner, additional, Berger, Hans-Dieter, additional, Zeggel, Wilfried, additional, Elter, Claus, additional, Becker, Gerhard, additional, Benocci, C., additional, Buchlin, J-M., additional, Joly, C., additional, Ahmed, Shahid, additional, Clark, R. E., additional, Metcalf, D. R., additional, Rahnema, Farzad, additional, Arif Ahmad, S., additional, Kastenberg, William E., additional, Pomraning, Gerald C., additional, Penndorf, Klaus, additional, Schult, Frank, additional, Bünemann, Dietrich, additional, Mozes, Miriam S., additional, Amian, Win fried, additional, Stöver, Detlev, additional, Bachhuber, Heinz, additional, Bunzl, Kurt, additional, Schimmack, Wolfgang, additional, Gans, Ingbert, additional, Skagius, Kristina, additional, Svedberg, Gunnar, additional, Neretnieks, Ivars, additional, Nevyn Rankin, W., additional, Kemmler, Gerhard, additional, Schlich, Elmar, additional, Macmillan, Norman H., additional, Dooher, George I., additional, Naum, Robert G., additional, Clough, Roger L., additional, Gillen, Kenneth T., additional, Strittmatter, Richard B., additional, Bossi, Richard H., additional, Robinson, Alan H., additional, Barton, John P., additional, Tseng, Chia-Lian, additional, Weng, Pao-Shan, additional, and Lin, Chien C., additional
- Published
- 1982
- Full Text
- View/download PDF
123. Authors
- Author
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Kikuchi, Kenji, primary, Kaburaki, Hideo, additional, Sanokawa, Konomo, additional, Kawaguchi, Katsuyuki, additional, Nemoto, Masaaki, additional, Watanabe, Shintaro, additional, Thiele, W., additional, Lehnert, Günter, additional, Borel, Marc-Olivier, additional, Corthay, André, additional, Fischli, Heinz, additional, Fricker, Hans W., additional, Bennett, Michael J., additional, Houlton, Michael R., additional, Moore, Donald A., additional, Foster, Alan I., additional, Swidzinski, Michael A. M., additional, Quillico, J. J., additional, Despresles, P. J., additional, Schaefer, Josef, additional, Stöver, Detlev, additional, Hecker, Rudolf, additional, Buchkremer, Hans Peter, additional, Jonas, Heinz, additional, Zink, Uwe, additional, Huschka, Hans, additional, Luthardt, Guenther, additional, Portscher, Volker E., additional, Mühlratzer, August, additional, Zeilinger, Hans, additional, Esser, Hans Günter, additional, Kishimoto, Naoki, additional, Tanabe, Tatsuhiko, additional, Araki, Hiroshi, additional, Yoshida, Heitaro, additional, Watanabe, Ryoji, additional, Thiele, Bernd A., additional, Diehl, Hermann, additional, Ohly, Wilhelm, additional, Weber, Heinz, additional, Lindgren, James R., additional, Suzuki, Masahide, additional, Fukaya, Kiyoshi, additional, Kodaira, Tsuneo, additional, Oku, Tatsuo, additional, Watanabe, Katsutoshi, additional, Kondo, Tatsuo, additional, Ogawa, Yutaka, additional, Alberman, A., additional, Bley, G., additional, Pépin, P., additional, Soulat, P., additional, Nickel, Hubertus, additional, Schubert, Florian, additional, Hughes, Peter Thomas, additional, Allen, Donald C., additional, Bodmann, Erik, additional, Breuer, Hans-Jürgen, additional, Raule, Gerhard, additional, Rödig, Manfred, additional, Kitagawa, Masaki, additional, Hattori, Hiroshi, additional, Ohtomo, Akira, additional, Teramae, Tetsuo, additional, Hamanaka, Junichi, additional, Ukikusa, Hiroshi, additional, Penkalla, Heinz-Josef, additional, Over, Hans-Helmut, additional, Goebbels, Klaus, additional, and Kapitza, Harald, additional
- Published
- 1984
- Full Text
- View/download PDF
124. Advances in the Development and Description of Tritium Permeation Barriers in High-Temperature Alloys
- Author
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Buchkremer, Hans Peter, primary, Hecker, Rudolf, additional, Jonas, Heinz, additional, Stöver, Detlev, additional, and Zink, Uwe, additional
- Published
- 1984
- Full Text
- View/download PDF
125. Terms and Results of Hydrogen Permeation Testing of Oxide-Scaled High-Temperature Alloys
- Author
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Schaefer, Josef, primary, Stöver, Detlev, additional, and Hecker, Rudolf, additional
- Published
- 1984
- Full Text
- View/download PDF
126. Diffusion of Silver and Cesium in Silicon-Carbide Coatings of Fuel Particles for High-Temperature Gas-Cooled Reactors
- Author
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Amian, Winfried, primary and Stöver, Detlev, additional
- Published
- 1983
- Full Text
- View/download PDF
127. Authors
- Author
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Hoogen, Norbert G., primary, Merz, Erich R., additional, Burch, William D., additional, Groenier, W. S., additional, Detilleux, E. J., additional, Hild, Werner, additional, Geens, L., additional, Conrad, Rainer P., additional, Merlini, Cesare, additional, Mehner, Alfred-W., additional, Leblanc, J. M., additional, Orlowski, Serge M., additional, Dworschak, Heinz, additional, Hunt, Brian A., additional, Mannone, Francesco, additional, Mousty, Francis, additional, Buchheim, Bernd K., additional, Bunschi, Hans, additional, Hoop, Franz J., additional, Fitzpatrick, James, additional, Zwicky, Hans-Urs, additional, Böhringer, Ian M., additional, Petrik, Ferdinand, additional, Bedenig, Dieter O., additional, Lefevre, Jean F., additional, Hrovat, Milan, additional, Hackstein, Karl-Gerhard, additional, Huschka, Hans, additional, Pirk, H. A., additional, Schmidt-Hansberg, Thomas, additional, Ohga, Yukiharu, additional, Amian, Winfried, additional, Stöver, Detlev, additional, Kodah, Ziad H., additional, Levine, Samuel H., additional, Hughes, Antony E., additional, Marples, J. Angwn C., additional, Stoneham, A. Marshall, additional, Haghighat, Alireza, additional, Robkin, Maurice A., additional, Vigil, Manuel G., additional, Trujillo, Amado A., additional, Yoshimura, H. Richard, additional, Ainscough, John Brian, additional, Coucill, David Norman, additional, Howl, David Anthony, additional, Jensen, Arne, additional, Misfeldt, Ib, additional, Arakawa, Kazuo, additional, Hayakawa, Naohiro, additional, Nakanishi, Hiroshi, additional, Ohe, Toshiaki, additional, Nakaoka, Akira, additional, Athani, V. V., additional, and kumar, L. Vijay, additional
- Published
- 1983
- Full Text
- View/download PDF
128. Cesium Release from Coated Fuel Particles with Failed Coatings
- Author
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Amian, Winfried, primary and Stöver, Detlev, additional
- Published
- 1982
- Full Text
- View/download PDF
129. Nonstoichiometric Y-substituted SrTiO3 materials as anodes for solid oxide fuel cells
- Author
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Ma, Qianli, Tietz, Frank, and Stöver, Detlev
- Subjects
- *
STRONTIUM , *YTTRIUM , *ANODES , *SOLID oxide fuel cells , *STOICHIOMETRY , *TEMPERATURE , *ELECTRIC conductivity , *PEROVSKITE - Abstract
Abstract: Nonstoichiometric yittrium-substituted SrTiO3 samples with a nominal composition of Sr x Y0.07TiO3± δ (x =0.87–1.01) and Sr0.895Y0.07Ti x O3 − δ (x =1.00–1.20) were prepared and investigated. Phase impurities were found in samples with too high A-site or B-site deficiency. The electrical properties of the samples sintered in reducting atmosphere at different temperatures were analyzed with a view to their potential use as anode materials for solid oxide fuel cells (SOFCs). The redox properties of selected samples were investigated in detail. Samples with small A-site deficiency were considered to be the best candidates for SOFC anode materials. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
130. Plasma and Particle Temperature Measurements in Thermal Spray: Approaches and Applications.
- Author
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Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
METAL spraying , *TEMPERATURE measurements , *EMISSION spectroscopy , *TOMOGRAPHY , *PYROMETRY - Abstract
Growing demands on the quality of thermally sprayed coatings require reliable methods to monitor and optimize the spraying processes. Thus, the importance of diagnostic methods is increasing. A critical requirement of diagnostic methods in thermal spray is the accurate measurement of temperatures. This refers to the hot working gases as well as to the in-flight temperature of the particles. This article gives a review of plasma and particle temperature measurements in thermal spray. The enthalpy probe, optical emission spectroscopy, and computer tomography are introduced for plasma measurements. To determine the in-flight particle temperatures mainly multicolor pyrometry is applied and is hence described in detail. The theoretical background, operation principles and setups are given for each technique. Special interest is attached to calibration methods, application limits, and sources of errors. Furthermore, examples of fields of application are given in the form of results of current research work. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
131. Improving Powder Injection in Plasma Spraying by Optical Diagnostics of the Plasma and Particle Characterization.
- Author
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Mauer, Georg, Vaßen, Robert, Stöver, Detlev, Kirner, Stefan, Marqués, José-Luis, Zimmermann, Stephan, Forster, Günter, and Schein, Jochen
- Subjects
- *
POWDER injection molding , *PLASMA spraying , *COATING processes , *MATHEMATICAL optimization , *TOMOGRAPHY , *PARTICLES (Nuclear physics) - Abstract
Powder injection parameters such as gas flow, injection angle, and injector position strongly influence the particle beam and thus coating properties. The interaction of the injection conditions on particle properties based on DPV-2000 measurements using the single-cathode F4 torch is presented. Furthermore, the investigation of the plasma plume by emission computer tomography is described when operating the three-cathode TriplexPro™ torch. By this imaging technology, the three-dimensional shape of the radiating plasma jet is reproduced based on images achieved from three CCD cameras rotating around the plume axis. It is shown how the formation of the plasma jet changes with plasma parameters and how this knowledge can be used to optimize particle injection. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
132. Thin and Dense Ceramic Coatings by Plasma Spraying at Very Low Pressure.
- Author
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Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
SEPARATION of gases , *PLASMA spraying , *ARTIFICIAL membranes , *PEROVSKITE , *CERAMIC coating - Abstract
The very low pressure plasma spray (VLPPS) process operates at a pressure range of approximately 100 Pa. At this pressure, the plasma jet interaction with the surrounding atmosphere is very weak. Thus, the plasma velocity is almost constant over a large distance from the nozzle exit. Furthermore, at these low pressures the collision frequency is distinctly reduced and the mean free path is strongly increased. As a consequence, at low pressure the specific enthalpy of the plasma is substantially higher, but at lower density. These particular plasma characteristics offer enhanced possibilities to spray thin and dense ceramics compared to conventional processes which operate in the pressure range between 5 and 20 kPa. This paper presents some examples of gas-tight and electrically insulating coatings with low thicknesses <50 μm for solid oxide fuel cell applications. Furthermore, plasma spraying of oxygen conducting membrane materials such as perovskites is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
133. From powder properties to fuel cell performance – A holistic approach for SOFC cathode development
- Author
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Tietz, Frank, Mai, Andreas, and Stöver, Detlev
- Subjects
- *
CATHODE rays , *DIRECT energy conversion , *ISOSTATIC pressing , *PEROVSKITE - Abstract
Abstract: This paper provides a short overview on the different aspects of SOFC materials, especially of new cathode materials, ranging from considerations of material properties to long-term phenomena after cell operation. Special emphasis is laid on the reproducible manufacturing of cathode microstructures, which has to be optimised for each individual composition or powder quality. If this is not performed a comparison of various cathode materials can be misleading. The microstructure can be tailored by varying the sintering conditions, which results in different particle sizes. Besides the improvement of power density, the long-term stability of cathodes is discussed in more detail. For (La,Sr)(Co,Fe)O3 (LSCF) cathodes, the predominant factor determining voltage losses during cell operation is the temperature. The mechanism responsible for voltage deterioration is a slow decomposition of the LSCF perovskite due to partial de-mixing of strontium. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
134. Preliminary study on the TriplexPro™-200 gun for atmospheric plasma spraying of yttria-stabilized zirconia
- Author
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Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
PLASMA spraying , *ZIRCONIUM oxide , *CERAMICS , *TEMPERATURE measurements - Abstract
Abstract: The recently introduced three-cathode TriplexPro™-200 atmospheric plasma spray gun was tested with yttria-stabilized zirconia. The effects on the particle characteristics (velocity and surface temperature) were measured by time-of-flight measurement and two-color pyrometry, respectively (DPV-2000 diagnostic system) while the arc current intensity, the plasma gas flow, and its composition were systematically varied. With typical spray parameters of the Triplex® II, using the TriplexPro™-200 with the 9.0 mm nozzle the particle characteristics were found to be almost the same while the nozzle still provides power reserves. In this case, helium may be dispensed with entirely. Using the 6.5 mm or the 5.0 mm nozzle operation is limited to a maximum 500 A current, which significantly increased particle velocities, but it was not possible to keep the particles fully molten. The investigated range of powder grain size (d 50 =58 μm) is to be considered with these parameters. Further possibilities are to be expected with the 6.5 mm and 5.0 mm nozzle using smaller-sized or lower-melting powders. Operating the TriplexPro™-200 gun with the 11.0 mm nozzle and/or nitrogen as secondary plasma gas instead of helium, increased particle temperatures and velocities are achievable. This offers extended possibilities to spray high-melting oxide ceramics like yttria-partially stabilized zirconia. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
135. Synthesis and electrical conductivity of Sr- and Mn-substituted LaAlO3 as a possible SOFC anode material
- Author
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Fu, Qingxi, Tietz, Frank, and Stöver, Detlev
- Subjects
- *
NONMETALS , *PRESSURE , *OXYGEN , *ANODES - Abstract
Abstract: Single phase (La,Sr)(Al,Mn)O3 perovskites were synthesized and their electrical conductivity was studied as a function of temperature and oxygen partial pressure. The electrical conductivity was found to increase with Mn content, temperature and oxygen partial pressure, thus (La, Sr)(Al, Mn)O3 may be regarded as a diluted system of (La,Sr)MnO3. The highest electrical conductivity at 810 °C in air and humidified Ar/4% H2 was observed for (La0.8Sr0.2)0.94Al0.5Mn0.5O3 and reached 12 and 2.7 S/cm, respectively. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
136. Cavitation-resistant NiTi coatings produced by low-pressure plasma spraying (LPPS).
- Author
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Bitzer, Martin, Rauhut, Nadine, Mauer, Georg, Bram, Martin, Vaßen, Robert, Buchkremer, Hans-Peter, Stöver, Detlev, and Pohl, Michael
- Subjects
- *
CAVITATION , *NICKEL-titanium alloys , *METAL coating , *LOW pressure (Science) , *PLASMA spraying , *MECHANICAL wear , *TURBINE blades - Abstract
Cavitation is a severe wear mechanism in technical applications where parts are in contact with rapidly flowing liquids. Examples are turbine blades in hydropower plants or pump components. Coating exposed surfaces with wear-resistant materials is an effective measure for extending lifetime in the case of cavitation attack. NiTi is an attractive material for such coatings considering its clearly pronounced damping behavior based on its pseudoelastic properties. A promising processing route for coating net-shaped components with NiTi is low-pressure plasma spraying (LPPS). In the present work, NiTi layers were produced by LPPS, starting from pre-alloyed NiTi powder. Cavitation resistance was investigated in relation to LPPS parameters, layer thickness and specific surface treatment. Increased cavitation resistance was demonstrated compared to UTP 730, an established cavitation protection material. The study was accompanied by comprehensive characterization of microstructure and phase transformation behavior of the NiTi coatings. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
137. Multi-layer thin-film electrolytes for metal supported solid oxide fuel cells.
- Author
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Haydn, Markus, Ortner, Kai, Franco, Thomas, Uhlenbruck, Sven, Menzler, Norbert H., Stöver, Detlev, Bräuer, Günter, Venskutonis, Andreas, Sigl, Lorenz S., Buchkremer, Hans-Peter, and Vaßen, Robert
- Subjects
- *
ELECTRIC properties of thin films , *SOLID oxide fuel cell electrodes , *CONDUCTIVITY of electrolytes , *SOLID oxide fuel cell manufacturing , *PHYSICAL vapor deposition , *GAS flow - Abstract
Abstract: A key to the development of metal-supported solid oxide fuel cells (MSCs) is the manufacturing of gas-tight thin-film electrolytes, which separate the cathode from the anode. This paper focuses the electrolyte manufacturing on the basis of 8YSZ (8 mol.-% Y2O3 stabilized ZrO2). The electrolyte layers are applied by a physical vapor deposition (PVD) gas flow sputtering (GFS) process. The gas-tightness of the electrolyte is significantly improved when sequential oxidic and metallic thin-film multi-layers are deposited, which interrupt the columnar grain structure of single-layer electrolytes. Such electrolytes with two or eight oxide/metal layers and a total thickness of about 4 μm obtain leakage rates of less than 3 × 10−4 hPa dm3 s−1 cm−2 (Δp: 100 hPa) at room temperature and therefore fulfill the gas tightness requirements. They are also highly tolerant with respect to surface flaws and particulate impurities which can be present on the graded anode underground. MSC cell tests with double-layer and multilayer electrolytes feature high power densities more than 1.4 W cm−2 at 850 °C and underline the high potential of MSC cells. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
138. Failure mechanisms of magnesia alumina spinel abradable coatings under thermal cyclic loading.
- Author
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Ebert, Svenja, Mücke, Robert, Mack, Daniel, Vaßen, Robert, Stöver, Detlev, Wobst, Tanja, and Gebhard, Susanne
- Subjects
- *
MAGNESIUM oxide , *ALUMINUM oxide , *THERMOCYCLING , *JET engines , *CYCLIC loads , *CERAMIC coating , *GAS turbines , *FAILURE analysis - Abstract
Abradable coatings have been used in low- and high-pressure sections of jet engine compressors for more than 40 years. Today, they are also used in the high-pressure turbine of jet engines and are gaining more interest for applications in industrial gas turbines. They minimise the clearance between the rotating blade tips and the stationary liners. Aside from being abradable, the coatings have to be mechanically stable and withstand high thermo-mechanical loadings. A typical material used in engines today is yttria-stabilised zirconia (YSZ). This material advantageously combines a suitable thermal conductivity with a high thermal expansion coefficient, but shows a temperature capability limited to 1200°C in long-term applications. Typical abradable coating thicknesses are above 1mm. With increasing coating thickness and limited cooling efficiency leading to high surface temperatures, there is a risk of premature failure. As a result, new ceramic materials have been developed with better high-temperature capability. The present work investigates an atmospheric plasma sprayed ceramic double-layer coating system composed of 7YSZ as an intermediate layer and magnesia alumina spinel as a top layer. This double-layer system was sprayed onto disc-shaped Inconel 738 superalloy substrates, which were coated with a vacuum plasma sprayed MCrAlY bondcoat. The lifetime of the coating system was assessed via thermal gradient cycling testing with surface temperatures above 1400°C. During cycling, the samples showed a typical failure mechanism with exfoliation of thin coating lamellae starting from the coating surface. This failure mechanism was not observed in thermal barrier or abradable coatings in the past. The failure mechanism was analysed and mismatch stress calculations were carried out. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
139. Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6-xWO12-y.
- Author
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Seeger, Janka, Ivanova, Mariya E., Meulenberg, Wilhelm A., Sebold, Doris, Stöver, Detlev, Scherb, Tobias, Schumacher, Gerhard, Escolástico, Sonia, Solís, Cecilia, and Serra, José M.
- Subjects
- *
LANTHANUM compounds , *PROTONS , *SUBSTITUTION reactions , *SEPARATION of gases , *MEMBRANE separation , *SINTERING , *ELECTRIC conductivity - Abstract
Mixed proton-electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic-electronic conductivity. Lanthanum tungstate La6-xWO12-y (with y = 1.5x + δ and x = 0.5-0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6-xWO12-y and for all substituted La6-xWO12-y compounds was measured in the temperature range of 400-900 °C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
140. Novel high-performance solid oxide fuel cells with bulk ionic conductance dominated thin-film electrolytes
- Author
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Han, Feng, Mücke, Robert, Van Gestel, Tim, Leonide, André, Menzler, Norbert H., Buchkremer, Hans Peter, and Stöver, Detlev
- Subjects
- *
SOLID oxide fuel cells , *ELECTRIC conductivity , *THIN films , *ELECTROLYTES , *WETTING , *ELECTROCHEMICAL analysis , *IMPEDANCE spectroscopy , *MICROFABRICATION - Abstract
Abstract: The overall performance of ionic conducting electrolyte layers is a key factor for determining the power density of solid oxide fuel cells (SOFCs). The aim of this work is to investigate high performance SOFC electrolyte layers developed in our lab via a low cost wet-chemical processing method. In this paper, SOFCs with bulk ionic conductivity dominated thin-film electrolyte demonstrate superior electrochemical performances. Conventional materials for SOFCs are applied in this work: Ni–YSZ cermet as the anode, yttria-stabilized zirconia (YSZ) as the electrolyte, gadolinia-doped ceria (CGO) as the Sr-diffusion barrier layer, and LSCF or LSC as the cathode. At 0.7 V and 600 °C, single cells with an active LSCF and LSC cathode area of 4 × 4 cm2 obtain a power density of 0.7 and 1.4 W cm−2, respectively. According to electrochemical impedance spectroscopy (EIS), the ohmic resistance of the single cells is almost one order of magnitude lower than the conventionally fabricated SOFCs. Due to the improved performance of the electrolyte, SOFCs are able to deliver high power output at reduced operating temperature and increased cell voltage. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
- View/download PDF
141. Improving Atmospheric Plasma Spraying of Zirconate Thermal Barrier Coatings Based on Particle Diagnostics.
- Author
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Mauer, Georg, Sebold, Doris, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
THERMAL barrier coatings , *PLASMA spraying , *LANTHANUM compounds , *ZIRCONIUM compounds , *PARTICLE motion , *STOICHIOMETRY , *PYROCHLORE - Abstract
Lanthanum zirconate (LaZrO) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of LaZrO a considerable amount of LaO can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the LaO-ZrO system, in the composition range of pyrochlore structure, the stoichiometric LaZrO has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro™-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on gadolinium zirconate (GdZrO) were included, which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings that show good thermal cycling performance. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
142. Characteristics of Ceramic Coatings Made by Thin Film Low Pressure Plasma Spraying (LPPS-TF).
- Author
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Hospach, Andreas, Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
PLASMA spraying , *CERAMIC coating , *PHYSICAL vapor deposition , *THIN film capacitors , *SUBSTRATES (Materials science) - Abstract
The thin film low pressure plasma spray process (LPPS-TF) has been developed with the aim of efficient depositing uniform and thin coatings with large area coverage by plasma spraying. At high power input (~150 kW) and very low pressure (~100 Pa) the plasma jet properties change considerably and it is even possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This relatively new technique bridges the gap between conventional plasma spraying and physical vapor deposition. In addition, the resulting microstructures are unique and can hardly be obtained by other processes. In this paper, microstructures made by LPPS-TF are shown and the columnar layer growth by vapor deposition is demonstrated. In addition to the ceramic materials TiO, AlO or MgAlO, the focus of the research was placed on partially yttria-stabilized zirconia. Variations of the microstructures are shown and discussed concerning potential coating applications. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
143. Deposition and Characteristics of Submicrometer-Structured Thermal Barrier Coatings by Suspension Plasma Spraying.
- Author
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Guignard, Alexandre, Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
THERMAL barrier coatings , *SUBSTRATES (Materials science) , *PLASMA spraying , *PLASMA diffusion , *ISOSTATIC pressing - Abstract
In the field of thermal barrier coatings (TBCs) for gas turbines, suspension plasma sprayed (SPS) submicrometer-structured coatings often show unique mechanical, thermal, and optical properties compared to conventional atmospheric plasma sprayed ones. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. Experimental results showed the capability of SPS to obtain yttria stabilized zirconia coatings with very fine porosity and high density of vertical segmentation cracks, yielding high strain tolerance, and low Young's modulus. The evolution of the coating microstructure and properties during thermal cycling test at very high surface temperature (1400 °C) in our burner rigs and under isothermal annealing was investigated. Results showed that, while segmentation cracks survive, sintering occurs quickly during the first hours of exposure, leading to pore coarsening and stiffening of the coating. In-situ measurements at 1400 °C of the elastic modulus were performed to investigate in more detail the sintering-related stiffening. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
144. Decomposition of Ba(Mg1/3Ta2/3)O3 perovskite during atmospheric plasma spraying
- Author
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Jarligo, Maria Ophelia, Mauer, Georg, Sebold, Doris, Mack, Daniel Emil, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
CHEMICAL decomposition , *BARIUM oxide , *PEROVSKITE , *PLASMA spraying , *ATMOSPHERIC chemistry , *THERMAL conductivity , *THERMAL barrier coatings - Abstract
Abstract: Perovskite Ba(Mg1/3Ta2/3)O3, BMT has promising bulk properties (thermal conductivity ~2W/m-K and coefficient of thermal expansion ~11×10−6/K at 1473K) for thermal barrier coating (TBC) applications at high temperature. However, during atmospheric plasma spraying (APS), such material was found to lose constituents due to the differences of vapor pressures resulting to non-stoichiometric composition of deposited coatings. To investigate the extent of phase decomposition at spray distance and varying electric arc current, different feedstock powders were plasma sprayed into water and collected for chemical, microstructural and phase analyses. When the electric arc current was decreased from 500A to 300A, the decomposition of the powders was reduced and the microstructure of the deposited coatings was improved. The thermal cycling lifetime of the deposited coatings at ~1250°C surface temperature is also higher. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
- View/download PDF
145. Review of New Developments in Suspension and Solution Precursor Thermal Spray Processes.
- Author
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Killinger, Andreas, Gadow, Rainer, Mauer, Georg, Guignard, Alexandre, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
COATING processes , *METAL spraying , *PLASMA spraying , *NANOSTRUCTURED materials , *SURFACES (Technology) , *RAW materials - Abstract
Thermal spray coatings from liquid feedstock such as suspensions and solution precursors have received increasing interest due to the unique coating properties obtainable by these processes. Several research groups are working on the basis of plasma as well as on high-velocity oxy-fuel approaches to manufacture advanced nanostructured and nanophased materials. These activities are reflected in various recent publications and conference presentations about feedstock preparation, equipment and process design, modeling techniques, in-process diagnostics, coating characterization, and emerging applications. This article will review these recent developments to give an up-to-date overview and to trace the current trends. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
146. Nano-structured solid oxide fuel cell design with superior power output at high and intermediate operation temperatures.
- Author
-
Van Gestel, Tim, Feng Han, Sebold, Doris, Buchkremer, Hans Peter, and Stöver, Detlev
- Subjects
- *
NANOSTRUCTURED materials , *SOLID oxide fuel cells , *PROPERTIES of matter , *TEMPERATURE , *THIN films - Abstract
solid oxide fuel cell (SOFC) with a thin-film yttria-stabilized zirconia (YSZ) electrolyte was developed and tested. This novel SOFC shows a similar multilayer set-up as other current anode-supported SOFCs and is composed of a Ni/8YSZ anode, a gas-tight 8YSZ electrolyte layer, a dense Sr-diffusion barrier layer and a LSCF cathode. To increase the power density and lower the SOFC operating temperature, the thickness of the electrolyte layer was reduced from around 10 μm in current cells to 1 μm, using a nanoparticle deposition method. By using the novel 1 μm electrolyte layer, the current density of our SOFC progressed to 2.7, 2.1 and 1.6 A/cm at operation temperatures of 800, 700 and 650°C, respectively, and out-performs all similar cells reported to date in the literature. An important consideration is also that cost-effective dip-coating and spin-coating methods are applied for the fabrication of the thin-film electrolyte. Processing of 1 μm layers on the very porous anode substrate material was initially experienced as very difficult and therefore 8YSZ nanoparticle coatings were developed and optimized on porous 8YSZ model substrates and transferred afterwards to regular anode substrates. In this paper, the preparation of the novel SOFC is shown and its morphology is illustrated with high resolution SEM pictures. Further, the performance in a standard SOFC test is demonstrated. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
147. Columnar-Structured Thermal Barrier Coatings (TBCs) by Thin Film Low-Pressure Plasma Spraying (LPPS-TF).
- Author
-
Hospach, Andreas, Mauer, Georg, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
THERMAL barrier coatings , *METAL coating , *METAL spraying , *COATING processes , *MICROMECHANICS - Abstract
The very low-pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with coverage of a large area by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low-pressure plasma-spraying processes (LPPS) operating at 5-20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters, it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar-structured TBCs. However, the deposition rate is low, and the line-of-sight nature of the process involves specific restrictions. In this article, the deposition of TBCs by the LPPS-TF process is shown. How the evaporation of the feedstock powder could be improved and to what extent the deposition rates could be increased were investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
148. A novel test approach for plasma-sprayed coatings tested simultaneously under CMAS and thermal gradient cycling conditions
- Author
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Steinke, Tanja, Sebold, Doris, Mack, Daniel E., Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
PLASMA spraying , *CERAMIC coating , *HIGH temperatures , *CALCIUM compounds , *THERMAL barrier coatings , *MICROSTRUCTURE - Abstract
Abstract: Plasma-sprayed ceramic coatings, used as thermal barrier or abradable coatings in high-pressure stages of gas turbines, are exposed to high thermo-mechanical loading due to harsh operating conditions. Under certain conditions they also have to withstand attack by calcium-magnesium-alumino-silicate (CMAS) deposits resulting from the ingestion of siliceous minerals with the intake air. Resistance to this kind of attack becomes more important at higher temperatures, when the melting temperature of the CMAS deposits is exceeded and a penetration into the coating microstructural features (cracks and pores) can take place. During cooling the CMAS solidifies and the coating loses its strain tolerance, which can lead to coating failure. Although the basic principles of failure seem to be understood, a detailed analysis of the mechanisms and the possibilities of avoiding delamination are still lacking, especially because there are as yet no adequate test beds. This paper investigates the possibility of testing such coatings in a burner rig test facility under thermal gradient cycling conditions and at the same time CMAS deposition. This novel and unique test approach promises a coating screening and characterization test under service conditions. The CMAS rig was established because the test conditions simulated here are closer to actual engine conditions, as compared to previous tests with primarily CMAS deposition and subsequent thermal furnace testing. The experimental setup of this new test approach is described and the applicability is confirmed. Furthermore, a first evaluation for plasma-sprayed coatings is presented. A significantly reduced lifetime was found for samples tested with CMAS attack in comparison to tests with water deposition only. The lifetime was also reduced compared to older results without any corrosive media. A decrease of nearly two orders of magnitude was found. A microstructural evaluation of the coatings is presented and the mechanisms and reasons for the very early failure are discussed. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
149. Process diagnostics in suspension plasma spraying
- Author
-
Mauer, Georg, Guignard, Alexandre, Vaßen, Robert, and Stöver, Detlev
- Subjects
- *
PLASMA diagnostics , *SUSPENSIONS (Chemistry) , *PLASMA spraying , *ZIRCONIUM oxide , *THERMAL barrier coatings , *EMISSION spectroscopy , *PLASMA injection , *EVAPORATION (Chemistry) , *SOLIDIFICATION - Abstract
Abstract: Benefits and limitations of process diagnostics are investigated for the suspension plasma spraying of yttria-stabilized zirconia thermal barrier coatings. The methods applied were enthalpy probe measurements, optical emission spectroscopy, and in-flight particle diagnostic. It was proved that the plasma characteristics are not affected negatively by the injection of the ethanol based suspension since the combustion of species resulting from ethanol decomposition achieves a gain of plasma enthalpy. Furthermore, the conditions of the suspension injection into the plasma were found to be optimum as a significant content of evaporated powder material could be detected. Regarding the void content and segmentation crack density of the coatings, the in-flight particle diagnostic showed that the spray distance should be dimensioned in a way that the molten particles reach the substrates just before solidification starts. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
150. Overview on advanced thermal barrier coatings
- Author
-
Vaßen, Robert, Jarligo, Maria Ophelia, Steinke, Tanja, Mack, Daniel Emil, and Stöver, Detlev
- Subjects
- *
THERMAL barrier coatings , *CERAMIC materials , *OXIDES , *ZIRCONIUM oxide , *TEMPERATURE effect , *SUBSTITUTION reactions , *GAS turbines , *ALUMINATES , *LITERATURE reviews - Abstract
Abstract: During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200°C which necessitates its substitution in advanced gas turbines. In the paper an overview is tried on different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double-layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
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