Non-oxide ceramic matrix composites for application in hot gas atmospheres – requirements and potential

In spite of the ambitious efforts to increase the portion of alternative and renewable resources the energy production based on fossil fuels will still represent the main part of energy in the next years. Caused by the increasing energy price and the stronger requirements in environmental protection the main focus of future generations of gas turbines will be emphasized on an increased efficiency with a simultaneous reduction of the emissions. From technical point of view these goals can be obtained only by higher hot gas temperatures. Ceramic matrix composites (CMC) offer a high potential for applications as structural parts in advanced gas turbines. During recent years, significant progress in material development of oxide and non-oxide CMC has been achieved, however, there are still considerable deficits especially in the long-term behavior of the materials in hot gas conditions. The present study is focused on the environmental stability of the materials. Caused by the high water vapor pressure in combination with high temperatures and gas velocities, corrosion processes at the surface and inside the materials were observed resulting in significant material degradation and mass loss. Hence, environmental barrier coatings (EBC) have been presented to be the solution to protect the surface of the ceramic materials. Systematic studies on the hot gas corrosion of non-oxide CMC have been performed with and without EBC. Based on a detailed understanding of the processes in the whole system, EBC and the ceramic base material during application in hot gas environments at elevated temperatures, general concepts for the development of environmental barrier coatings will be discussed

High‐resolution structural‐mechanical characterization and simulation of novel barrier coatings

Ceramic matrix composites and non-oxide ceramics are potential near-future materials for high temperature applications in gas turbines for energy production and aviation. Mechanical strength and the capability to withstand temperatures up to 1500 °C under load make these ceramic materials perfect candidates to increase efficiency and to lower emissions. However, corrosive attack by water vapor is still a reliability- and lifetime-limiting factor. Also, thermal insulation is important for oxide ceramic matrix composites because of their low temperature limit in comparison to non-oxide ceramics, e.g. silicon nitride. Therefore, protective coatings are a substantial component in such advanced applications. A new type of coating is investigated which shall act as an environmental and thermal barrier. As a novel approach, a single phase material with high corrosion resistance and low thermal conductivity will be deposited. Solid-state reactions between the substrate material and the coating should provide strong adhesion. In addition, a defined pore distribution should provide good thermal insulation and high tolerance against defects. As a result, a novel, superior coating system is supposed to be achieved for the industrial applications mentioned above. The development of new material systems and coatings requires extensive studies of structure-property relationships and knowledge about the material behavior in dependence on its structure. As a new approach, 3D reconstruction methods will be used to describe the material, using non-destructive micro-X-ray computed tomography and scanning electron microscopy combined with cross-sectioning using a focused ion beam. Especially the non-destructive X-ray technique has the distinct advantage of performing corrosion testing and studying several stages of the evaluation of weak spots in the material-coating system. On the other hand, electron microscopy allows to create 3D images of pores or cracks down to 1 nm resolution in order to improve the understanding of their formation and evolution. Both techniques are well-suited to quantify important structural parameters such as the pore size distribution and pore topology, which can hardly be measured with other methods. The structural information is supplemented by extensive multi-scale mechanical property studies using nano- and microindentation covering the scales from the nano- to the micro-range. To link the multi-scale structural to the multi-scale mechanical material information, both are combined in finite element simulations. With these simulations, the relations between the macroscopic barrier coating properties and the microscopic coating structure will be studied

Macaque models of human infectious disease.

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents-bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease

Entwicklung eines Siliziumnitrid-Werkstoffes für Rotoren in Mikrogasturbinen

The application of structural ceramic parts in gas turbines is supposed to increase efficiency and to decrease emissions. That requires defined knowledge of thermal and mechanical loads as well as a good combination of material and design optimization. Rotating or high-loaded parts have to guarantee reliability even after long-term operation. In this paper the development and assessment of a silicon nitride material for a micro gas turbine will be presented

Entwicklung selbstheilender Materialien zum Korrosionsschutz für Keramiken in Hochtemperaturanwendungen

Keramische Werkstoffe gelten als geeignete Materialien für den Einsatz in den heißen Bereichen von Gasturbinen. Dabei werden auch mechanisch belastete Bauteile adressiert. Ziel ist es, die thermische Belastbarkeit zu erhöhen und damit die Effizienz zu steigern und die Schadstoffemissionen zu verringern. Der im Brenngas enthaltene Wasserdampf führt jedoch zu Korrosionserscheinungen, welche die Lebensdauer beeinträchtigen. Um dies zu verhindern, werden Schutzschichten appliziert. Aufgrund verschiedener Ursachen entstehen in diesen Schutzschichten Risse, welche die Schutzwirkung oder die mechanische Integrität des Bauteils mindern. Gegenstand dieser Arbeit ist deshalb die Erarbeitung und Validierung eines Mechanismus, welcher geeignete Schutzschichtmaterialien in die Lage versetzt, Risse während der Beanspruchung auszuheilen. Der verfolgte Ansatz beinhaltet das Einbringen reaktiver Partikel in eine korrosionsstabile Matrix, welche in Kontakt mit der Brenngasatmosphäre oxidieren und bei gleichzeitiger Volumenzunahme Risse schließen. Dazu werden verschiedene Matrixmaterialien in Kombination mit unterschiedlichen Partikelmaterialien untersucht und die wirksamen Mechanismen beschrieben

Les registrations dans le recueil de préludes de chorals pour orgue de Georg Friedrich Kauffmann Harmonische Seelenlust

Note: CD of performance available from McGill Library upon request.J'ai découvert le nom de Georg Friedrich Kauffmann (1679-1735) lors de mes études doctorales à l'université McGill. Plusieurs de mes lectures mentionnaient son nom en précisant que ce compositeur était à l'origine de la plus abondante source de registrations détaillées pour des oeuvres pour orgue de l'époque baroque. Cependant, en m‟intéressant de plus près à Kauffmann, je me suis aperçu qu'il n'existait que très peu d'études approfondies sur les registrations de ce compositeur. En lisant la thèse doctorale de Theodore van Wyk, publiée en 2005 et ainsi au faîte de la recherche sur Kauffmann, j'ai réalisé qu'une question était régulièrement absente de tous ces travaux musicologiques: pourquoi Kauffmann a-t-il indiqué telles registrations dans tels préludes? En discutant avec le musicologue Bruce Haynes, qui termine actuellement la rédaction de son livre The Pathetick Musician, dans lequel il étudie entre autres les Passions dans les cantates de Johann Sebastian Bach, la réponse à cette question s'est imposée d'elle-même. Il doit certainement exister un lien entre les registrations de Kauffmann et les textes des chorals sur lesquels il a composé ses préludes! En effet, les préludes de Kauffmann sont composés sur des mélodies de chorals luthériens, si bien que le texte de ces chorals est implicite à ces préludes pour orgue seul et apparaît en filigrane. [...

High-velocity water vapor corrosion of Yb-silicate: Sprayed vs. sintered body

The water vapor corrosion of Yb-silicates is of interest to their application as environmental barrier coatings in gas turbine technology. In this study, densified samples from the Yb-silicate powder, as well as plasma-sprayed free-standing Yb-silicate coating were tested at a high-velocity steam rig (T = 1400 °C, v = 90 m/s, PH2O = 0.19 atm) for microstructural comparison. After the test, the measured weight losses of the coatings were larger than that of the densified sample. At the same time, the thicknesses of the corroded scales at the coating surfaces were found to be thicker than that of the sintered sample by a factor of two

Effect of processing on high-velocity water vapor recession behavior of Yb-silicate environmental barrier coatings

The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 μm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript

Hot gas stability of various ceramic matrix composites

This chapter examines the hot gas stability of oxide and non-oxide CMC, fabricated in different institutions of the CCeV in the burner rig of Fraunhofer IKTS Dresden. The tests were performed at 1250 °C and 1400 °C, a gas speed of 100 m/s and a water vapor pressure between 0.2 and 0.25 bar. The chapter also examines microstructure of surface and bulk material after hot gas test in comparison to the as fabricated materials. Various oxide materials were fabricated with hot gas resistant matrix materials, which exhibited superior hot gas stability. Information about the influence of the hot gas test on the mechanical behavior was obtained by comparison of the failure behavior in 3-point bending strength tests on samples prior and after the hot gas test. Embrittlement of the oxide CMC caused by grain coarsening of the ceramic fibers and matrix was observed with increasing test temperature