Oxidation and wet wear of silicon carbide [Elektronische Ressource] / vorgelegt von Volker Presser

Volker Presser

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2009
• Nombre de lectures: 21
• Langue: English
• Poids de l'ouvrage: 16 Mo

Extrait

OXIDATION AND WET WEAR

OF SILICON CARBIDE








Dissertation zur Erlangung des Grades eines
Doktors der Naturwissenschaften
der geowissenschaftlichen Fakultät
ddeerr EEbbeerrhhaarrdd-Karls-UUnniivveerrssiittäätt TTüübbiinnggeenn



vorgelegt von
2009 Volker Presser
aus Immenstadt




OXIDATION AND WET WEAR
OF SILICON CARBIDE





Dissertation

zur Erlangung des Grades eines Doktors der Naturwissenschaften







der Geowissenschaftlichen Fakultät
der Eberhard-Karls-Universität Tübingen








vorgelegt von
Volker Presser
aus Immenstadt

2009

























Tag der mündlichen Prüfung: 17.06.2009
Dekan: Prof. Dr. Peter Grathwohl
1. Berichterstatter: Prof. Dr. Klaus G. Nickel
2. Berichterstatter: Dr. Christoph Berthold
3. Berichterstatter: Prof. Dr. Yury Gogotsi




“I am among those who think that science has great beauty.
A scientist in his laboratory is not only a technician:
he is also child placed before natural phenomena
which impress him like a fairy tale.”



Marie Skłodowska–Curie (1867 - 1934)


ACKNOWLEDGEMENTS


ACKNOWLEDGEMENTS:

This work was financially supported by the German Research Foundation DFG (grant number
Ni299/12-1) and partially from my Bernd-Rendel-award prize money.
First of all I would like to thank my advisor and dear mentor Prof. Klaus Georg Nickel for giving me the
chance to work on this interesting project and also for the possibility to participate on numerous confe-
rences, collaborations and side projects - and of course for all of his kind help and support! Also, Dr.
Christoph Berthold is gratefully thanked for his help. This work would not have been possible without his
input and support - both work-related and work-unrelated. Thank you, Christoph!
Also, none of this work could have been carried out without sample material. For that, I would like to
thank ESK ceramics GmbH (Kempten) and SiCrystal AG (Erlangen) for the kind supply of sintered SiC
bodies (ESK) and SiC single crystals (SiCrystal), respectively. And of course special thanks to our master
mechanics Norbert Walker and Barbara Maier and their team along with Indra Gill-Kopp for all their
help and preparing such small sample volumes even specialized companies thought impossible. Our work-
shop was always the best address to turn to solve “unsolvable” problems and to get access to sample
holders or tools “impossible to build”.
I owe special thanks to Dr. Richard Wirth who played a major role in the sub-micrometer scale characte-
rization of tribolayers using FIB for sample preparation and HR-TEM / EDX / EELS for sample characteri-
zation. This technique along with his skillful practice opened a whole new dimension in triboscale analysis.
Also, I like to express my gratitude also to the GeoForschungsZentrum Potsdam (now Helmholtz-Zentrum
Potsdam) for letting me conduct my research free of charge.
Our department’s secretary, Dagmar Dimitrovice, is gratefully thanked for thoroughly dealing with all
the organizational work and giving the very best example of how kind and friendly a bureaucrat can
be.
For the introduction into HDAC operations I would like to thank Dr. Andreas Audétat (Bayerisches Geoins-
titut Bayreuth) and of course Prof. Hans Keppler for kindly putting his laboratory equipment in Tübingen
at my disposal.
Dr. Christoph Glotzbach is thanked for introducing me to the field of age determination and his kind help
and helpful input throughout our valued and successful collaboration.
Dipl.-Chem. Christoph Raisch is thanked for conducting XPS measurements and his help during the inter-
pretation phase.
Thanks also to my colleagues at the Fraunhofer IWM in Freiburg - Dr. Andreas Kailer and Dipl.-Min.
Oliver Krummhauer - for covering the simulation part and conducting tribometer experiments.
The helpful and greatly appreciated input of so many others for the individual papers presented in this
cumulative thesis is acknowledged in detail in the corresponding sections.





OXIDATION AND WET WEAR OF SILICON CARBIDE Page i



ABSTRACT


ABSTRACT:
Silicon carbide (SiC) as both the most important non-oxide ceramic and promising semiconductor material
grows stoichiometric SiO as its native oxide during hot-gas corrosion (= passive oxidation). During SiC 2
oxidation, there are many influencing parameters, for example, porosity, presence of sintering aids, im-
purities, crystallographic orientation, subsequent surface treatment, and atmospheric composition. Also,
the initially vitreous silica scale undergoes structural transformation during crystallization as disc-like devi-
trification areas appear (radialites). These areas show significantly decreased oxidation rates due to
decelerated gas diffusion. Impurities, for example, originating from the furnace atmosphere, accumulate
over time on the silica scale and lead to a second morphological transition due to a melt-catalyzed re-
crystallization. In the end, small crystalline spheres (globulites) appear which are separated by a signifi-
cant pore volume. The latter acts as pathway for accelerated gas diffusion causing higher oxidation
rates. Therefore, the kinetics can be complex.
Nonetheless, a general linear-parabolic time-law can be found for most SiC materials for passive oxida-
tion. The pronounced anisotropy of SiC expresses itself by quite different oxidation rates for the various
crystallographic faces that vanish approximately at 1350° - 1400°C. Manifold impact factors are re-
flected by oxidation rate-constants for silicon carbide that vary over orders of magnitude. The under-
standing of SiC oxidation and silica formation is still limited; therefore, different oxidation models are
presented and evaluated in light of current knowledge.
Silicon carbide sustains chemical and mechanical deterioration during tribological exposure under water
lubrication. Hydrothermal treatment alone only leads to active corrosion of SiC while tribochemical wear
causes the formation of a thin (tens to hundreds of nanometer) layer composed of nanoscale SiC wear
debris embedded in a silica-like matrix (SiOxHy) with possibly some minor oxycarbidic content. The SiC
wear particles are plastically deformed and rounded as a result of mechanical tribolapping. Below that
layer, subsurface damage builds up in the form of dislocations, ruptures and shear cracks. As a result of
plastic deformation (similar to indentation plasticity) SiC single crystals within that transition zone are
transformed into mosaic crystals with smaller domains due to slip plane gliding.
A first qualitative wear model combines hydrothermal corrosion with mechanical wear. While mechanical
contact yields pathways for water inflow and generally disrupts the structural integrity of SiC grains,
hydrothermal reactions of trapped water and subsequent pressure relief leads to a mechanism of disso-
lution and reprecipitation. The latter produces the observed amount of SiO H which acts as an adhesive x y
for the SiC wear debris.
As for analytical methods, tribologically influenced ceramic surfaces are usually only looked at in terms
of the wear effects: surface topography, friction coefficient, loss rates. Current efforts go towards a
deeper understanding of mechanisms and kinetics. To gain this, the effects of the wear of ceramics on the
phases and microstructures have to be analyzed in detail. Because structural changes occur within the
uppermost Nm and tribochemical reaction layers are often restricted to the nm-range, appropriate ana-
lytical tools have to be used and those come only now available. This study shows how the currently de-
veloped techniques of X-ray microdiffraction combined with Raman spectroscopy can resolve many is-
sues. Another recent improvement, transmission electron microscopy (TEM) on cross sections prepared via
the focused ion beam technology (FIB), helps to verify the findings of the former techniques.




Page ii OXIDATION AND WET WEAR OF SILICON CARBIDE



ZUSAMMENFASSUNG


Zusammenfassung:
Siliziumkarbid (SiC) ist sowohl die wohl bedeutendste Nichtoxidkeramik aber auch als Halbleiter ein viel-
versprechendes Material. Gaskorrosion in Gegenwart von Sauerstoff führt dabei als einzige feste Phase
zu Bildung von SiO (passive Oxidation). Hierbei spielen jedoch viele Einflussfaktoren eine wichtige Rolle, 2
wie zum Beispiel Porosität, Sinteradditive, Verunreinigungen, die kristallographische Orientierung, vor-
hergehende Oberflächenbehandlung und die chemische Zusammensetzung der oxidierenden Atmosphäre.
Als Fol