Investigation of stabilizing agents in thin sol-gel zirconium oxide anti-corrosion coatings on iron materials [Elektronische Ressource] / eingereicht von Ruperto A. Ugas Carrión

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• Publié par: technischen_universitat_darmstadt
• Publié le: 01 janvier 2010
• Nombre de lectures: 143
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Investigation of Stabilizing Agents in Thin Sol-Gel
Zirconium Oxide Anti-corrosion Coatings on Iron
Materials


Vom Fachbereich Chemie
der Technischen Universität Darmstadt



Zur Erlangung des akademischen Grades eines
Doktor-Ingenieurs (Dr.-Ing.)


Dissertation



Ruperto Antonio Ugas Carrión
2010


Investigation of Stabilizing Agents in Thin Sol-Gel
Zirconium Oxide Anti-corrosion Coatings on Iron
Materials


Vom Fachbereich Chemie
der Technischen Universität Darmstadt

zur Erlangung des akademischen Grades eines
Doktor-Ingenieurs (Dr.-Ing.)

genehmigte

Dissertation

eingereicht von

Ruperto Antonio Ugas Carrión, Ing. Quim.
aus Carúpano (Venezuela)


Referent: Prof. Dr. Wolfgang Ensinger
Korreferentin: Prof. Dr. Barbara Albert

Tag der Einreichung: 13.08.2010
Tag der mündlichen Prüfung: 18.10.2010

Darmstadt 2010
D17















Dedicated to my loving mother Josefina
















Acknowledgements

First I would like to thank Prof. Dr. Wolfgang Ensinger, my doctoral advisor, for
giving me the opportunity to begin this investigation on his crew, for his help in
several life occasions, Visa and DAAD support letters, for his comprehension
about my work and for his great help given me the HiWi job necesary for my
financing .

Likewise, I want to express my heartfelt gratitude to Dr. Falk Sittner, my co-
advisor, for his consistent assistance, interest and great help, continous
understanding and opportune observations. I greatly appreciate his patience in
reading my paper manuscripts and thesis and his useful annotations which
improved my thesis.

I would like special acknowledge Prof. Dr. Barbara Albert for her kind
acceptance to act as co-referee of my thesis.
My sincerely thanks to Dr. Stefan Flege for the important SIMS measurements,
his time, advice and for his continuos helpful and technical support in many
opportunities.
I would like to acknowledge Prof. Dr. Hans-Joachim Kleebe, his crew, Frau
Ulrike Kunz for the helpful cooperation with the TEM measurements and to Dr.
Roland Schierholz for his very important support in the crystals analysis.
I am also very thankful to Dr. Joachin Brötz for the countless and important
XRD measurements and for his necessary explanations about the crystalline
structure of my samples.
My special thanks go to Prof. Dr. Michael Reggelin and Frau T. Solms for their
understanding and help with the Promotionskolleg.
I am very thankful to Prof. Dr. Andreas Klein and his crew for the XPS
measurements.
I want to thank Veronika Metje for her great support from the DAAD office





My further Thanks go to:

Dr. Prof. Koumei Baba for his kind cooperation with the plasma ion bean
implantation samples and to Dr. Ruriko Hatada for her collaboration with the
deposition.
Dr. Prof. Victor Carrizales and Dr. Prof. Lucas Álvarez for their support.
Dr. Gunther Kraft for the ESMA analysis and for the good advice and humor.
Brunhilde Thybusch for SEM and microscopical pictures.
Claudia Fasel for the hardness measurements and support with microscopical
images.
Thomas Hermann for his help with SEM images.
Mehdi Yekehtaz, my working collegue, for his kind collaboration with SEM
images and in the electrochemistry laboratory.
Dorotea Berres and Renate Benz for their collaboration in chemistry laboratory
and for the constant support with new bulbs for our light microscop.
Jens von Ringleben for his productive advice and support with EIS
measurements.
Dr. Gerhard Miehe for the allowowance to use his PIES program for some TEM
crystal analysis.
Dr. Ljuba Schmitt and Jens Kling for their help with High Resolution TEM
analysis.
Antje Pappenhagen, our kind secretary, for her assistance during the
administrative procedures.
Eduard Gunnesch for the XPS measurements.
Dr. Olaf Baake for his kind advice
I am also very thankful to all my colleagues at the FG Materialanalytik, FB
Material-und Geowissenschaften, TU-Darmstadt for the friendly and affable
working ambience, helpful collaboration and the great Caferunde.
I would like to thank the government of Venezuela represented through the
Fundación Gran Mariscal de Ayacucho (FUNDAYACUCHO) for the financing of
a great part of my doctoral studies in Germany and to the German Academic
Exchange Service (DAAD) for the financing of my german course and for given


me the great opportunity to make doctoral studies in Germany and to the TU-
Darmstadt for supporting the working materials.

I express my hearty thanks to my loving mother Josefina, my sisters Cruz and
Teresa, my others brother and sisters, my nephews Henry Ugas, Rebeca and
Leonardo, to Sonia Negrau and her family, as well as to Oxana and my friends,
Kathrin, Rudi, Yuly, Danka, Heinrich, Daniel, Juan, Miguel, Manuel Heib, for
their love, comprehension and assistance during my stay in Germany and their
belief in me for the successful ending of this work.























Abstract

Thin protective zirconium oxide coatings prepared via sol-gel with zirconium
propoxide and acetyl acetone (acac) or hydroxypropyl cellulose as stabilizers
have been successfully deposited onto iron substrates at low temperature.
Electrochemical current density vs. potential scans showed a reduction of the
iron dissolution current density and coating porosity in comparison to uncoated
iron, with a strong decrease of these parameters around 5 orders of magnitude
for a HPC concentration = 0.004 g/l. This result is expected as the steric effect
of HPC.
A mixed oxide layer of zirconium and iron was observed in SIMS depth profiles.
The mixed oxide layer thickness showed a dependence on the acac molar ratio.
Increases of acac shorted the overall film thickness, while the mixed oxide layer
was thicker. ZrO -HPC coatings displayed however, a thicker mixed oxide layer 2
and additional increases of the zirconium intensity direct onto substrate surface.
So a higher interdiffusion of zirconium into deeper layers and of iron towards
coating surface was reached.
XRD revealed that the mixed oxide layer is localized between the substrate and
coating surface and possess crystalline structure. At a HPC concentration =
0.004 g/l no ZrO reflexes could be detected. ZrO crystals of 70 nm size were 2 2
identified by TEM in ZrO -acac coatings. However, ZrO -HPC films showed an 2 2
amorphous structure constituted of ZrO and iron oxide containing 2
nanocrystalline zirconium oxide particles immersed in the mixed oxide layer.
The crystals (monoclinic 112) size was between 5 and 10 nm. This result
explains why there were not zirconium oxide reflexes visible in the XRD
analysis. Obviously the ZrO crystalline particles are too small (less than 10 nm) 2
to be detected by XRD so they appear as amorphous material [83]. The
particles are immersed in a compact and amorphous mixed oxide matrix. The
correlation between growth of the mixed oxide phase and decrease of
dissolution current density suggests that it is the mixed oxide phase with
zirconium nanoparticles that is responsible for the reduction of film porosity and
the good corrosion protection properties of the films.



Zusammenfassung

Dünne Zirkoniumoxidschutzschichten auf Basis von Zirkoniumpropoxid mit
Acetylaceton (acac) und Hydroxypropylcellulose (HPC) als Stabilisatoren
wurden erfolgreich durch Sol-Gel-Verfahren synthetisiert und auf
Eisenwerkstoffen bei Raumtemperatur abgeschieden. Potenzialmessungen
zeigten eine Erniedrigung der Stromdichte und der Porosität im Vergleich zu
unbeschichtetem Eisen, wobei die ZrO -HPC-Beschichtungen besonders starke 2
Erniedrigungen um bis zum 5 Größenordnungen zeigten. Dies ist vermutlich ein
Ergebnis des sterischen Effekts von HPC und wurde bei einer optimalen
Konzentration von 0,004 g/l erreicht. In SIMS-Messungen wurde zusätzlich eine
Oxidschicht bestehend aus ZrO und Eisenoxid festgestellt. Die Dicke dieser 2
Oxidschicht weist eine Abhängigkeit von dem Molaranteil des Acetylacetons
auf. Mit ansteigendem Anteil von acac wird die gesamte Schichtdicke dünner
und die Oxidschicht dicker. SIMS-Messungen zeigten ZrO -HPC-Schichten bei 2
den dennoch eine dickere Oxidschicht und zusätzlich einen Anstieg der
Zirkoniumintensitäten direkt auf der Substratoberfläche. Daher findet eine
starke Interdiffusion von Zirkonium in tiefere Schichten und von Eisen in
Richtung der Probenoberfläche statt.
Die kristalline Oxidschicht liegt zwischen Substrat und
Beschichtungsoberfläche, was durch die XRD-Messungen bestätig wurde. Bei