Passivation mechanisms in the initial oxidation of iron by oxygen and water vapor / Sander Jurgen Roosendaal - [S.l.] : [s.n.], 1999 - Tekst. - Proefschrift Universiteit Utrecht

NBC: 33.30: atoomfysica, molecuulfysica: algemeen

Trefwoorden: Iron, oxidation, thin layers, kinetics, composition, iron beam techniques

HR<> Abstract

Iron is the most abundant metal on earth. Steel consist mainly of iron. Moreover, iron is a valuable catalyst and it is important for its magnetic properties. For most of the applications of iron, corrosion (the erosion of the solid by chemical reaction with the environment is an important problem. Oxidation is one of the most important processes involved in corrosion. In the same time, the very thin (several nanometers or less) oxide layers on metal surfaces are of large practical importance: they play a crucial role in the fields of wear and friction, hydrogen embrittlement of stainless steels or poisoning of hydrogen storage materials. Also in the production of modern electronic components by thin-film techniques, the importance of thin oxide films increases, due to the continuous decrease of the dimensions of the structure, down to the nanometer range. Because only a few experimental techniques are sensitive to thin oxide layers between 1 atomic layer and ~100 nm, little is known about the reaction mechanism of the formation of a thin oxide layer and the passivation of iron. Using XPS, ellipsometry and MeV ion beam techniques, we show that the so-called Fromhold-Cook model (FC) for the oxidation may be applied to the initial oxidation of Fe(100) in O2. The FC-model considers the transport of ions and electrons through the oxide layer to the surface of the growing oxide. With this model, we were able to fit the oxidation over a large temperature region (30°C-300°C) and understand the oxidation mechanism: the electronic structure of the oxide is found to influence the oxidation kinetics. The presence of Fe³+ in the oxide formed at T smaller than 150°C leads to passivation. We also studied the oxidation of Fe(100) in H2O. The incorporation of H (OH groups) into the oxide decreases the Fe cation transport through the oxide layer. In conrast with the oxidation in O2, the oxidation kinetics of Fe(100) in H2O is not given by the FC-model. Instead, we could describe the experimental results completely with a nucleation and growth model containing rate equations for surface reactions as teh (complete) dissociation of adsorbed h2O molecules. The oxidation rate increases as oxide islands grow by the dissociation of OH at island edges, and the passivation is complete as the surface becomes completely covered with iron oxide.

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• Title
  
• Contents
  
• Chapter 1: Introduction
  
• Chapter 2: Methods and experimental techniques
  
• Chapter 3: Determination of photoelectron attenuation lenghths in thin oxide films on iron surfaces
  
• Chapter 4: The iron oxide layer grown in O2
  
• Chapter 5: The passivation of iron: application of the Fromhold-Cook model to the initial oxidation of Fe(100) in O2
  
• Chapter 6: The room temperature oxidation of Fe in H2O and H2O/O2 mixtures
  
• Chapter 7: The temperature and pressure dependence of the oxidation of Fe(100) in H2O
  
• Appendix A: Quantitative XPS
  
• Appendix B: A rate equations model for the reaction between H2O vapor and Fe(100)
  
• Bibliography
  
• Summary
  
• Samenvatting
  
• List of publications
  
• Dankwoord
  
• Curriculum Vitae
  
  
• Volledig proefschrift (2.094 kB)