Several technical processes in chemical process industries, waste incineration and gasification as well as energy conversion suffer from severe materials problems arising from high temperature gaseous chlorine attack or induced by molten deposits on the material surface. In recent time new approaches have come up in describing and modelling the mechanisms of corrosion and concerning the type of materials regarded. In particular significant work has been started on the behaviour of ceramic materials under such conditions. Both ceramic and metallic materials will be addressed in this session.

• Michael McNallan, University of Illinois
  High Temperature Corrosion of Ceramics by Chlorine and Chloride Vapors
• Michael Spiegel, Max-Planck-Institut für Eisenforschung
  Corrosion by Chloride and Sulphate Melts

The oxide scales which form on high temperature materials during service and which protect the metal against accelerated corrosion are of brittle ceramic nature. Under service conditions they may crack and loose their protective effect. During the last years a large investigation program was performed as a cooperative action of several national laboratories in the US dealing with stresses in oxide scales and with the scale failure mechanisms. The results of this program form the basis of one of the two talks. The other talk which comes from one of the joint research centers of the European Union addresses the view and the results of the European activities in relation to the international state-of-the-art.

• Peggy Hou, LBNL
  Stresses in Al₂O₃ Scales and their Effects on Scale Cracking and Spallation
• Victor Guttmann, Joint Research Centre, Petten
  Oxide Scale Failure Mechanisms - Interaction of Physical Defects and Mechanical Stresses

• Poster Session

Until recently it has mostly been neglected that from the high temperature corrosion point of view life-time of materials is first of all determined by alloy depletion processes in the metal subsurface zone. During the last years several efforts have taken place to model these depletion processes quantitatively and, thus, supply a basis for an end-of-life assessment for high temperature materials and coatings. The two contributions introduce the mechanisms and recent developments on modelling.

• Hugh Evans, University of Birmingham
  Solute Depletion and the Initiation of Breakaway Oxidation
• Brian Gleeson, Iowa State University
  The Consequences and Manifestations of Subsurface Depletion

Allthough thermal barrier coatings on metallic components like gas turbine parts are now in use for more than a decade there still are severe problems with adhesion of the ceramic top layer. Extensive work with NASA and other laboratories has shown that it is mainly the oxidation processes underneath the ceramic top layer which limit life-time. Recent work led to interesting new approaches concerning the understanding of the role of oxidation in adhesion of the ceramic top layer and to the development of bond coat free TBC systems.

• Jim Smialek, NASA Lewis
  Oxidation Behaviour of Low Sulfur Superalloys under Plasma Sprayed TBC's
• Vladimir Tolpygo, UCSB
  Oxidation of Platinum Aluminide Bond Coats and Adhesion of EB-PVD TBC

• Poster Session

Materials of this type are primarily used for applications in modern aerospace engineering but also in chemical and nuclear industries. A primary concern is their high sensitivity in oxidizing environments at high temperatures. New results exist on the mechanisms of oxidation of these materials and on the inhibition of oxidation. In the session such results and models will be presented from work in a European aerospace research laboratory and at a US university.

• Marie-Pierre Bacos, ONERA
  Oxidation of Carbon/Carbon Composites
• Ljubisa Radovic, Penn State University
  Oxidation of Carbon/Carbon Composite Materials: An Example of Macroscopic Complementarity

Even today new surprising effects in oxidation can be found in particular for new groups of materials. This is true e.g. for titanium aluminides which are of high interest in energy conversion and jet industry as materials replacing the nickel-base alloys in certain parts. The microalloying effect based on the addition of „homeopathic" doses of usually detrimental elements to the alloy can lead to an incredible improvement of the oxidation resistance. New work based on AES, SNMS, TEM and AFM now helps in understanding this effect. Another surprising effect is the formation of silica whiskers on Ni-Si alloys which is now understood and can be modelled.

• Franz Dettenwanger, KWI-DECHEMA
  The Microalloying Effect in the Oxidation of TiAl Materials
• David Young, University of New South Wales
  Rapid Oxidation of Ni-Si Alloys: External Silica Whisker Growth and Internal Precipitate Dissolution

It has been known for a long time that the presence of water vapor in high temperature atmospheres as encounterd in many technical environments may degrade high temperature oxidation resistance. However, there has still been a lack in the understanding of the mechanisms and in its quantification in particular with respect to the type of oxide formed as a protective layer on top of the metallic materials. The two contributions address most recent work in this field which has led to a significant improvement of the understanding.

• Joe Quadakkers, FZ Jülich
  Effect of Water Vapor on the Oxidation Behavior of Alloys Forming Chromium-Rich Surface Scales
• Gerald Meier and Fred Pettit, University of Pittsburgh
  The Effect of Water Vapor on the Oxidation Bahavior of Alumina-Forming Alloys and Coatings

Oxidation is usually regarded as a detrimental process consuming the original metal and degrading the function of metallic components. There are however applications where oxidation is used deliberately to produce certain properties of components. A classic example is semiconductor industries where silica is produced by thermal oxidation of silicon substrates with the aim to get an insulating layer. More recent developments are based on III - V semiconductors where the insulation layer should be pure alumina. Producing such layers is not a trivial issue and research is still giong on. Another area which is still under development is the production of ceramic composites by the oxidation of metal-bearing precursors. This technique is partially known from the production of high temperature superconductors but has been extended also to structural components. In both talks the mechanisms, kinetics and requirements will be addressed.

• Michael Graham and Rex Hussey, NRC
  Oxide Formation on III-V Semiconductors for Device Applications
• Ken Sandhage, Ohio State University
  Near Net-Shaped, Multicomponent Ceramics and Ceramic Composites by the Oxidation of Metal-bearing Precursors

This session starts with a restrospective of an experienced high temperature corrosionist giving a flavor of what the 20th century meant for high temperature corrosion research. The second part of the session consists of a panel discussion of long-term leaders in high temperature corrosion research with the aim to give a perspective on what has to be done at the beginning of the 21st century. The particular purpose of this discussion is to pass on experience and to draw the attention of young researchers to the most important research topics for the future.

• John Stringer, EPRI
  What Pilling and Bedworth Really said, and what Pfeil Actually Patented

Panel Discussion: Demands for Future Work

• Hans Grabke, Max-Planck-Institut für Eisenforschung
• Fred Pettit, University of Pittsburgh
• John Stringer, EPRI