Prøveforelesning
Se prøveforelesningBedømmelseskomité
Professor Lars-Gunnar Johansson, Institutt for Kemi- och bioteknik, Chalmers tekniska högskola, Göteborg, Sverige
Førsteamanuensis Tor Hemmingsen, Institutt for matematikk og naturvitskap, Universitetet i Stavanger
Professor Karl Petter Lillerud, Kjemisk institutt, Universitetet i Oslo
Leder av disputas: Tyge Greibrokk
Veileder: Truls Norby
Sammendrag
It is well known that water vapor affect the corrosion resistance of many chromium-containing alloys by affecting chromium oxide growth rate, and formation of protective chromium oxide scale. Several mechanisms have been proposed in literature in the past. Unfortunately none is comprehensive enough to explain all the effects observed during the corrosion process. However, knowledge of these mechanisms is important for understanding of the corrosion of materials in steam. Presence of water vapor is found in process gases and energy production environments, e.g. in steam power plants, and flue/combustion gases. The development of Fuel Cells (e.g. SOFC) to produce “clean” energy using hydrogen has awakened the interest in water vapor effect on corrosion of materials.
It was found in this study that water vapor affects the transport processes in the material resulting in an enhanced internal formation of chromium oxides thus preventing the development of external protective scale. This could be prevented by increasing the amount of chromium in the material. It was also revealed that the enhanced scale growth rate can be alleviated by adding small amounts (~0.4%) of manganese to the alloy. It was also observed that scale formed in water vapor has very good adherence to the substrate material. The improved scale adherence has the consequence that costly methods to prevent scale spallation are avoided.
To achieve the results above, different materials (FeCr and NiCr model alloys, NiCr-based Oxide Dispersion Strengthened (ODS) alloy and some selected steels for Solid Oxide Fuel Cell (SOFC) application), were tested in respect to corrosion properties exposed at high temperatures (800°C to 1050°C) to gases with and without water vapor. Thermogravimetry which enables continuous observation of the corrosion process was the main test method used. To characterize the corrosion products, corroded samples were investigated using X-ray diffractometry (XRD), light and electron microscopy, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and sputtered neutrals mass spectrometry (SNMS) analyses.
Kontaktperson
For mer informasjon, kontakt Raul Boris Briceno.