| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeP |
| Session: | Energy Harvesting & Storage Poster Session |
| Presenter: | Helen Brannon, Kratos Analytical Ltd., UK |
| Authors: | D. Surman, Kratos Analytical Inc. H. Brannon, Kratos Analytical Ltd., UK J. Counsell, Kratos Analytical Ltd., UK S. Hutton, Kratos Analytical Ltd., UK J. Morrison, University of Birmingham, UK C. Blomfield, Kratos Analytical Ltd. A. Roberts, Kratos Analytical Ltd., UK |
| Correspondent: | Click to Email |
Stainless steels are vital construction materials in all areas of industry, combining excellent corrosion resistance with good mechanical properties. For these reasons, stainless steels are used extensively in power stations of all varieties – of particular interest is the use of stainless steel in Pressurised Water Reactor (PWR) type nuclear power plants, such as the Sizewell B power station, Suffolk, UK.
The corrosion of steel in contact with hot, pressurised water in a PWR is a common problem. This side reaction is undesirable due to the reduced heat transfer efficiency caused by the deposited oxide layers.Stainless steel’s corrosion resistance is derived from the formation of a passivation layer at the surface of the material. Under atmospheric conditions this is thought to be a vanishingly thin layer of Chromia (Cr2O3), however, under conditions found in the coolant cycles of a PWR, it is thought that the passivation layer grown forms a double layer – the inner layer consisting of corrosion resistant, non-stoichiometric Chromite (FeCr2O4), while the outer layer consists of non-stoichiometric Nickel Ferrite (NiFe2O4). The thickness of this film is believed to vary with the steel surface finish, and the Environment Degradation Group at the University of Birmingham has recently begun a programme to study the dependence of corrosion rate and passivation layer thickness on surface finish, system chemistry and temperature.
The samples were ground to a 120 and 1200 grit finish using silicon carbide paper to produce samples with significantly difference roughness levels (approximate Ra values of 1050 and 110 nm, respectively), before being inserted into a flowing rig, where they were exposed to deoxygenated water at pH 10 and 300˚C at a pressure of 10 MPa. Sets of samples were removed from the rig every 250 hours, up to 1000 hours total exposure time.
X-ray photoelectron spectroscopy (XPS) was used to determine the type of corrosion chemistry that occurs. It was combined with a high energy, medium sized argon gas cluster source, which is shown to be advantageous compared to a conventional monatomic argon when depth profiling such layered structures, causing reduced structural and chemical damage from the ion beam sputtering process. Data acquisition at small analysis areas gives well resolved spectra, revealing the multi-layered oxide structures produced from the corrosion process. [1] Depth profiling of the Passive Layer on Stainless Steel using Photoelectron Spectroscopy, Wendy Fredrikkson, Uppsala University [2] Applied Surface Science, 257, (2011), 2717–2730 [3] The Radiochemistry of Nuclear Power Plants with Light Water Reactors, By Kark-Heinz Neeb