The use of XPS and AFS technique has been explored in the stLrly of the surface chemistry of a whole electrode surface (XPS) and the surface chemistry of natural pits (AFS). EDXA and to a snall extend SIMS were also used in the investigation of the individual pits. A high resolution Auger electron microscope which has an analytical resolution as snall as 0.1 .un enables a nevly formed pit of less than 2 .un in diameter to be investigated. By using a Cl/Mg ratio an attempt had been made to correlate the surface chemistry of whole electrodes exposed at different potentials in 1M MgCl2 solution to the surface chemistry of individual pits naturally produced qy means of a simulated metal to metal crevice made of cammercial stainless steels (SS316 and SS304) immersed in 1M MgCl2 solution. '!he correlation was fomd to be good and within the expected limit of the data produced by XPS and AFS. The estimated val ue of potentials of the surface of pit and its immediate vicinity was based on a theoretical model of variation of potential aromd a pit by Melville and also on the potential-current curve of the steel sample in the test sol ution. The Q/Mg ratio was shown to be useful in determining the activity of pits. In repassivated pits in the crevice mouth zone magnesiun was a dominant species relative to chlorine, this is in contrast to the pits in the central part of the crevice which were (ii) engulfed in general corrosion. Active pits in the area between the two regions have higher value of Cl./Mg ratio in their surface than that in the surface in their immediate vicinity. The role of chraniun in pitting corrosion is suggested to counter the pitting attack by the fonnation of chramiun oxide and oxy-chloride on the surface of pit. Molybdenun when present, also concentrates on the surface of pit. The type of corrosion attacks on sulphide inclusions in stainless steel depend on the copper content of the inclusions. Pitting will be likely to take place on pure MnS incl usions but not on copper enriched-MnS inclusions. The fonnation of copper sulphide is suggested to be important in reducing the amount of active species of sulphur on the corroded inclusions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:353300 |
| Date | January 1985 |
| Creators | Daud, A. R. |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/770155/ |
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